Water usage and efficiencies for irrigation in Northern Peru. A ......de Minera Yanacocha S.R.L., la...

Water usage and efficiencies for irrigation in NorthernPeru. A case study in Cajamarca, a region affected by

mining industry. Watergebruik en efficiënties voor irrigatie in Noord-Peru. Een casestudy in Cajamarca, een regio

beïnvloed door mijnbouw.

juni 2015

Promotor:

Prof. Guido Wyseure

Departement Aard- en Omgevingswetenschappen

Afdeling Bodem- en Waterbeheer

Masterproef voorgedragen

tot het behalen van het diploma van

Master of science in de bio-ingenieurswetenschappen:

land- en bosbeheer

Froukje Kuijk

"Dit proefschrift is een examendocument dat na de verdediging niet meer werd gecorrigeerd

voor eventueel vastgestelde fouten. In publicaties mag naar dit proefwerk verwezen worden

mits schriftelijke toelating van de promotor, vermeld op de titelpagina."

Water Usage and Efficiencies for Irrigationin Northern Peru. A Case Study in Cajamarca, a Region affected by Mining Industry

i

Acknowledgements

Making this thesis was like stumbling nine times and getting up ten, both during the fieldwork

in Peru and the processing in Belgium. For me it was more than a thesis: it was five years of

inhaling all possible knowledge to become a good bioscience engineer. This long process could

not be successfully accomplished without the support of all the professors, assistants and fellow

students. I really want to thank all of them for that!

Help in the realization of my thesis, first of all I want to thank my promotor, Guido Wyseure,

for giving me the opportunity to cooperate in the VLIR-project, and for guiding me through the

travel of making a decent thesis. In Peru it took some time before a real take-off, but especially

in that situation the support of the people that helped me finding the right track was incredibly

important. Therefore a sincere gratitude for

- the Grufides crew (Pablo, Hanne, Ophelia, Laura and Coco)

- the professors of the UNC (Nilton, Francisco, Marco, Consuelo and Gilberto)

- the always smiling people of the Junta de Usuarios de Río Mashcón (Luis, Norberto,

Noe, Juan and Cesar)

- the helpful hands of RENAMA, in particular Milagros and Carlos for joining the

multiple fieldworks

- the CASCUS-team, in particular Sonja for the exchange of information and experiences

- Diana, what appeared to be a pity we only met in the end of my stay, because a

cooperation would have been nice

- and all the people that made the stay in Cajamarca feeling as a real hometown, ‘un

hogar’ (Carmen, Rebecca, Nilton, Sophie, Coco, Tany, Carlos, Augusto, Sonja and

Sarah)

I also want to thank CATAPA for all those interesting years that have enrolled me in mining

issues around the globe, and that stimulated me to create a critical awareness. Hanne Van

Gaelen certainly has to be mentioned for her help in the interpretation of Aquacrop. Above all

a special thanks goes to my parents for raising me to the person who I am, believing in me and

being always present! Last but not least: Gracias Camilo, por ser mi Camilo!

For me, this is not a closed chapter, but the beginning of a life where I can start to put all my

education into practice and to make my contribution for a better world.


ii

Summary

In Northern Peru water scarcity in the dry season is a real challenge, especially for agriculture.

This issue augmented in the early 1990s by the introduction of Minera Yanacocha S.R.L, the

second largest gold mine in the world. Both land use types address the same limiting water

sources, inevitably leading to conflicts. Agriculture in this region mainly consists of pasture for

livestock and dairy production, since it is robust to water scarcity. Water, distributed within

irrigation commissions, is supplied by springs, in the higher Sierra, or via offtakes from rivers,

closer to the valleys. Mainly border irrigation is performed, and within one irrigation network,

water is conducted through open channels. In literature, evaluations of irrigation infrastructure,

efficiency and distribution methods in the Northern Andes of Peru are scarce. The usage of

control structures to evaluate exact water quantities entering the channels, is barely

implemented in this region.

The Yanacocha mine is positioned on the source area of several important rivers. Water

pollution, disturbance of the hydrological distribution and reduction of the phreatic level are

the main possible impacts of a mine on the fresh water environment.

In this dissertation the focus is laid on the río Grande de Mashcón and its contributors. A

discharge inventory in this catchment is carried out, based on historical and present measuring

events, and trends of change in hydrology in time are derived. In the irrigation commission of

Tres Molinos three aspects are evaluated. Firstly the conveyance efficiency of the channel

network is determined. The biomass production and irrigation productivity are simulated for

different water supply scenarios. Finally the recently installed control structure is calibrated,

making it ready to use.

It is observed that in the overall hydrology on catchment level a strong flow reduction occurred

in the first years of the exploitation phase of the mine. Since the implementation of MYSRL’s

more conscious water management, discharges in the rivers are stabilized, but the water

withdraw from the open pits did continue. There is evidence for a significant groundwater

reduction, affecting many, non-inventoried, springs in the higher Sierra.

The actual water quantity entering the channels of Tres Molinos does not reach the water license

of 100lps in the dry season. The field water balance simulation demonstrated a biomass


iii

reduction of 15-17%. The performance within the irrigation network strongly depends upon the

soil type and the conveyance efficiency. A water loss along the channel of 5.7lps.km-1 is

observed to exist. Leakage through gates, robbery and removal of water for other purposes are

identified as the main causes. In certain laterals improvement in channel infrastructure,

distribution scheduling and evaluation of the suitability of distribution frequency relative to the

soil characteristics is strongly recommended.

In Peru, decentralization of the power concerning water resources management is still in

process. More support is still necessary for water allocation, infrastructure and efficiencies in

irrigation commissions and in general in defending agricultural values in the highlands of Peru.

The program of PSI Sierra is already a good incentive.

Resumen

En el norte de Perú la escasez del agua en la temporada seca es realmente un desafío, especifico

en agricultura. Esta cuestión se aumentó en el comienzo de los años 1990, por la introducción

de Minera Yanacocha S.R.L., la segunda mina de oro mas grande del mundo. Ambos usos del

suelo se dirigen a los limitados recursos de agua, llevando inevitablemente a conflictos. La

agricultura en esta región consiste principalmente en pastizales para ganadería y producción de

lácteos, puesto que es más resistente al déficit de agua. Repartido dentro de una comisión de

regantes, el agua esta suministrado por manantiales, en la Sierra alta, o por captaciónes en el

río, más cerca de los valles. Principalmente, se utiliza riego por gravedad, donde el agua fluye

dentro de un sistema de riego por medio de canales abiertos. En la literatura, la evaluación de

infraestructura de riego, eficiencias y métodos de distribución en los Andes, al norte de Perú

esta limitado. Estructuras de control, para evaluar caudales exactos llegando a los canales, son

poco utilizados en esta región.

La mina Yanacocha esta posicionada en las cabeceras de algunos ríos importantes.

Contaminación del agua, perturbación de la distribución hidrológica y reducción del nivel

freático son los impactos potenciales principales de una mina en el la hidrologia.

Esta disertación pone el enfoque en el río Grande de Mashcón y sus quebradas. Un inventario

de descargas en esta cuenca ha sido elaborado, basado en mediciónes históricas y recientes, y

tendencias de cambio en la hidrología son derivados. En la comision de regantes de Tres


iv

Molinos tres puntos han sido evaluados. Primero la eficiencia de conducción en el canal ha sido

determinado. La producción de biomasa y la productividad de riego por diferentes escenarios

de suministro de agua han sido simuladas. Finalmente, se ha calibrado la estructura de control,

que habia sido recien instalada.

Se ha observado una fuerte reducción en la hidrología de la cuenca de río Grande de Mashcón

durante los primeros años de la explotación de la mina. Desde la implementación de la gestión

de agua mas consciente de MYSRL, los caudales en los ríos se han estabilizado, pero el bombeo

de agua afuera de los tajos abiertos ha continuado. Hay evidencia de una reducción significante

de los aquiferos, afectando a muchas fuentes de agua, no inventariadas, en la Sierra alta.

La cantidad de agua actual que llega a los canales de Tres Molinos no alcanza la licencia de

agua en la temporada seca. La simulación ha demostrado una reducción de biomasa de 15-17%.

El desempeño dentro de la red de riego depende mucho del tipo de suelo y de la eficiencia de

conducción. Se ha observado una perdida del agua a lo largo del canal siendo 5.7lps.kmˉ¹. Han

sido identificadas las causas principales como fugas por compuertas, robo de agua o prestamos

con otros fines. En algunos laterales un mejoramiento de la infraestructura, del horario de turnos

y evaluación de la adecuación de la frecuencia de la distribución con respeto de las

caracteristicas del suelo esta altamente recomendado.

En el Perú, la descentralización del poder respecto al manejo de los recursos hídricos esta

todavía en proceso. Más apoyo aún es necesario para la asignación del agua, infraestructura y

eficiencias en comisiónes de regantes y en general para defender los valores agrarios en la Sierra

de Perú. El programa de PSI Sierra ya es un buen incentivo.

Samenvatting

In het droge seizoen in Noord-Peru is water schaarste een echte uitdaging, vooral voor

landbouw. Deze kwestie is verergerd in begin 1990 door de introductie van Minera Yanacocha

S.R.L. in de regio, de tweede grootste goudmijn ter wereld. Beide landgebruiken vereisen

dezelfde limiterende waterbronnen, wat onvermijdelijk leidt tot conflicten. Landbouw in de

noordelijke Andes bestaat hoofdzakelijk uit graslanden voor veeteelt en zuivelproductie,

voornamelijk omdat dit een robuust landgebruik tegen water deficit is. Water voor

irrigatiedoeleinden wordt in de kanalen aangevoerd vanuit brongebieden, in de hogere Sierra,

of via captaties op rivieren, dichterbij de valleien. Waterallocatie gebeurt binnen één irrigatie


v

commissie of comité. Op perceel niveau wordt hoofdzakelijk oppervlakkige irrigatie toegepast,

gebruikmakend van natuurlijke gravitatie, en distributie gebeurt via open kanalen. Een

degelijke evaluatie van de irrigatie infrastructuur, efficiëntie en distributie methodes in de

noordelijke Andes in Peru, schiet tekort in de literatuur. Controle structuren in

irrigatiesystemen, als eenvoudige meetinstrumenten voor instromende debieten, worden

nauwelijks gebruikt in de regio.

De Yanacocha-mijn is gelegen in het brongebied van verschillende rivieren. Water

contaminatie, verstoring van de hydrologische distributie en daling van het freatisch niveau zijn

de belangrijkste potentiële impacten van mijnbouw op de hydrologie.

Deze thesis focust op het Grande de Mashcón stroomgebied. Een debiet-inventarisatie in dit

bekken is uitgewerkt, gebaseerd op historische en recentere metingen, en trends in verandering

van de hydrologie in de tijd zijn afgeleid. In the irrigatie commissie van Tres Molinos zijn drie

aspecten geëvalueerd. Ten eerste is de conductie efficiëntie in the irrigatienetwerk bepaald. De

biomassaproductie en de irrigatie productiviteit zijn gesimuleerd voor verschillende

wateraanvoer scenarios. Als laatste is de recent geïnstalleerde controle structuur gekalibreerd

zodat deze klaar is voor gebruik.

Er is geconstateerd dat de hydrologie binnen het Grande de Mashcón bekken met sterk

verminderde debieten kampte in de eerste jaren van de exploitatiefase van de mijn. Vanaf de

implementatie van MYSRL’s meer bewust water management, zijn de debieten in naburige

rivieren terug gestabiliseerd, maar het oppompen van grondwater uit de open pits zette zich

voort. Er zijn duidelijke aanwijzingen voor een significante reductie van de grondwatertafel,

met vele geaffecteerde, niet-geïnventariseerde, waterbronnen in de hoger gelegen gebieden, tot

gevolg.

The actuele water volumes, die binnenstromen in de kanalen van Tres Molinos, bereiken in het

droge seizoen de licentie-waardes niet. De simulatie heeft aangetoond dat er een biomassa

reductie van 15-17% optreedt indien er met een actueel debiet geïrrigeerd wordt, in vergelijking

met het licentie debiet. De efficiëntie van de waterinput waarmee biomassa wordt opgebouwd

hangt sterk af van het type bodem en de geleidingsefficiëntie. Een waterverlies in de kanalen

van 5.7lps.kmˉ¹ is waargenomen. Lekkage door poorten, diefstal en tijdelijk gebruik van water

voor andere doeleinden zijn geobserveerd als de belangrijkste oorzaken. In sommige lateralen

wordt een verbetering van de irrigatie-infrastructuur, distributieplanning en evaluatie van de


vi

geschiktheid van de distributiefrequentie ten opzichte van de bodemkarakteristieken, sterk

aanbevolen.

Decentralisatie van het Peruviaans beleid inzake water management is nog lopende. Betere

ondersteuning van waterallocatie, infrastructuur en efficiëntie in irrigatie commissies wordt

sterk aanbevolen en meer algemeen is het verdedigen van agrarische belangen in de Sierra van

Peru essentieel. Het programma PSI Sierra is reeds een goede aanzet.


vii

List of abbreviations

ALA-C Autoridad Local del Agua de Cajamarca

ANA Autoridad Nacional del Agua

ATDR Administración Técnica de Distrito de Riego

AW Augusto Weberbauer agrometeorological station

BT Bocatoma

COMOCA Comisión de Monitoreo de Caneles de Riego Cajamarca

CSR Corporate Social Responsibility

CTF Cutthroat flume

DM Dry Matter

ET0 Reference Evapotranspiration

EA Environmental Audit

EIA Environmental Impact Assessment

EPS Sedacaj S.A. Empresa Prestadora de Servicios de Saneamiento S.A. Cajamarca

GDP Gross Domestic Product

IMT Irrigation Management Transfer

INRENA Instituto Nacional de Recursos Naturales

ITCZ Inter Tropical Convergence Zone

JURM Junta de Usuarios del Río Mashcón

MINAG Ministerio de Agricultura

MINAGRI Ministerio de Agricultura y Riego

MYSRL Minera Yanacocha S.R.L.

O&M Operation and Maintenance

RAW Readily Available Water

RENAMA Gerencia Regional de Recursos Naturales y Gestión del Medio

Ambiente (Regional Government)


viii

REW Readily Evaporable Water

Senamhi Servicio Nacional de Meteorología e Hidrología del Perú

Sierra Highlands

SSJC Irrigation Committee Salvador San José de Coremayo

TAW Total Available Water

TM Irrigation Commission Tres Molinos

UNC Universidad Nacional de Cajamarca

WFD Water Framework Directive

WPb Biomass Water Productivity

WPirr Biomass Irrigation Water Productivity

WRB World Reference Base for Soil Resources

WUA Water User Association

ZEE Zonificación Ecológica y Económica (Regional Government)


ix

List of Figures

Figure 1 Location of the Mashcón (WGS 84/ UTM zone 17S) and the Crisnejas (SIGMINAM,

2010) catchment ......................................................................................................................... 5

Figure 2 Typical gate for division purposes; distribution between channels or field inlet ...... 10

Figure 3 Design parameters of a cutthroat flume (Skogerboe et al., 1973) ............................. 13

Figure 4 General lay-out of border irrigation (Wyseure, 2014). .............................................. 16

Figure 5 Demarcation of the AAA’s in Peru according to hydrological units (Pinto Ortiz, 2008)

.................................................................................................................................................. 20

Figure 6 Mining district of MYSRL with indication of different open pits, discharge outlets,

neighbouring irrigation infrastructure, hydrology and the catchment divide. .......................... 22

Figure 7 Nomenclature of the hydrology of the río Grande. .................................................... 28

Figure 8 Schematic representation of the irrigation network in the commission Tres Molinos.

Distances (measured in Q-GIS), starting from the bocatoma are indicated in km. .................. 29

Figure 9 Rectangular cutthroat flume in Tres Molinos within the project of PSI Sierra ......... 30

Figure 10 Soilscape classification of Tres Molinos ................................................................. 31

Figure 11 Elevation profile from the Rosario Horco hill to the Shilla knolls .......................... 33

Figure 12 Monthly and annual representation and boxplots of the 1973-2014 precipitation time

series of the AW station (UNC and Senamhi, Cajamarca) ...................................................... 37

Figure 13 Deviation in dimensions in the installed rectangular cutthroat flume in Tres Molinos

.................................................................................................................................................. 41

Figure 14a General growth cycle for crops in Aquacrop (FAO, 2013) b Typical growth cycle

for forage crop (Allen et al., 1998) ........................................................................................... 47

Figure 15 Measured discharges (in lps) of the brooks of the río Grande in June and July 2007

.................................................................................................................................................. 49

Figure 16 JURM and representatives of their irrigation commissions visiting dam río Grande in

October 2014 ............................................................................................................................ 50

Figure 17 structure of the Shilla secondary channel. ............................................................... 60


x

List of Tables

Table 1 Indicative conveyance efficiency in irrigation channels (Brouwer et al., 1989). ........ 15

Table 2 Boundaries within basin and irrigated water systems (Lankford, 2012). ................... 18

Table 3 Net water consumption in the Merill-Crowe process, the activated carbon columns and

the casting of MYSRL in 2006 (Yacoub López and Cortina Pallás, 2007) ............................. 23

Table 4 Main characteristics of the 12 outlets of MYSRL mining zone and their receptor water

bodies (Grufides, 2012) ............................................................................................................ 24

Table 5 Meteorological stations of Senamhi nearby the city Cajamarca. ................................ 35

Table 6 Monthly mean and standard deviation of precipitation (mm) 1973-2014 of the station

AW (UNC and Senamhi, Cajamarca) ...................................................................................... 37

Table 7 General statistics and trend analysis of meteorological variables of the AW station . 39

Table 8 Different water supply scenarios for the evaluation of the irrigation performance in the

field water balance of Tres Molinos ......................................................................................... 44

Table 9 Irrigation application (in mm) for the 4 soil types in the license and actual scenario, as

management input data in Aquacrop ........................................................................................ 45

Table 10 Curve Numbers and Readily Evaporable Water for the four soil type ..................... 45

Table 11 Soil characteristics for soil type Phaeozem ............................................................... 45

Table 12 Soil characteristics for soil type Leptosol ................................................................. 46

Table 13 Soil characteristics for soil type Vertisol ................................................................. 46

Table 14 Soil characteristics for soil type Andosol .................................................................. 46

Table 15 Available historical discharge (m³.s¹־) data of monitoring point on the río Grande . 48

Table 16 Results parametric and non-parametric trend analysis on discharge measurements

(elaborated by COMOCA) in irrigation channel in the direct vicinity of MYSRL. ................ 50

Table 17 Measured upstream heads (m) and discharges (m³.s¹־) for free flow calibration of the

CTF in Tres Molinos ................................................................................................................ 52

Table 18 Characteristics of the trend lines, based on the measured height-discharge relations,

and recalculated discharges according to an excel power, the design, Manekar et al and

Temeepattanapongsa et al equations. ....................................................................................... 52

Table 19 Measured discharges (in lps) along the main channel and secondary channel of Tres

Molinos, in function of the distance of the bocatoma. ............................................................. 54

Table 20 Mean conveyance efficiency (%) per soil type in TM .............................................. 55

Table 21 Total irrigation depth (in mm) for the 4 soil types and 3 irrigation scenarios .......... 55

Table 22 Profile and TAW characteristics of the 4 different soil types ................................... 56


xi

List of Graphs

Graph 1 Time series of the cumulative annual precipitation (mm) 1934-2014 of the station AW

(UNC and Senamhi, Cajamarca). ............................................................................................. 36

Graph 2 Scatterplot of the precipitation dataset of 1973-2014 (UNC and Senamhi, Cajamarca).

Regression is indicated through the car-package (Fox and Weisberg, 2015) .......................... 38

Graph 3 Graphical representation of the different trend lines. ................................................. 53

Graph 4 Loss in discharge (lps) as a function of the distance (m) from the bocatoma running

over the main, secondary and tertiary channel of Tres Molinos .............................................. 54

Graph 5 Resulting biomass (ton DM ha¹־) of pasture growth in the dry season for 4 soil types

and 3 irrigation situations in Tres Molinos .............................................................................. 56

Graph 6 Biomass Water Productivity (kg.m־ᶟ) of pasture growth in the dry season for 4 soil

types and 3 irrigation situations in Tres Molinos ..................................................................... 56

Graph 7 Biomass Irrigation water Productivity (kg.m־ᶟ) of pasture growth in the dry season for

4 soil types and 3 irrigation situations in Tres Molinos ........................................................... 57


xii

Contents

1 Introduction ......................................................................................................................... 1

1.1 Irrigation systems and their efficiencies in the northern Andes of Peru ..................... 1

1.2 Mining practices and impacts on natural hydrology and water quantities .................. 2

1.3 Problem definition ....................................................................................................... 3

1.4 Objective ...................................................................................................................... 4

2 Literature review ................................................................................................................. 5

2.1 Catchment Mashcón .................................................................................................... 5

2.1.1 Climate ................................................................................................................. 6

2.1.2 Ecology ................................................................................................................. 6

2.1.3 Geology and pedology ......................................................................................... 7

2.2 Agricultural Practices in the northern Andes of Peru .................................................. 8

2.2.1 Type of agriculture ............................................................................................... 8

2.2.2 Irrigation and water distribution methods ............................................................ 8

2.2.3 Efficiency in irrigation networks ........................................................................ 15

2.2.4 Supporting framework and institutions .............................................................. 18

2.3 Mining practices of MYSRL and impacts on natural hydrology .............................. 21

2.3.1 Dam río Grande .................................................................................................. 26

3 Materials and methodology ............................................................................................... 27

3.1 Study Area ................................................................................................................. 27

3.1.1 The Grande de Mashcón catchment ................................................................... 27

3.1.2 Tres Molinos ...................................................................................................... 28

3.2 Agrometeorological data ........................................................................................... 34

3.2.1 Precipitation analysis .......................................................................................... 36

3.2.2 Analysis of other meteorological variables ........................................................ 38

3.3 Discharge inventory Grande de Mashcón catchment ................................................ 40

3.4 Infrastructure evaluation: Flume Calibration ............................................................ 40

3.5 Efficiencies of the irrigation network ........................................................................ 42

3.6 Field water balance .................................................................................................... 42

3.6.1 Survey ................................................................................................................. 43

3.6.2 Environment and crop ........................................................................................ 43

3.6.3 Simulation strategy for forage crops .................................................................. 46

4 Results ............................................................................................................................... 48


xiii

4.1 Discharge inventory Grande de Mashcón catchment ................................................ 48

4.2 Calibration of the CTF ............................................................................................... 51

4.3 Efficiency of the irrigation network .......................................................................... 53


5 Discussion ......................................................................................................................... 58

5.1 Water availability in the Grande de Mashcón catchment .......................................... 58

5.2 Calibration of the CTF ............................................................................................... 59

5.3 Efficiency of the irrigation network .......................................................................... 59


6 Conclusion ........................................................................................................................ 64

7 References ......................................................................................................................... 66

8 Annexes ............................................................................................................................. 72


1

1 Introduction

Worldwide agriculture takes by far the largest share, of about 80%, of the total water withdraw

(Shiklomanov, 1999; via Vos, 2002; Garces-Restrepo et al., 2007). Regardless of this fact,

water is still the limiting factor for food production and agricultural practices, especially in

those regions that have a low annual rainfall or a strong contrast between the dry and wet season.

The outset of different land use types that seek for the same limiting water sources together

with growing population pressure are driving forces to improve efficiency and modelling the

exact water requirements in agriculture. The province of Cajamarca, in the northern highlands

of Peru, is struggling nowadays with the same issue. Agriculture, the dominating land use for

the past centuries, has been facing strong competition for water resources from Minera

Yanacocha S.R.L. (MYSRL) since the nineties. This goldmine is located on the sources of the

rivers that drain towards the valleys and that mainly supply water for irrigation purposes along

their way. In this research an evaluation of water usages between different land use types is

carried out and an example is given of a validation and characterisation of the required water

supply in an irrigation commission and the efficiency of the irrigation network. This is an

exploratory research in the framework of the long-term interuniversity project ‘Impact on

surface water resources and aquatic biodiversity by opencast mining activities in Cajamarca,

Peru’ between the Katholieke Universiteit Leuven (KU Leuven) and Universidad Nacional de

Cajamarca (UNC).

1.1 Irrigation systems and their efficiencies in the northern Andes of Peru

Since pastures and dairy cattle are the most robust agricultural activities to water scarcity in the

dry season, farmers in the highlands have been living for centuries from milk production.

Especially the last decades it is a key component in the economy of Cajamarca, leading to a

dairy production increase of more than 4% per year (Garcia and Gomez, 2006). This land use

is developed towards a balance with the available water sources, although it already approaches

the limits of natural land covers (Tovar et al., 2013). The irrigation practices in the dry season

are strongly imbedded in social structures, ensuring a good irrigation water distribution and

maintenance of infrastructure. With a certain amount of irrigation hours for each farmer, the

water is supplied via channels and applied on the fields through border strip irrigation. Decent

evaluation, possible improvement of or governmental support for these irrigation systems has

been disregarded for decades, since most of the inversion had gone to the large-scale coastal


2

cultivations. The current water policy in Peru, that pushes farmers to more efficient water usage

(Boelens and Vos, 2012), and a radical change in natural water distribution as a result of the

instantaneous establishment of the Yanacocha mine, requires a proper evaluation of available

water sources, an inventory of water users and their water rights, a localisation of water losses,

and possibilities for improvement.

However an important footnote has to be made regarding efficiencies and losses in irrigation

systems. The current agricultural system that has grown gradually over decades has to be

considered as holistic in its water usage. Farmers that make use of irrigation water are

unavoidably connected with other water users up and downstream. Water can be lost in a certain

irrigation network out of its own perspective, but could be advantageously recovered in another

location of the drainage basin (Lankford, 2012).

1.2 Mining practices and impacts on natural hydrology and water

quantities

“Yanacocha is Newmont's prize possession, the most productive gold mine in the world. But if

history holds one lesson, it is that where there is gold, there is conflict, and the more gold, the

more conflict” stated Perlez and Bergman, (2005) in The New York Times. MYSRL, operating

already for more than 20 years in the Cajamarca province, is worth over $7 billion. The annual

production of the mining sector in Peru accounts for 4.1% of the GDP. Noteworthy is the recent

report elaborated by Wiener and Torres, (2014), revealing that MYSRL had dodged the

Peruvian taxes over the years by overestimating costs, illegal mercury sale, land grabbing and

generating unprecedented depreciations amongst others, and so evading billions of dollars. On

local scale, Aragón and Rud, (2013) observed a positive impact of this mine on the economy,

since the late 1990’s, driven by the explicit corporate policy of the International Finance

Corporation. Also the so called ‘Canon Minero’1, will have contributed to the local authorities

of the Cajamarca province. On the other hand more recent research questions the economic

benefits of mining industry for the local population. Ticci and Escobal, (2015) point out that a

greater corporate social responsibility of mining companies in Peru did significantly increase

employment for migrants from other regions, but failed in local support. Peru is one of the

fastest growing economies in Latin America, but the poverty gap remains large, especially in

1 Of the taxes called in from a company, 50% will go to the local government


3

Cajamarca (the World Bank, 2013). Introduction of mining in areas in Peru also has a negative

impact on the labour share of agriculture (Ticci and Escobal, 2015), which is mostly the case

when no quid pro quo is actively initiated, e.g. financing irrigation infrastructures, capacity

building, etc. Generally both land use types strife for the same sources like water and land.

Younger and Wolkersdorfer, (2004) distinguish 4 general legitimate impacts of mining

operations on the fresh water environment, that can be relevant for nearby agricultural activity:

- Excavating open pits (disruption of superficial and subterranean hydrological pathways)

- Discharging waste water from mineral operations and seepage of leachate from piles

and tailing dams (water contamination downstream)

- Mine dewatering

o Disposal of the pumped water (surface or groundwater pollution)

o Lowering of the water table (decreased flow and volume in water bodies in the

vicinity of the open pit, land subsidence)

- Post-mining flooding and uncontrolled discharge of polluted waters (disturbance and

damage of water quantity, distribution and quality)

The Peruvian Ombudsman reported 129 socio-environmental conflicts in 2009, of which 65%

were mining related (Ticci and Escobal, 2015). Worldwide disputes occur between mining

companies and water users. In this research the focus will be laid on the water quantity and

allocation changes of the Yanacocha mine confronting agriculture and irrigation practices.

1.3 Problem definition

The Yanacocha mine consumes annually large water volumes. The water demand of the

population increases as well due to its related strong growth. Water rights are assigned by

governmental institutions that lack a proper inventory or base line about the available water

sources and their usage.

Because of this problematic competition for water, mainly between the mining industry and

agriculture, water scarcity becomes more than ever a severe problem for Cajamarquino farmers

in the dry season. In addition, the lack of proper measuring devices or control structures makes

it more difficult for farmers to claim the water they are entitled to. The Peruvian government

triggers irrigated agriculture to make more efficient use of their sources, but until recently there

was no governmental support and interest in the Sierra, since the more commercial cultivations


4

are located in the coastal zone. In literature, evaluation of irrigation infrastructure and

distribution methods in the northern Andes of Peru are scarce. In this entire context, a good

characterisation of water availability, usage in different land use types and efficiencies in

irrigation are essential. This research will be carried out in the Mashcón catchment, which is

the most densely populated of all the catchments in the influence zone of the Yanacocha mine

(MYSRL, 2007).

1.4 Objective

The objective of this research is two-fold. At first it will be attempted to achieve an overview

of water usage and distribution over different land use types in the Grande de Mashcón

catchment. To observe a possible change in water availability for agriculture, historical data of

discharges in the río Grande and its contributors will be addressed, and clear changes or trends

will tentatively be explained within the context of Cajamarca. Secondly the focus will be laid

on one specific irrigation commission (Tres Molinos), supplied by the río Grande. A detailed

description and evaluation of its water supply, conduction and distribution will be carried out.

In relation to the water distribution over the entire river a control structure will be calibrated.

This can be useful for improved future comparison of the water volumes entering the main

channel according to the license the commission pays for, with the other commissions or water

consuming activities in the catchment. The efficiency over a part of the channel network will

be measured and evaluated, and recommendations for improvements will be given. Finally a

field water balance will be set up to evaluate the irrigation performance in the dry season in

relation to the license and the actual supply, and in comparison with the performance if no water

stresses would occur. This balance will be simulated with Aquacrop. With these three targets

in this irrigation commission a general image is drafted on how farmers use their water, and

what the exact impact is of water scarcity.


5

2 Literature review

2.1 Catchment Mashcón

Figure 1 Location of the Mashcón (WGS 84/ UTM zone 17S) and the Crisnejas (SIGMINAM, 2010) catchment

The Mashcón catchment, is located in the northern Andes of Peru with coordinates 7°08’ South

and 78°33’ West. It is part of the catchment Crisnejas, situated on the border of the continental

watershed divide of the Americas. In contrast to the rivers of the western adjacent catchments

of Jequetepeque and Chicama that drain to the Pacific ocean, the rivers of the Crisnejas

catchment culminate in the río Cajamarquino which flows into the río Marañon. The latter is

one of the main sources of the río Amazon which ends up in the Atlantic ocean. The Mashcón

catchment is approximately 31,500 ha ranging from 2500-4100m asl; Figure 1. This catchment

can be divided into smaller units that are drained by the río Porcón, río Grande de Mashcón,

río Samber, río Paccha and río Tres Ríos. In this study there will be focussed on usage of water

resources in the catchment of Río Grande de Mashcón, that further will be called the río

Grande, which drains an area of 7,390 ha. The Yanacocha mine is situated on the former main

sources of the río Grande. The water used in the mining operations is partly discharged into

this river, making the hydrology completely artificial. Of the total population of the department

of Cajamarca, numbering around 1.514 million habitants (INEI, 2012; via Ministerio de

Vivienda, 2012), 67% is rural (INEI, 2007). The district of Cajamarca itself comprised in 2008


6

162,326 inhabitants (INEI, 2008; via Steel, 2013). The introduction of MYSRL was the most

prominent driver of an intensive population growth in Cajamarca city. Between 1993 and 2007,

this growth (4%) was even de double of Peru’s capital, Lima (2%) (Steel, 2013).

2.1.1 Climate

Cajamarca has a semi-arid cool climate with dry winters and rainy summers according to the

Köppen climate classification. The movement of the ITCZ gives rise to a division of this dry

and a wet season, respectively from May to September and from October to April. The average

annual precipitation varies between 300-900mm, but depends strongly on the elevation.

Minimum and maximum temperatures do not vary a lot during the year. For a rough

extrapolation of temperatures with height a decrease of 0.67°C.100m¹־ elevation can be used

(Hijmans et al., 1999). Because of the presence of the Humboldt current, the ENSO-activity has

a certain effect on the regional climate, especially on the coastal area but also on inter-Andean

regions like Cajamarca.

2.1.2 Ecology

Natural vegetation in the northern Andes is mostly depending on the changes in climate over

an altitude gradient. According to Pulgar- Vidal (1996; via Krois and Schulte, 2013) Cajamarca

can be classified under Quechua and Jalca ecosystems. The Quechua zone is located 2300-

3500m asl, where natural vegetation hardly still occurs and is mostly altered by agricultural

crops, pasture for grazing and eucalyptus plantations. With increasing altitude night frosts in

the winter, higher wind speeds and larger amounts of precipitation are more common. Jalca is

the natural land cover on elevations 3500-4000m asl. It is an alpine grassland vegetation,

between the upper limit of continuous forests and the snow line, primary present in the northern

Andes of Peru (Luteyn, 1999). The Páramo is a similar ecosystem which is encountered on

higher latitudes. The Jalca is growing on a wider range of soil types. The ecosystems developed

on volcanic ash soils, that are more abundant in de Páramo ecosystem, are characterized by a

higher water retention capacity (Cammeraat et al., 2014).


7

2.1.3 Geology and pedology

In the Mesozoic a sedimentation plinth was formed by marine deposits. Within the Mashcón

catchment from the Cretaceous period the limestone of the Cajamarca formation and the

quartzite rocks of the Farrat formation are the most resistant to weathering and erosion

(Cammeraat et al., 2014). Other formations are featured by deposited rocks like shale, marl and

sandstone.

The orogeny of the Andes, during the Cretaceous and the Paleogene, was caused by the

subduction of the Nazca plate underneath the South American plate. Rapidly heavy volcanic

activity, metamorphism, erosion and sedimentation of rocks took place. For the region of

Cajamarca, and especially the Mashcón catchment, the extrusions of the volcano San Pablo in

the Oligocene, and the Huambos in the Neocene, are the most important. The deposits of San

Pablo exist of agglomerate, breccia, tuff and pyroclastic rock. In some places the well banked

and poorly sorted pyroclastic rock has formed ignimbrite, on which only shallow soils develop.

The volcanic deposits of Huambos are more characterized by plains of acidic tuff (Vásquez and

Crisólogo Rodríguez, 2009). The geologic landscape is often interrupted by resistant

outcropping granite intrusion remnants from the late Tertiary.

In the Quaternary the whole area was covered with glaciers. Interglacial periods induced river

incision, fluvio-glacial and alluvial erosion, transportation and deposition of moraines and basal

till. Lakes have been formed in the valleys, where lacustrine deposition took place. This can be

confirmed by the heavier soils in the depression of the lowlands of the Cajamarca province.

The variety of soils in the Mashcón catchment are mostly determined by their topography and

parent material. Topographical maxima are mostly set by resistant rocks and have a rather poor

soil formation like Leptosols. On the hillslopes Cambisols can be found. On the other hand,

marls and limestone give rise to Phaeozems and Vertisols. More developed ignimbritic and

granitic parent material form rather Umbrisols or Andosols (Cammeraat et al., 2014). These

soils are more sensitive to degradation as result of land use. In the valley bottoms Histosols,

Gleysols and Vertisols are determined by possible high ground water tables and lacustrine

material.


8

2.2 Agricultural Practices in the northern Andes of Peru

2.2.1 Type of agriculture

Only a limited area in the Andean highlands is appropriate for agriculture, because of the steep

slopes with their related erosion risks, outcropping bedrocks and extreme cold and dry

circumstances at high altitudes (Landa et al., 1978). However the northern Andes have a slight

more humid climate in comparison with the southern Sierra in Peru (Urrutia, 1996). Livestock

farming is throughout the Peruvian Andes the most conventional to enhance farmers income

since less risk is associated, considering the unpredictable environment (Mosley, 1982; via Vera

et al., 2006), with as main shortcoming access to irrigation water (Garcia and Gomez, 2006).

The province of Cajamarca is one of the three main dairy producing areas of Peru (Bernet et

al., 2001). The valleys are the most convenient for agriculture, and consequently these farms

are on average larger and more commercial in comparison to the smallholder farms above

altitudes of 3500m asl. The cultivated pasture and forage are mainly alfalfa, oat, and/or

ryegrass-clover, however at higher altitudes natural pasture is mainly used because lack of

irrigation water impedes decent yields of less adapted grass types (Wedderburn and Pengelly,

1991; Bernet et al., 2001). Milk production in Peru increased annually 4.5%, 2% and 9.8%,

respectively between 1996-2002, 2002-2003 and 2003-2009 (Garcia and Gomez, 2006;

MINAG, 2009 ; Espinoza Aliaga et al., 2012). 75% of the milk produced in Cajamarca reaches

the formal chain processing sector, with as main companies Nestlé, Gloria and Laive (Espinoza

Aliaga et al., 2012), the rest is traded to cheese making factories or artisanal sold (Garcia and

Gomez, 2006). Although pastures with livestock farming is a good choice in the higher Sierra

of Cajamarca, alteration with a low intensity of cash crop cultivation, usage of improved grass-

cultivars if irrigation water is available, fodder storage for the dry season and an extra off-farm

salary per household to increase investment can all contribute to a more stable income and

higher dairy production (Bernet et al., 2001; Garcia and Gomez, 2006).

2.2.2 Irrigation and water distribution methods

In the Peruvian highlands the topography and type of water body defines the way farmers

organise themselves for irrigation. The main ‘ojos del agua’, which are literally "water eyes",

a typical term for springs, are located in the higher Sierra. The water of several of these springs

can be captured, conducted through channels, and supply water users. On brooks and rivers that

have a significant enough discharge a ‘bocatoma’ (BT), an offtake regulated by a gate, can


9

initiate a channel that provides irrigation water for a larger area. All the water users that use the

same channel form a Comision de Regantes or a Comité de Regantes, respectively a

commission-, and committee of irrigators. In practice a commission is larger and often more

downstream located, making use of BTs on rivers.

The main channel in commissions and committees can be made in concrete or earth. The

secondary and possible tertiary channels are all earthen channels. On field level, border

irrigation is the most common technique. It is cheap, easy and the natural height differences are

used to have a roughly homogeneous distribution over the parcel. Pressurized irrigation in

mountainous areas can perform well if the system is appropriate for the specific needs of the

farmer (Kastelein, 1998; Bernet et al., 2002). These systems are mostly not used if a large flow

via a BT is delivered. Water is tapped from a spring or a well. The parcel has to be located in

the right position in relation to this source. The discharge from the spring determines the

irrigation frequency. Ramalan and Hill, (2000) tested successfully ‘gravity sprinkle irrigation’

that uses the height difference to drive the required pressure, however the right position of the

parcel and enough elevation difference are restraints. Bernet et al., (2002) concluded that in the

Sierra of Cajamarca it is possible to irrigate the double of an area with sprinklers in comparison

with surface irrigation. Also less erosion problems occur which is an important advantage on

steep slopes. On the other hand higher investment costs and good planning are necessary and

in reality farmers are strongly dependent on technical and financial support of NGO’s (Bernet

et al., 2002), which makes them less self-reliant. Kastelein, (1998) stressed the fact that the

performance of sprinkler systems in the Peruvian highlands strongly depends on the social and

organisational structure, and so it is certainly not always an improvement of conventional

irrigation.


10

Figure 2 Typical gate for division purposes; distribution between channels or field inlet

In the case of surface irrigation water flows, division is managed by gates that are manually

opened and closed (example in Figure 2). The distribution is performed by ‘turnos’, or hour

blocks. A water user gets an amount of hours that his gate will be open, according to the size

of the area he has to irrigate and the related amount of money he pays for. This information is

summarized in the ‘padron de usuarios’. Every commission or committee pays for a certain

water right. In Peru irrigation water is charged per hectare and also worldwide this is the most

common way of pricing (Cornish et al., 2004). However Volumetric Water Control (VWC) is,

by several authors, seen as the best method to improve the irrigation water delivery and keep

the efficiency optimal (Tarimo et al., 1998; Vos, 2002; Cornish et al., 2004). It consists of

charging the exact volume of water that enters the farmers field. However Dono et al., (2010)

criticizes this method, within the objectives of the WFD of Europe. He states that this pricing

strategy can result in overexploitation of groundwater sources, by farmers that have an easy

access hereto, and an overall control and legislation for this issue is often lacking. VWC is also

not realistic for small-holder farmers (Cornish et al., 2004). It is already difficult to have

measuring devices at BT level. Measuring water volumes entering the BT can help already to

raise awareness of how many water there is available at catchment level and to improve the

distribution between offtakes on one river.

In comparison with the committees, the commissions have a stronger participation in the Water

Users Association (WUA), the umbrella organisation of all commissions and committees within

one catchment. Beside the cleaning and maintenance of their own channels, they also formulate,


11

elaborate and control the Operation and Maintenance (O&M) of the common infrastructure

within the WUA, elaborate the regulation of the O&M of the irrigation system and organize

annually, together with the WUA, a teambuilding event, with as main objective to evaluate and

improve the O&M (MINAG, 2005). Within the WUA and the commissions/ committees there

are several roles concerning the distribution of the water and the O&M of the infrastructure:

- Presidente (chairman or president): There is a president of the WUA and several

separate ones per commission and committee. They are elected by the members of

respectively the WUA and the commission/ committee once in the 4 years. In both cases

the president is a water user himself. He is the general representative of respectively the

WUA and commission/ committee.

- Gerente tecnico (technical manager): He is part of the board of the WUA. It is the

engineer that handles the padron de usuarios, hydraulic issues, flow measurements and

the technical aspect of the infrastructure.

- Sectorista: This person verifies whether the water is well distributed over the different

BTs on the river, and evaluates and communicates problems to the gerente tecnico and

the presidentes. In the dry season the water supply is not the sum of the licences of for

example the different commissions on the same river. In these circumstances the

sectorista has to manage that no channel completely falls dry (Briones Arrascua et al.,

2014).

- Repartidor: He has to ensure that every farmer unit/ tertiary block gets his turn in time

according to the roles de riego, a form, of every water user, that indicates how many

hours he gets on what date and time. Mostly all the commissions have a repartidor, but

not all the committees do. In the latter the president would fulfil this task (Vos, 2002).

- Vigilante: This person has to pass several times a day the main and secondary channels

and has to be available to solve disputes or avoid illegal practices like robbing water

(Briones Arrascua et al., 2014).

2.2.2.1 Control structures

Control structures are of great importance, especially in the catchments around Cajamarca

where water shortages and their related conflicts between land use practices are raising, and

discharge measuring equipment is usually not available. Until today measuring discharges by

‘flotador’ or floater is the most common technique. A random object, mostly a branch or a leaf,


12

is thrown in the water and the time over a certain distance of the channel is measured. Hereafter

the velocity and, with the dimension of the channel, the discharge can be calculated. A

correction factor k, varying between 0.66 and 0.80, is used in case the flow is slowed down at

the sides and bottom of the channel, if it concerns an earthen channel or if vegetation is growing

(MINAG, 2004). The use of control structures is in the beginning of its implementation in

irrigation infrastructure in Cajamarca, mainly by the PSI-project (explained in 2.2.4). Real

understanding and usage of the structures is not yet the case. In the same PSI-project a

rectangular cutthroat flume (CTF) was installed at 67m behind the BT of the Tres Molinos

commission, what makes a brief literature review about CTFs relevant.

Flumes are popular discharge measuring structures. Properly calibrated, control structures

display very accurate discharges. They consist of a contraction of the sidewalls, and/or a

possible drop or rise of the channel floor, both to accelerate the flow and initiate a hydraulic

jump. At a certain distance before the constricted section, when the flow is still subcritical, the

water level can be measured and converted in a discharge.

The most commonly used flumes are the Parshall flume and the RBC-flume. In the latter

sedimentation or inhibition of flow can occur, because it consist of a section with a raising

slope. The Parshall flume convergences and divergences with a typical throat-section and a

drop in the channel floor in between. In comparison with the well-known Parshall flume, the

invention of the CTF is recent. Although there is evidence that this concept was already used

in the beginning of the 20th century for irrigation in the Punjab (Vlotman, 1989), the design and

mechanism is for the first time well documented in 1967 by Skogerboe et al. In Figure 3 the

general dimensions are shown. A CTF is characterized by a flat channel floor, a convergence

of 3:1 and a divergence of 6:1. The positioning of the piezometer taps of the heads ℎ𝑎and ℎ𝑏,

measuring devices under free and submerged flow conditions, are indicated in Figure 3.


13

Figure 3 Design parameters of a cutthroat flume (Skogerboe et al., 1973)

The advantages of a CTF are:

- The ease of construction and installation on already existing channels.

- Usage under free and submerged flow conditions.

- A smaller head loss is required in comparison with other flumes. This can be useful if

the velocity and the pressure head in the channel are low.

For other flumes free flow is assumed. Their structure favours a perfect inflection. The CTF

allows discharge calculation under both free and submerged flow. Under free flow conditions

the water profile upstream is only controlled by the water height upstream:

𝑄 = 𝐶1ℎ𝑎𝑛1 ------------------------------------------------------ (1)

(Q flow rate in mᶟ.s¹־, 𝐶1 = 𝐾𝑊1.025free flow coefficient, ℎ𝑎 the piezometric head before the

neck, 𝑛1 free flow exponent, correlated with flume length L)

The free flow coefficient is depending on the neck width W and the flume length according to

the following relation (with 𝐾1 the flume length coefficient, correlated with flume length L):

Submergence occurs when the head downstream is sufficient high to control the discharge as

well. For evaluating the degree of submergence the ratio of the downstream and upstream head


14

is used; 𝑆𝑡 =ℎ𝑏

ℎ𝑎⁄ (Skogerboe et al., 1967). The relation between the parameters

𝐾, 𝐾1, 𝑛1, 𝑛2 and 𝑆𝑡 can be deduced from Annex I (Graph IA and IB); (Skogerboe et al., 1973).

Very high submergence ratios give less reliable discharge results. At ratios higher than 95%

significant errors in discharge calculation will result from particular small reading errors from

the measuring rods of ℎ𝑎 and ℎ𝑏 , and are considered as unreliable (Skogerboe et al., 1973).

Free flow is preferred. The most important maintenance of a CTF consists of removing moss,

debris and other settlement in the flume, because they can alter the dimensions of the flume and

the flow.

Though the CTF is questioned in the field of study. Vlotman et al. (1989) remarks the scarce

amount of research on CTFs and the fact that only one specific set of dimensions for this flume

is proven to give reliable results. There is referred to the importance of the ratio between the

flume entrance and the channel width and the errors which can be induced by scale effects.

Bennett, (1972) states that CTFs with a length smaller than 3 feet (0.91m) are not reliable

anymore for submerged flow and that in general a W-L ratio within the range of [0.1-0.4] is

recommended. Manekar et al., (2007) attempted to establish a general relationship between

discharge and upstream head for CTFs under free flow circumstances. The flume length L and

width W are incorporated in the formula:

𝑄 = 𝐶𝑑(23⁄ )

1.5√𝑔𝑊(ℎ𝑎)1.5 -------------------------------- (2)

𝐶𝑑 = 1.6894(ℎ𝑎

𝐿⁄ )0.2053 ------------------------------------ (3)

Temeepattanapongsa et al. (2013) generalized the 𝐶𝑑 and 𝑛1 of equation (1) for the 24 standard

sizes of CTF, so they can not only be applied on this 24 sizes, but within the ranges of them, by

fitting them in an empirical model; equation (4) and (5). So these equations are applicable for

a CTF 0.457-2.743m length and with a 𝑊 𝐿⁄ -ratio of 1 9⁄ − 49⁄ .

𝐶𝑑 = 0.036 + 2.058(𝑊)0.97 -------------------------------- (4)

𝑛1 = 1.514(𝐿)0.021(𝑊)−0.027 ------------------------------ (5)

They evaluated equation (1), (4) and (5) as well as equation (2) and (3). They confirmed that

equation (2) and (3) is preforming well, but the accuracy of equation (1), (4) and (5) is better

with a maximum and average discharge error of, respectively, 4% and 2,2%

(Temeepattanapongsa et al., 2013).


15

2.2.3 Efficiency in irrigation networks

Along the irrigation channels, over the parcels and until reaching the root zone water losses

occur and low efficiencies are the consequence. A distinction is made between efficiency of

conveyance, distribution and field application. Conveyance efficiency differs strongly between

irrigation networks and a lot of parameters need to be taken into account. A range of 10% loss,

as average over 5 evaluated good condition channels in Spain (Krinner et al., 1994), to 40%

seepage only loss, in the alluvial planes in Asia (Plusquellec, 2002; via Asghar et al., 2011) is

found in the literature. The most important losses are due to seepage and management (Krinner

et al., 1994). Evaporation has a less significant contribution. So mentions Krinner et al., (1994)

and average of 0.5%, within the range of 0.2-1.1% water loss due to evaporation. But this cannot

be generalized since it depends strongly on the width and length of the channel, the air humidity

and ambient temperature. Infiltration losses are reported by Brouwer et al., (1989) in Table 1,

although these are only indicative values and under the assumption that lined channels are in

good condition.

Table 1 Indicative conveyance efficiency in irrigation channels (Brouwer et al., 1989).

Earthen Channels Lined Channels

Soil Type Sand Loam Clay

Channel Type

Long (> 2000m) 60% 70% 80% 95%

Medium (200-2000m) 70% 75% 85% 95%

Short (<200m) 80% 85% 90% 95%

Asghar et al., (2011) discussed the phenomenon of ‘hotspots’, certain locations in earthen

irrigation channels, where large water losses occur. On average 50% of the seepage losses were

attributed to these hotspots, covering 1.7% of the channel network, observed in several earthen

channels of a range of different soil types, in the south of Australia. The contribution of

management to conveyance efficiency can be interpreted very broad, going from vegetation,

debris or other disturbances in the channels to damage in lined channels.

There is not an unambiguous definition for distribution efficiency. According to Bos and

Nugteren, (1990) it is the efficiency of the water distribution channels and conduits from the

conveyance network to the individual fields. It can also be regarded as a measure to express the

distribution uniformity over the field (Brouwer et al., 1989; Rogers et al., 1997; Burt et al.,


16

1997). In this research the conveyance network will be considered from the BT until the inlet

to the farmers field. It is important to take into account the water losses that occur in every

bifurcation step in the network e.g. from main channel to secondary and tertiary channels. The

efficiency related to the distribution over the width of the parcel is considered as part of the

application efficiency.

The majority of the field application methods of irrigation water in the highlands of Peru is

done by surface-, specifically border irrigation. A general lay-out of border irrigation is

represented in Figure 4 (Wyseure, 2014). The water can flow via the gates from the

transportation channel towards the distribution curve were it is spread out over the width of the

parcel, to run slowly according to the slope.

Figure 4 General lay-out of border irrigation (Wyseure, 2014).

The application efficiency depends mainly on the shape, size, length, slope and roughness of

the plot, expression of the distribution curve (Figure 4), the cut-off time and the inflow rate.

Most of the efficient parameter relations are non-linear and thus optimization is possible. So

modelled Khanjani and Barani, (1999) an optimal application efficiency of 91% for a 50m plot

length, an inflow rate of 0.20 l.s¹־.m¹־ and a cut-off time of 410 min. Alazba and Fangmeier,

(1995) observed a variation of 59-80% application efficiency for different values of certain

parameters. A value of 60% can be assumed if no specific optimizing of the farmers field and

water application conditions are considered (Brouwer et al., 1989), what is mostly the case for

small-holder irrigation systems in the highlands of Peru.


17

However, not only the infrastructure and irrigation techniques play a role in defining

efficiencies or assigning losses. Gilot et al., (1997) observed in an irrigation network in the

Sierra of Ecuador that farmers in many cases prefer to say that water is lacking instead of

admitting problems exist in the social structure of water sharing. Therefore it is necessary to

take distribution rules and the interaction between water users into account, while discussing

water losses and performance within an irrigation organisation. More general, improvements of

existing irrigation networks and infrastructure will not be the only key for better production or

a more sustainable agriculture (Kastelein, 1998). Besides low performing infrastructure or

irrigation techniques also channel interruptions because of infrastructural works, passing a turn

to save money, lower theoretical water volumes than the authority gives at the entrance of the

main channel and water robbery are only some of the possible reasons of water losses (Gilot et

al., 1997; Vos, 2002; ANA, 2014). On the other hand observed Vos, (2002) in larger irrigation

commissions at the north coast of Peru, that robbery and illegal practices within WUAs even

could improve efficiencies. At the scale of the irrigation commission it are no losses of water

and it drives the water users to pay more attention if the amount of water and the hours that they

get are indeed the same as what they pay for.

Though several authors noticed the relative character of water efficiency and losses (Willardson

et al., 1994; Lankford, 2006; Perry, 2007; Pereira et al., 2012; Lankford, 2012; Boelens and

Vos, 2012). In fact real water losses never occur and it depends from which perspective the loss

is considered. E.g. water lost in the root zone via deep percolation could recharge aquifers that

contribute to springs or rivers, and thus to water users, downstream; water evaporation could

increase air humidity and enhances cloud forming and rainfall later on. From this point of view

Pereira et al., (2012) state that only water coming in contact with saline water can be considered

as a real loss, since it cannot be used anymore for most crop production or an average household

consumption. It depends which scale is regarded how a water loss can be defined. Lankford,

(2012) considers all possible scales as nested units and delineated them in Table 2.


18

Table 2 Boundaries within basin and irrigated water systems (Lankford, 2012).

In our research one commission within the río Grande catchment is considered as the system

where water losses are determined. However if deep percolation losses contribute later to río

Grande they can still be useful for commissions downstream that belong to the same WUA.

Also warn recent authors for the use of the unilateral definition of ‘Water Use Efficiency’, since

it is seen from a narrow perspective on agronomy. There is stated that efficiency indicators have

to be adapted to the purpose they will be used for (Trawick, 2001; Lankford, 2006; Boelens and

Vos, 2012). If water policy focusses too much on productivity and efficiency local water

management can be buried by new imposed norms, like ‘efficiency certificates’ discussed by

(Boelens and Vos, 2012), especially if in practice technical support is not provided.

2.2.4 Supporting framework and institutions

The Agrarian Reform in Peru was implemented in 1969. Land redistribution took place and

most of the haciendas were converted to cooperatives. In particular in the region of Cajamarca

the Rondas Campesinas2, literally peasant rounds, were founded in the seventies, and spread

out towards the south. Later they became officially recognized. The Agrarian Reform was also

associated with a radical change in water politics; La Ley General de Aguas (Decreto Ley

17752), the new water law was approved, discarding the former toma libre, free right to take

and use water for irrigation purposes. Water became officially state property and public domain,

and people could achieve irrigation water by paying a licencia, permanent-, or a permiso,

temporal access to water. These were based on the Plan de Cultivo y Riego, that defined how

2 Autonomous and democratic organs, consisting of farmers of their own community, that have the role of keeping justice and defending their lands.


19

many water somebody can get according to the irrigated area. Also the Administración Técnica

de Distrito de Riego (ATDR), the institution that managed the water distribution to every farmer

unit, was established (Vos, 2002). Despite the good objectives this system was being abused

because of its top-down nature. Driven by the economic crisis at the end of the eighties, the

Irrigation Management Transfer3 (IMT) was applied in Peru in 1995 (Tapias, 2001). WUAs,

the organs in which the water users themselves would assemble and would manage the

financial, technical, material aspects of the operation and maintenance of the irrigation system.

In the end of the 20th century frustration escalated about the centralized responsibility at national

level, what made it difficult to manage water distribution in catchments over the whole country.

In 2003 the establishment of regional governments led to transfer the power to the departments.

In 2008 three institutions; Autoridad Nacional, Administrativa and Local del Agua (ANA, AAA

and ALA) replaced the former ATDR, at respectively national, regional and catchment level.

In the same time the law of the water resources was implemented. The new ideas about the

Gestión de los Recursos Hidricos en el Peru are bundeld in the ‘Plan Nacional de Recursos

Hidricos’(Toledo Parreño, 2008). ‘Water is a limited resource’ is the main incentive. The

intention is to have a multidisciplinary legislation about water resources, so with the

involvement of the other governmental institutions. The decentralisation is not only expressed

in the shift from national to local level, but also from the coastal to the other geographical zones

of the country, the Sierra and the Amazonia. Formerly, the attention regarding irrigation

management was grown towards the coast of Peru since there the most commercial cultivations

are situated. Now there is a management plan per catchment and its organisation is elaborated

by the AAA, ALA and WUA’s. The río Grande and río Mashcón belong to the AAA Marañon,

and the ALA of Cajamarca province (ALA-C). All the AAAs of Peru are shown in Figure 5.

To avoid and rectify the fact that the irrigation management structure would be copied from the

coastal area an extra program was launched by the Ministry of Agriculture (MINAG) to

strengthen the WUAs in the highlands, with the focus on capacity building and training;

Programa Subsectorial de Irrigaciones (PSI) Sierra, sponsored by the World Bank. The

investments in PSI Costa stopped in 2009 with US$ 95 million and PSI Sierra started in 2010

with a first grant of US$ 48.33 million (Chinarro et al., 2011). 12 WUAs in the highlands were

selected to get workshops, financial and technical support to improve their irrigation systems.

Three of them are situated in the Cajamarca province including the Junta de Usuarios de Río

3 “Transfer of responsibility and authority for irrigation system management from government agencies to water users associations, or other private sector entities” (FAO, 2001)


20

Mashcón (JURM). PSI Sierra is divided into 4 main components that summarize their

objectives (MINAGRI, 2015):

- Component A: Modernization and improvement of the irrigation systems

- Component B: Technifying of the irrigation methods

- Component C: Institutional strengthening and support of the WUAs

C1: Capacity building and coaching of the WUAs

C2: Assistance for farmers with the usage of technical irrigation

- Component D: Water rights

D1: Formalization of the water rights, assigning water licences.

D2: Administrative registration of the water rights, the water licences and

nominative certificates

D3: control and water measurement works for irrigation blocks

Figure 5 Demarcation of the AAA’s in Peru according to hydrological units (Pinto Ortiz, 2008)


21

2.3 Mining practices of MYSRL and impacts on natural hydrology

In 1993 the goldmine MYSRL has settled in the province of Cajamarca. It concerns, a venture

of Newmont Mining Corporation (Colorado) with Buenaventura (Peru). The World Bank also

has 5% of the investment. MYSRL started in 1982 with exploration and in 1993 with

exploitation on 19km in straight line distance, in the north of the city Cajamarca; visible in

Figure 1. The company extracts as main ores gold and silver. At present, the running project

covers 16,000ha out of 172,500ha mine concessions, for which MYSRL owns exploration and

development rights (International Mining, 2011). This current mine district is located on the

divide of the 3 catchments: Llaucano, Crisnejas and Jequetepeque. The two first drain towards

the Atlantic while the latter towards the Pacific. It is the source area of five important rivers in

the province of Cajamarca: Porcón, Grande, Rejo and Honda. Apart from their importance

downstream, their springs are also a priority of the living communities in the direct

surroundings of the mine. Except from irrigation, the water in the channels and springs is also

used for cattle, and in some cases even for human consumption (Edwards, 2000; Golder

Associates Ltd., 2002; via Stratus Consulting Inc., 2003). According to the annual reports of

MYSRL, 9,330 farmer families are living in the environment direct influenced by the mine

(Sosa and Zwarteveen, 2012).

In Figure 6 the mining district of MYSRL is represented. The catchment divide is shown in

orange. The operations take place in five main zones: Maqui Maqui, Chaquicocha4, Yanacocha,

La Quinua – El Tapado and Cerro Negro. They represent 13 open pits, 9 rock residue heaps

and 4 lixiviation piles (MYSRL, 2011). All open pits knew several extensions after their first

exploitation.

4 Including the former open pits of Carachugo and San José


22

Figure 6 Mining district of MYSRL with indication of different open pits, discharge outlets, neighbouring

irrigation infrastructure, hydrology and the catchment divide.

The required mineral is extracted as follows: The ore containing hill is excavated and the rock

material dumped on the lixiviation pad. This pile is several times sprayed with a solution of

cyanide, in order to dissolve the minerals. If this solution is not mineral-concentrated enough it

is upgraded with active carbon. Afterwards it is channelized to the process plant where the

minerals get separated from the cyanide. This recuperation of the mineral, the so called ‘Merill

Crowe’ process, is basically a precipitation with zinc. The minerals are separated from zinc

through vaporization, induced by very high temperatures, and washing. Finally casting and

refinery takes place. The largest proportion of water is used in the lixiviation step, although

blowing up of dust, the active carbon adsorption, the Merill Crowe process and in the refining

phase also require a significant continue water supply. The net water consumption in the 3 latter

steps are given in Table 3. These data are facilitated in 2006 by Ir. Wilton from MYSRL and

are obtained via Yacoub López and Cortina Pallás, (2007). Water leached in the lixiviation

process is, in the EIA of 2006 (MWH Perú S.A., 2006), estimated to be 10-14 l.hr¹־.m²־, with

a residence time of the ores on the lixiviation pile of about 70 days. An estimation of the surface


23

of active lixiviation piles is difficult to make and changes during the exploitation of the different

open pits. According to Reichardt, (2008) the total leaching area covers 2.7 km², after the

completion of the facilities of Carachugo Stage 9 and Cerro Yanacocha Stage 4. Knight Piésold

Consulting, (2015), a company that elaborated several construction works in the MYSRL’s

mining zones, states that the total constructed surface of leaching piles is 10 km².

Table 3 Net water consumption in the Merill-Crowe process, the activated carbon columns and the casting of

MYSRL in 2006 (Yacoub López and Cortina Pallás, 2007)

Process Volume (mᶟ.year¹־) Discharge (lps)

Merill-Crowe 11 000 0.35

Activated Carbon columns 638 000 20.00

Casting 1 700 0.05

In the annual report of 2009, MYSRL claims that 98% of the used water effectively is recycled

and reused (Sosa and Zwarteveen, 2012). Yacoub López and Cortina Pallás, (2007) state that

this percentage is 95%. Also the volumes and discharges given in Table 3 are expressed as the

net water consumption, so the small proportion that is not recycled. MYSRL (2011) states that

its net consumption is 2 Mmᶟ or 63.42lps. The permit to withdraw groundwater from the open

pits is 575lps (MYSRL, 2011; ALA-C, 2013). This can be confirmed by Yacoub López and

Cortina Pallás (2007) that remarked a number of 20-30 pumping wells with all a permit of water

usage of about 25lps. The main intention of the groundwater withdraw, however, is to keep the

open pits dry for rock removal. The excess of pumped subterranean water and rainwater in the

wet season is discharged via one of the outlets of the mining zone. These outlets are indicated

in Figure 6 and their characteristics in Table 4, provided by Grufides, (2012). The mean

discharge is defined but the amount of water discharged in the wet season is logically larger

than in the dry season.


24

Table 4 Main characteristics of the 12 outlets of MYSRL mining zone and their receptor water bodies (Grufides, 2012)

Besides the water quantity that the mine requires for its operations, it alters also the natural

distribution over the water bodies. A system approach can be carried out to understand better

the broad lines of possible changes. Part of the precipitation that would fall on the surface of

the MYSRL area does not follow the natural hydrology, because it is captured, possibly used

in the mining operations, treated and drained to one of the outlets; Table 4. Groundwater

hydrology needs to be taken into account as well: most of the open pits reach a depth of about

Nr. Regime Annual

Volume

(Mmᶟ)

Mean

discharge

(lps)

Receptor

body

Type

receptor

Discharge

receptor (lps)

1 Continue 1264.8 40.1 Honda Brook 64.7

2 Continue 9486.0 300.8 Callejón River 126.9

3 Continue 15810.0 501.3 Encajon Brook 18.6

4 Intermittent 1581.0 50.1 San José Brook 28.7

5 Continue 13596.6 431.2 Shillamayo Brook -

6 Intermittent 1106.7 35.1 San José Brook 31.3

7 Continue 79.1 2.5 La Pajuela Brook 33.7

8 Intermittent 685.1 21.7 Llagamarca Channel -

9 Intermittent 1707.5 54.1 Encajon

Collotan

Channel -

10 Intermittent 1855.0 58.8 Quishar Channel -

11 Continue 1264.8 40.1 Tual Channel -

12 Intermittent 2500.0 79.3 Reservoir

San José

Channels -

13 Intermittent 1264.8 40.1 Ocucha

Machay

Brook 21.1

14 Intermittent 1264.8 40.1 Amacocha Brook 19.1

15 Intermittent 9486.0 300.8 Chaquicocha Brook 14.8

16 Intermittent 1897.2 60.2 La Shacsha Brook 11.5

17 Intermittent 632.4 20.1 Colorado River 50.6

18 Continue 1581.0 50.1 San José Brook 31.3


25

300m beneath the natural topography (MWH Perú S.A., 2006), until 500m maximum (MYSRL,

2010). To keep efficient operations going, these pits are continuously dewatered of inflowing

water from aquifers. This causes a large pumping cone of the groundwater table and therefor a

decrease in volume of aquifers, as natural reservoirs. Above all disappears the recharge of

groundwater that would normally infiltrate in the mining district of MYSRL and so the supply

of springs (Preciado Jerónimo, 2011; via Lust, 2014). The extent to which this could influence

significantly a lowered groundwater table is not mentioned in one of the EIAs of MYSRL. A

complete inventory of the existing water sources from springs, their discharge and their

quantified usage for local communities has never been carried out. The EIA of 2006 (MWH

Perú S.A., 2006) of MYSRL mentions that the distribution over the different outlets is in

compliance with the natural distribution of water over the different catchments. However there

is also stated that no measures are and will be taken to remedy changes in the phreatic water

level. So especially the people living in the proximity of the mining district are confronted with

a strong allocation of their water sources (Urteaga, 2011; via Lust, 2014; Sosa and Zwarteveen,

2012). In 2012 only 68% of the population within the department of Cajamarca had a durable

access to clean water. This percentage belongs to the 25% of Peruvian population that has the

most difficulties with water resources (INEI, 2012). This issue is confirmed in the objectives of

MYSRL’s water management where is mainly pointed out to increase the discharge in the dry

season for agriculture downstream, through pumping up, using, treating and discharging

groundwater out of the open pits as well as through collecting rainwater in the wet season to

discharge it in the dry season (MYSRL, 2011). An extra complexity factor are the different

stages over the total lifetime of the mine. We can consider exploration, exploitation of different

pits -all with another speed and efficiency-, closing phase – a slow diminishing of operation-

and rehabilitation. MYSRL distinguishes a temporal, progressive (2000-2017) and final closure

(2017) (SVS Ingenieros S.A.C., 2010). So different amounts of water are used in space and

time. It is difficult to investigate the exact hydrological alteration because no baseline studies

has been worked out before the starting of the operations in 1993 (Yacoub López and Cortina

Pallás, 2007). More than 10 years later an extensive description of the geology and subterranean

hydrology was published in ‘Informe de Aguas Freáticas en el Emplazamiento’ (Lorax

Environmental, 2004).

Apart from groundwater more water sources have to be addressed to keep the mining operations

going. Nearby lakes are exploited and, where possible, water rights are negotiated and bought

from local communities and irrigation committees. In many cases this has led to strong tensions


26

with the local people. For instance 4 channels of the community of Combayo (8km in straight

line distance downstream of Chaquicocha, with as main water contributors the brooks

Ocuchamachay/Arnemacocha, Huascar and Chaquicocha; Figure 6) have lost their sources,

resulting in 1000 affected irrigated has. This has led to escalated protests against the expansion

of the Carachugo pit (Figure 6), that required the exploitation of the community’s nearby lakes.

Although the Chaquicocha pit became a fact and the mine’s promised a profound study of

hydrological reinforcement in the catchment, the community is still waiting for a solution of

their desiccated water sources. Another issue is the construction of the San José reservoir

(Figure 6 and Table 4: Number 12). It became only a fact after persistent complaints of strong

flow reductions in two brooks, supplying 5 irrigation channels. The reservoir has been built to

store treated wastewater and capture rainwater to provide these farmers. As payoff the irrigation

committees had to give up their water rights and accept that MYSRL became responsible for

the supervision, provision and distribution of the water from the reservoir. According to Sosa

and Zwarteveen (2012) there is no involvement whatsoever from the water authorities in terms

of instructions or inspections. These and several other incidents with neighbouring communities

and committees have taken place over the years. In all the cases the impact on their water

resources was not mentioned in the EIA of 1998.

2.3.1 Dam río Grande

Callejón and Encajon, two of the outlets of the MYSRL mining district (Number 2 and 3; Figure

6 and Table 4) are the two main brooks that form the río Grande. About 6km downstream a

dam is constructed on the river, constructed in 2003-2004, originally for sedimentation

purposes. After complains of the irrigation commissions and river offtakes for other purposes

MYSRL agreed with ALA-C upon controlling the discharge from the dam into the río Grande

downstream, so it does not fall under 500lps. The reservoir has a capacity of 400,000mᶟ

(MYSRL, 2011). MYSRL states in the evaluation of their water management to have

contributed to a larger discharge in the río Grande, e.g. in 2008, 2009 and 2010, respectively

88, 50 and 49lps additional to the base flow in the dry season (MYSRL, 2011).


27

3 Materials and methodology

3.1 Study Area

3.1.1 The Grande de Mashcón catchment

In Figure 7 the río Grande and its main contributors are represented. The main sources are

situated in the open pits, or at least within a distance of 2km, of the Yanacocha mine. Beside

those, the tributary Purhuay also plays an important role. The JURM, the WUA of the Mashcón

catchment, is in charge of the management of irrigation supply of the río Grande. In the

Mashcón catchment 77 committees and 8 commissions are registered. The commissions are

Atunmayo, Lluscapampa, Vizcaches and Tres Molinos, and their offtakes are indicated on

Figure 7. They pay respectively for water licenses of 60, 60, 20 and 100lps. The committees

are located more upstream of the río Grande and depend on the water supply by springs. They

all have water licenses of less than 10lps. Close to the BT of Lluscapampa there is an offtake

of EPS Sedacaj S.A., a water treatment plant for potable water for the city, with an acquisition

of 200lps. A similar offtake is based on the río Porcón. The JURM is one of the 12 selected

WUAs for PSI Sierra, for the components A, B, C1 and C2 (2.2.4).


28

Figure 7 Nomenclature of the hydrology of the río Grande. Offtakes 1: Tres Molinos 2: Vizcaches 3:

Lluscapampa 4: EPS Sedacaj S.A. 5: Atunmayo

3.1.2 Tres Molinos

The commission Tres Molinos (TM) is the last BT on the río Grande before it confluences with

the río Porcón into the río Mashcón; Figure 7. The BT is situated on a height of 2800m asl. The

main channel is positioned around the hill Rosario Horco until a height drops, where it runs

into the valley. The structure of the irrigation network is asymmetric, shown in Figure 8. The

first irrigated parcels, enclosed between the main channel and the río Mashcón, are mostly

tomas directas, parcels directly connected on the main channel, or relatively short secondary

channels. The first important secondary channel is Shilla which is divided in Shilla Alta,

situated on the knolls next to Rosario Horco, and Shilla Baja, the transition of the knolls to the


29

valley. The two following secondary channels are relatively longer and describe a pathway from

the high main channel into the valley: Los Alpes and Tres Molinos. The latter covers the most

space in the valley. After the offtake of the secondary channel Tres Molinos and the large height

drop, it divides in two. The first tertiary channel supplies Unión Cajamarca, Carolina and

Ayllus. The second tertiary channel consists of El Triunfo, Los Mercedes and El Prado. The

total irrigated area of TM is 265ha and 244 different farmer or farmer units. However there is a

large difference in the parcel size per farmer unit. The mean area of a parcel is 1.09 ±3.26 ha,

but there are six extreme large ones with respectively 11, 12, 16, 20, 26 and 30 ha. 32% of

farmer units are tomas directas. But in percentage of the total area this is lower since these six

largest parcels are situated in the valley and so in the laterals of Tres Molinos or Los Alpes. The

length of the main channel is 5.1 km, of which the last 200m recently has been laid in concrete,

realized by PSI Sierra.

Figure 8 Schematic representation of the irrigation network in the commission Tres Molinos. Distances (measured

in Q-GIS), starting from the bocatoma are indicated in km. The main channel is marked in orange. The names of

the main secondary and tertiary channels are indicated. Route indication of conveyance and distribution efficiency

measurements in the main channel (dark green), secondary and tertiary channel of Tres Molinos and El Triunfo

(light green).


30

Just after the BT a control structure is installed in 2013, as well within the project of PSI Sierra.

In the work ‘Mejoramiento del servicio de Agua del sistema de riego channel Tres Molinos, en

la localidad de Tres Molinos, distrito de Banos del Inca, provincia de Cajamarca, region de

Cajamarca’ the ‘Oficina de Gestión Zonal Norte, Chiclayo’ elaborated the design of a

rectangular CTF; shown in Figure 9. This flume-type has similar sizes as the 0.61m x 1.83m

(24inch x 6feet) version (Annex I, Graph IC), discussed by Skogerboe et al. in 1973. However

a measuring rod has never been placed, so this control structure is not yet in use. Other

improvements of the irrigation infrastructure are also planned or already elaborated, among

others lloraderos5, dissipator ponds, drop structures and culverts.

Figure 9 Rectangular cutthroat flume in Tres Molinos within the project of PSI Sierra

According to the ‘Plan de distributión del agua 2014’ of the JURM, is at least 80% of the area

under irrigation cultivated with pasture as forage crop. Of the area included in the survey (3.6.1),

more than 96% is hereto dedicated. Potatoes, maize, alfalfa, roses, hortensias (Hydrangea) and

other vegetables cover the other small proportion of the cultivated area. They are mostly

cultivated for personal consumption and not on a commercial basis.

The populated centres in the TM are Chinchimachay, Moyococha Shilla, Tres Molinos, Santa

Barbara and Venecia, as indicated in Figure 11.

TM has a license of 100lps. This discharge is per week divided over the total amount of irrigated

area, which corresponds to 227.6 mᶟ.ha¹־ or 22.76 mm. Every farmer unit gets a certain amount

of hours according to the amount of hectare he has to irrigate and respectively pays for the total

5 Putlog hole in a lined channel that allows surplus water from higher elevations to drain into the channel


31

amount of water in this time. In Annex II (Figure IIA) the official document is shown that

determines the order of irrigation. The survey (3.6.1) made clear that especially in secondary

channel of Shilla there are problems in the exact division of the water. When the turn of Shilla

Alta and Baja starts every Sunday, all the people of these secondary channels are present to

claim their share of the water. A fixed schedule and monitoring is lacking, which results in

tensions between farmers and families.

Geology and Pedology

An intercomparison and evaluation between geological literature of the region (Vásquez and

Crisólogo Rodríguez, 2009), soil determinations (Landa et al., 1978), landscape morphology

and GIS interpretation of several shape-files provided by the ZEE6 Cajamarca is carried out and

verified with field visits and interviews of the local peasants (survey in 3.6.1). The considered

soils of TM are listed op in Annex III (Table IIIA). The soilscape is characterized by four

representative soils indicated in Figure 10.

Figure 10 Soilscape classification of Tres Molinos

6 the department of spatial planning within the regional government


32

The soils represented by Soil 1 (Figure 10) have parent material from fluvio-alluvial deposits

originating from the Pleistocene and Holocene. The river has sufficiently incised, so these soils

are significant higher located and are not inundated anymore during the wet season. The texture

is heavy due to alluvial clay lens deposits. These Quaternary sedimentary deposits are lying on

light to medium texture debris from older and different origin. The soil profile consists of a

thick mollic horizon (+-30cm) with high organic matter content, loamy texture (silty clay loam)

and a gradual transition to AB and B with increase of mineral and clay illuviation (Stefan and

Stefan, 2012). The occurrence of a AB or 𝐵𝑤 horizon is possible because of mixing due to

swell- and shrinking, what inhibits slightly the gradual illuviation. Secondary carbonates are

supposed to be leached out in first 0.50-1m, caused by the strong rain events in the wet season.

So the pH would increase in depth. Also grey- blue mottled spots, pseudo-gley, can be present

due to temporary stagnant water due to the weak permeable clay layers. A high biological

activity is expected, because of the land use (pasture and extensive grazing). This soil type will

further be called the ‘Phaeozem’.

The soils that can be found in the Shilla secondary channel are indicated with Soil 2 (Figure

10). They are partly located on a small steep hill in between Rosario Horco in the north and the

río Mashcón in the west. The bedrock is assumed to be outcropping material from the Mesozoic,

in particular the Farrat formation, since the parent material is classified as quartzite and

sandstone and the soils are impeded by bedrock at shallow depth. During interglacial periods

and in the beginning of the Holocene softer material is eroded and transported around the knolls.

This can also explain the chromic Vertisols from fluvio-glacial origin closer to the depression

(𝑖𝐴𝑙 𝑝 𝐸 𝑙

1 𝐼 0 𝑛𝐼𝑉 in Annex III). Coarse sediment from these fluvio-glacial movements can partly be

deposited as well. In the elevation profile in Figure 11, there is a clear passage around 1500m

distance, in between the two Shilla knolls and the Rosario Horco hill in the north, where

probably material is transported towards the valley. On the steep slopes of the Shilla knolls

towards the feet, where the colluvium is heaped up, the soils are moderate profound. They are

dark coloured, due to a humic A horizon, but show mostly bright reddish brown and litho

chromic colours, because of erosion on the slopes. The texture is mostly light; sandy loam, but

a argic horizon can sporadically be present if the profiles are more developed. Throughout the

profile a large amount of gravel and rocks of various dimensions are present, with an estimated

volume proportion of 10-15%. This has an important consequence on the water amount that can

be stored in the soil and the impediment of certain degree of tillage with heavy machinery. The

reaction is slightly acidic because of the nature of the parent material. According to the WRB,


33

these soils can be classified as Lithosols, (humic) Cambisols, haplic or luvic Phaeozems or

Regosols. These soils will further be indicated as ‘Lithosol’.

Figure 11 Elevation profile from the Rosario Horco hill to the Shilla knolls

The soils in the valley are represented by Soil 3 (Figure 10). They belong to the ‘Association

of the Cajamarca valley’. They are formed in the interglacial periods of the Pleistocene or

beginning Holocene by the erosion and transportation of tertiary and secondary material from

the melted glaciers and deposition in the depressions and valleys. Especially fine clayey

material is eroded from the weathered basic rocks, especially limestone, of the surrounding

hills. Hence these soils are from fluvio-glacial or lacustrine origin and have a more alkaline

character. It are profound soils with a A/𝐵𝑤 or A/𝐵𝑡 profile, with moderate to strong clay

illuviation in depth. Because of the heavy texture drainage is bad. In the wet season this can

result in water stagnation or slight waterlogged soils if no drainage measurements are taken. In

the dry season the soils are hard and can show cracks due to the swell and shrink mechanism.

In the FAO soil taxonomy these soils correspond to gleyic/ luvic Phaeozems or pellic/ chromic

Vertisols. They will further be indicated by ‘Vertisol’.

The soils, indicated as Soil 4 (Figure 10), are positioned in the end of the main channel and on

a higher elevation than the valley. They are developed on volcanic tuff (origin Huambos

(Vásquez and Crisólogo Rodríguez, 2009)) mainly consisting of unconsolidated reddish

sandstone. On elevations higher than TM, coarser agglomerate and pyroclastic rocks are

probably present and the soils are mainly tending to the less developed, very superficial d1-

soils (Annex III). The d2-soils are not developed on pure volcanic material. Landa et al., (1978)

state that these d2-soils are mainly of volcanic parent material but there can exist mixtures with

colluvial material or other coarse debris of fluvio-glacial deposits or moraines. Due to this


34

conjunctive origin the texture is medium instead of the light texture of d1-soils. The

development of the soil ranges from very superficial and weak with profile of less than 30cm

(d1 and d2) to moderate superficial with a profile 30-60cm (d2). The light texture of the d1-

soils results in an excessive drainage. According to the WRB, this soil can be classified as a

thapto-andic or arenic Regosol, Andosol or Leptosol. The reaction is neutral to light acidic

which confirms the nature of the volcanic tuffs. These soils are situated on slopes of about 25%.

The low coherence in the matrix material makes them on these slopes prone to erosion. They

are very superficial and therefore difficult to treat with machinery. Vegetating these soils,

enhances the coherence of the matrix and makes them less susceptible for erosion. The d2-soils

on the other hand have a good water regulation. Because of the medium texture and the relative

smaller slopes of about 13% they have only a small erosion risk. These soils are suitable for

more intensive cultivation and there are no restrictions for machinery. They can be classified

as mollic Andosols or eutric Regosols (Landa et al., 1978). The neutral to alkaline reaction of

both determined soils can be explained by volcanic loess deposition. They will further be

indicated as ‘Andosol’.

3.2 Agrometeorological data

For the case study in TM agrometeorological data from the Augusto Weberbauer station (AW)

are used. This station is situated on the UNC campus in the valley in between the city of

Cajamarca and Baños del Inca, and the height difference with TM is maximum 200m. Data of

other nearby and relevant meteorological stations, represented in Table 5. This data can be

useful for other case studies in neighbouring catchments.


35

Table 5 Meteorological stations of Senamhi nearby the city Cajamarca. Tmax: maximum temperature; Tmin:

minimum temperature; RH: relative humidity; prec: precipitation; Ea: actual atmospheric pressure; VMS: wind

speed; Wind dir.: wind direction; WBT: wet bulb temperature; DBT: dry bulb temperature; between the brackets

the number of point measurements within one day are given

Name Station Altitude Coordinates Variables Timespan data

El Ronquillo 3313m 7°9’– 78°32’ Tmax, Tmin, RH, prec, Ea, VMS, Wind

dir.

2010-2015

Granja Porcón 3150m 7°2’- 78°38’ Tmax, Tmin, RH, Rad, VMS 1978-2010

Tmax, Tmin, RH, prec, Ea, VMS, Wind

dir.

2006-2012

3260m 7°2’- 78°37’ Tmax, Tmin, WBT(3), DBT (3), prec

(2), VMS, Wind dir.

2010-2014

Bambamarca 2577m 6°40’- 78°31’ Tmax, Tmin, RH, Rad, VMS, Evap 1978-2010

Tmax, Tmin, WBT (3), DBT (3), prec

(2), VMS, Wind dir.

2009-2014

3400m 6°41’- 78°27’ Prec (2) 2009-2014

Namora 2782m 7°12’- 78°20’ Tmax, Tmin, WBT (3), DBT (3), prec

(2), VMS, Wind dir.

2010-2014

La Encañada 2950m 7°7’- 78°19’ Tmax, Tmin, WBT (3), DBT (3), prec

(2), VMS, Wind dir.

2010-2014

San Juan 2469m 7°17’- 78°29’ Tmax, Tmin, WBT (3), DBT (3), prec

(2), VMS, Wind dir.

2010-2014

San Pablo 2100m 7°5’- 78°50’ Tmax, Tmin, WBT (3), DBT (3), prec

(2), VMS, Wind dir.

2010-2014

Llapa 2900m 6°59’- 78°49’ Tmax, Tmin, WBT (3), DBT (3), prec

(2), VMS, Wind dir.

2010-2014

Asunción 2194m 7°18’- 78°29’ Tmax, Tmin, WBT (3), DBT (3), prec

(2), VMS, Wind dir.

2010-2014

San Miguel 2560m 6°59’- 78°51’ Tmax, Tmin, WBT (3), DBT (3), prec

(2), VMS, Wind dir.

2010-2014

Celendín 3050m 6°51’- 78°7’ Tmax, Tmin, WBT (3), DBT (3), prec

(2), VMS, Wind dir.

2010-2014


36

3.2.1 Precipitation analysis

There are two precipitation datasets of AW available from Senamhi; 1934-2010 and 2000-2014.

The first mentioned are daily cumulative data and the latter from an automatic DAVIS data

transfer at 7am and 7pm. Between the two datasets there is an overlap of 10 years. Plotted

together, they do not show significant deviations in these 10 years. For the exploration and

analysis of the precipitation the datasets (1934-1999 and 2000-2014) are merged. In Graph 1

the cumulative annual precipitation (in mm) of this dataset is shown. There is a clear difference

between the first decades, until ’70, and the last. This change corresponds with the installation

of the meteorological station at the UNC campus in 1973. As it is assumed that the recent

devices are more reliable, for this study preference is given to 1973 onwards series.

Graph 1 Time series of the cumulative annual precipitation (mm) 1934-2014 of the station AW (UNC and

Senamhi, Cajamarca).

The mean and standard deviations of precipitation per month, for the 1973-2014 dataset, are

given in Table 6. The standard deviations are high for precipitation data. The hydroTSM-

package (Zambrano-Bigiarini, 2014) is used as an exploratory tool to visualize the monthly and

annual time series, shown in Figure 12. The monthly boxplots correspond to Table 6. Standard

deviations are high and extreme events occur mostly in January, February, March, July, August

and September. The clear distinction between dry and wet season is visible. In Peru often the

meteorological services disintegrate series into normal years, El Niño and La Niña years. The

monthly and annual time series, are classified according to the Southern Oscillation Index

(SOI). Especially in the coastal desert a relationship exist between cyclic spatio-temporal

outliers in precipitation data and the SOI, but this is less straight forward in the highlands. At a


37

first glance the influence around Cajamarca is not so obvious; therefore this research has not

investigated the el Niño impact.

Table 6 Monthly mean and standard deviation of precipitation (mm) 1973-2014 of the station AW (UNC and

Senamhi, Cajamarca)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Mean 80.2 102.4 119.5 70.0 30.1 10.1 5.9 8.4 29.1 65.8 65.3 71.8

Sd 39.1 50.6 57.7 28.5 17.8 8.7 5.8 7.6 19.6 32.4 27.7 33.2

Figure 12 Monthly and annual representation and boxplots of the 1973-2014 precipitation time series of the AW

station (UNC and Senamhi, Cajamarca), using hydroTSM-package (Zambrano-Bigiarini, 2014)

To evaluate how precipitation is changing over time a linear and "lowess" (local and robust)

regression is elaborated, with the car-package (Fox and Weisberg, 2015) in R and is graphically

represented in Graph 2 on a scatterplot of the time series. The robust regression is necessary to

ensure that extreme values, e.g. erratic rainfall during transition to dry or wet season or ENSO-

years, have less impact on the regression. The "lowess" allows to identify the general trend,

breakpoints and changes in trends. A minor increasing monotonic trend can be observed visibly.

The non-parametric Mann Kendall-test for trends is not significant (tau=0.0157). A seasonal

trend analysis of all the individual months resulted in a significant decreasing trend for August

of less than 0.5mm over the entire period of the dataset.


38

Precipitation of the AW station is used. Within the catchment a rough increase of 29 mm per

100 m altitude can be assumed, based on the observation in the region of Cajamarca by

(Hijmans et al., 1999).

Graph 2 Scatterplot of the precipitation dataset of 1973-2014 (UNC and Senamhi, Cajamarca). Regression is

indicated through the car-package (Fox and Weisberg, 2015): black line: lowess regression; dotted line: 95%

confidence interval; grey line: linear regression

3.2.2 Analysis of other meteorological variables

In Table 7 a brief overview is given of the measured variables at the AW station. A distinction

is made between the dry and wet season to have a better insight what variables change in

between. An overall trend analysis is done over the timespan and the months with a significant

trend are indicated. The minimum temperature is slightly lower in the dry season because of

the absence of clouds in the night that cause significant lower temperatures than in the wet

season. This can as well be seen in the dry bulb temperature at 7am.

A significant decreasing trend in relative humidity is confirmed by a similar trend for the wet

bulb temperature at 1pm. A significant increasing trend in minimum temperature is more

complex to clarify. This trend occurs both in dry as in wet season months. On the other hand a

decreasing maximum temperature exists over the 30 years. More cloud formation at specific

times in the day can be a possible explanation. An overall change in humidity distribution in

height in the atmosphere can be considered. The characteristics of the wind speed-data,

available in for 1978-2010 and 2000-2014, are not mentioned in Table 7. The trend analysis


39

gave unreliable results and the two datasets deviate strongly (mean wind speed 1978-2010= 1.3

m.s2.7 =2000-2014 ;¹־ m.s¹־). It can be assumed that the wind measurements are not reliable.

This assumption can be confirmed by the lack of wind speed and direction data of the recent

datasets (2010-2014) at other locations mentioned in Table 5. This consideration needs to be

taken into account for the interpretation of the ET0 calculation in the field water balance.

Table 7 General statistics and trend analysis of meteorological variables of the AW station, elaborated in R. *

0.01< p ≤ 0.05; ** 0.001< p ≤ 0.01; *** p ≤ 0.0001. The tau of a two-tailed Mann Kendall-test is given of the

variable over the entire year. Per month significant (-) decreasing and (+) increasing trends are given.

Variable Dataset Dry season Wet season Overall trend

(tau)

Months with trend

Min temperature

(°C)

1978-2014 6.0±1.2 8.9±1.3 0.112∗∗∗ March (+), May (+), July (+),

August (+), Oct (+), Dec (+)

Max

temperature (°C)

1978-2014 22.0±0.7 21.6±0.8 −0.128∗∗∗ -

Solar Radiation

(W.m²־)

1978-2010 454.9±39.1 459.8±46.6 -0.04 March (-), August (+)

DBT (̊C) 2000-2014

7 am 7.3±1.2 10.4±0.9 0.068 -

1 pm 20.6±0.6 20.1±0.8 0.052 -

7 pm 14.5±0.5 14.3±0.9 0.079 -

WBT (°C) 2000-2014

7 am 6.3±1.2 9.1±1.0 0.046 June (+), August (+)

1 pm 11.7±1.1 12.6±1.1 −0.232∗∗∗ August (-), Dec (-)

7 pm 10.2±0.9 11.2±0.9 -0.045 August (-), Sept (-)

Evaporation

(mm.day¹־)

1978-2010 93.9±23.2 69.5±19.4 -0.07 Jan (-)

RH (%) 1978-2010 63.6±5.4 69.2±6.4 −0.285∗∗∗ Jan (-), Feb (-), March (-),

April (-), May (-), Sept (-),

Oct (-), Nov (-), Dec (-)


40

3.3 Discharge inventory Grande de Mashcón catchment

Characterization of possible discharge changes over time depends on older data. Some

inventories and monitoring projects have taken place but there is still a lack of data. The

institutions that are and were collecting data are the former INRENA (Instituto Nacional de

Recursos Naterales), the current ANA (in Cajamarca represented by ALA-C), Senamhi

(Servicio Nacional de Meteorología e Hidrología del Perú) and RENAMA (Gobierno Regional

de Cajamarca - Gerencia Regional de Recursos Naturales y Gestión del Medio Ambiente).

Except from these governmental institutions, COMOCA (Comisión de Monitoreo de Channeles

de Riego Cajamarca) is another interesting source of data. It concerns a private company that

monitors water quality and quantity in irrigation channels that could have a direct impact of

MYSRL. Besides the dubious fact that this company is paid by MYSRL, they maintain a very

open image and invite other institutions to their measurements. An analysis on the discharge

data of the monitored channels in the subarea of the río Grande is carried out and this data is

tested on possible trends, through linear regression or the Mann Kendall test for non-parametric

time series. These analyses are conducted over the months June-October, since all the

concerned channels are supplied by springs and the assumption is made that the response of

groundwater on the stop of rainfall is delayed in comparison with surface water. Finally a proxy

is used. The change in water license over time can be considered as such a proxy. The licenses

data of the committee Salvador San José de Coremayo (SSJC) are collected. This channel runs

18km down on the west side parallel to the río Grande, originating from sources of Corral

Blanco; Figure 6 and Figure 7.

3.4 Infrastructure evaluation: Flume Calibration

The CTF, present in the main channel of TM, has been evaluated. Dimension deviations from

the design are observed. In Annex IV (Table IVA) the free flow discharges for the design

dimensions, determined by the relation 𝑄 = 1,499. ℎ𝑎1.646

, are given. In Figure 13 these

deviations from the Skogerboe et al., (1973) defined proportions CTF are represented.


41

Figure 13 Deviation in dimensions in the installed rectangular cutthroat flume in Tres Molinos (grey), in

comparison with the design dimension (black)

Prior to the installation of a measuring rod and proper functioning of the CTF a calibration is

performed. Previous to the velocity measurement the channel section of the CTF is cleaned so

no debris could influence the flow during calibration. The gate of the BT is opened and closed

so different volumes could enter the main channel and three different water height stages could

be measured. It is of importance that the water height does not exceed a the limit of free flow

conditions. This is considered if the height, and so the associated discharge, are within the range

of free flow according to the design parameters. For the three water heights the velocity is

measured, according to the pulse-mode, with a OTT C2 small current meter (OTT Messtechnik

GmbH & Co. KG, n.d.) and OTT Z400 counter (OTT Hydromet GmbH & Co. KG, n.d.). The

propeller is placed at 4-decimal of the water height, as a one-point method of measurement,

which gives the best approach of the mean velocity for shallow streams with a depth of less

than 3m (Singh, 2012). Three velocities are measured per water height over a time span of 10s.

The mean velocity is calculated and multiplied by the dimensions of the cross-section. Three

such measurements are taken in the middle, at one and three quarter of the width of the channel.

The calibration measurements are processed in Excel, a power trend line is plotted on the data

and compared with the design equation and the Manekar et al., (2007) and Temeepattanapongsa

et al., (2013) approximations.


42

3.5 Efficiencies of the irrigation network

The efficiency over the main channel, the Tres Molinos secondary channel and the El Triunfo

tertiary channel is measured, over several days in September 2014. Every collection consist of

a set of discharge measurements over the route indicated in Figure 8. Every half a kilometre the

velocity is measured with the current meter and counter described in 3.4 and converted to

discharges. The methodology and number of flow measurements over the channel width are

equal to the calibration defined in 3.4. The loss in discharge is expressed per length unit of the

channel. The efficiency is used as an input parameter in the field water balance.

3.6 Field water balance

To evaluate the growth performance of the irrigated crops within TM, the field water balance

is modelled in Aquacrop 4.0. It is a model developed by the Food and Agriculture Organization

of the UN. It simulates yield response to water of herbaceous crops, and is particularly suited

to address conditions where water is a key limiting factor in crop production (FAO, 2013). The

input data for this model are climatic data, crop characteristics, management description, soil

parameters and simulation conditions. The advance of this model is that only a limited number

of variables are needed to obtain realistic results.

Different scenarios (explained in 3.6.2.3) are modelled and compared through the following

variables: biomass, biomass water productivity (WPb), biomass irrigation water productivity

(WPirr) and irrigation depth. Aquacrop displays both biomass and yield. Yield plays

specifically a role if consumable from not consumable parts of the plant need to be

distinguished, e.g. grains from leaves. Based on the survey, a maximum of 10% non-

consumable grass-types is considered in TM. This grass type is called ‘mala hierba’. In

Aquacrop yield is obtained by multiplying the biomass with the harvest index, which increases

in time. Since we are not interested in absolute yield values and the output of the variables are

only used to compare the scenarios, biomass is chosen as an indicative variable. It is expressed

in dry matter (DM) ton.ha¹־. WPb an WPirr are respectively calculated by dividing the biomass

over the water losses by the evapotranspiration and irrigation water.


43

3.6.1 Survey

To have more information for the input variables in the Aquacrop, a survey has been handed

out to farmers within the TM commission, in Annex V (Figure VA). In total 18 farmer units

participated, which covers 40% of the total irrigated area. Crop, soil and yield characteristics

and questions about water problems in the dry season are included.

3.6.2 Environment and crop

3.6.2.1 Climate

The meteorological input variables required in Aquacrop 4.0 are rainfall, ET0, temperature and

𝐶𝑂2- concentration. The dataset of 2000-2014 is used. The precipitation data is daily and the

temperatures are mean monthly minimum and maximum temperatures. 𝐶𝑂2- concentration are

default values incorporated in Aquacrop, depending on the time-series that are chosen. The

ET0-values can be slightly overestimated because of the unreliable high wind speed data,

mentioned in 3.2.2.

3.6.2.2 Crop

As mentioned in 3.1.2, pasture is considered as the main crop for the field water balance. The

cultivated crop is mostly ryegrass, but mixing with other pasture types occurs frequently. The

survey delivered the most important grass genera on average in TM: Ryegrass (Lolium): 57%,

clover (Trifolium): 18% and grama (Pennisetum clandestinum) 13%. To adjust the crop growth

cycle as good as possible to the permanent pasture cover, the crop in Aquacrop is characterized

with a short as possible growth to maximal cover of the ground, i.e. 12 days. The maximal cover

is estimated and compared with the survey resulting in 95%. A maximum effective rooting

depth of 0.85m is taken, as an average of the distribution of different grass types and based on

the FAO-values (Allen et al., 1998). In general the crop is assumed to be moderately tolerant to

water stress. The Aquacrop default for green leafy crops is moderately sensitive to water stress,

but based on Wedderburn and Pengelly, (1991) the already existing ryegrass species is

considered to be more adapted to the specific circumstances of the climate in Cajamarca and so

with the associated water stresses. Although this can be questioned because in water stress

circumstances mala hierba overgrows often ryegrass and most farmers sow after 4-5 years a

new ryegrass cultivar, according to the survey. The crop is calibrated for soil fertility stress.

Most of the farmers do not use any extra fertilizer except from the manure coming from the


44

livestock itself. The conversion factor from manure to available nutrients is less than one which

in long term results in fertility stress. One of the 12 interviewed farmers, who cultivate pasture,

uses occasionally fertilizer. Though it is only one farmer he represents 28% of the area covered

by the survey. In Aquacrop full fertility is assumed, but there is not enlarged any further on this

during the analysis of the results.

3.6.2.3 Management

The irrigation scenarios, listed in Table 8, are compared for the 4 different soil types are

compared.

Table 8 Different water supply scenarios for the evaluation of the irrigation performance in the field water balance of Tres Molinos

License Water supply according to the water right of

100lps entering the BT

Actual Water supply according to the measured

discharges entering the BT

Crop requirement Water supply necessary to avoid water stress in

the crop

In the two first scenarios once a week irrigation is applied. The crop requirement water supply

scenario assumes that water in the root zone can deplete until the limit of 95% of the readily

available water (RAW). If all the RAW would be depleted, stomatal closure would occur. In all

the scenarios conveyance and field application efficiency are taken into account. The

conveyance efficiency is assumed to be depending on the distance from the BT. All the three

scenarios are simulated in four representative regions, with therefore all their characteristic

efficiency. A loss of 5.7 lps.km¹־ is assumed, which is elaborated according to 3.5, in 4.3.

According to the distances from the BT, measured in Q-GIS and represented in Figure 8, an

average discharge loss is calculated per subarea (according to the four soil types in 3.6.2.4).

The actual discharges entering the BT in the dry season are based on two measurements (giving

84 and 87lps). A border irrigation efficiency of 60% is used according to the literature (2.2.3)

and (Brouwer et al., 1989; US EPA, 2003). This low value is also assumed since the distribution

curve (Figure 4) is during field visits observed not to be well maintained or even lacking. The

irrigation depths shown in Table 9 are used for all the scenarios.


45

Table 9 Irrigation application (in mm) for the 4 soil types in the license and actual scenario, as management

input data in Aquacrop

Soil types License

(100lps)

Actual

(85.5lps)

Phaeozem 13 11

Leptosol 11 9

Vertisol 10 8

Andosol 11 9

3.6.2.4 Soil

The four soil types represented in the section of ‘Geology and Pedology’ (3.1.2) are used in

Aquacrop. Groundwater is set on a depth of 5m, which has no influence in any of the soils.

There are some farmers that have wells to pump up groundwater as extra irrigation support. But

these sources are depleted in the dry season, according to the survey. More profound

investigation is advised needs to confirm the assumption of no contribution by groundwater.

Curve numbers (USDA, 1989) and readily evaporable water (REW) (Allen et al., 1998) are also

assigned to the soils in Table 10. The characteristics of the four soil types are listed up in Table

11-15. A stoniness (coarse gravel and inert material) of 10% in the first horizon and 15% deeper

in the profile of the Leptosol is assumed and the total available water (TAW) has been adjusted

accordingly. In this soil a restrictive layer (hard bedrock) is implemented at 0.60m depth.

Table 10 Curve Numbers and Readily Evaporable Water for the four soil type

CN (-) REW (mm)

Phaeozem 74 10

Leptosol 40 5

Vertisol 80 11

Andosol 40 5

Table 11 Soil characteristics for soil type Phaeozem

Depth

(cm)

Texture

class

PWP

(V%)

FC

(V%)

Sat

(V%)

TAW

(mm.m¹־)

Ksat

(mm.day¹־)

0-30 Clay Loam 19.9 33.7 50.6 138 284.4

30-100 Clay loam 20.7 35.0 47.6 143 123.1


46

Table 12 Soil characteristics for soil type Leptosol

Depth

(cm)

Texture

class

PWP

(V%)

FC

(V%)

Sat

(V%)

TAW

(mm.m¹־)

Ksat

(mm.day¹־)

0-20 Loamy

sand

7.0 13.0 46.3 60 1700

20-60 Loamy

Sand

6.0 12.0 44.2 60 1500

Table 13 Soil characteristics for soil type Vertisol

Depth

(cm)

Texture

class

PWP

(V%)

FC

(V%)

Sat

(V%)

TAW

(mm.m¹־)

Ksat

(mm.day¹־)

0-30 Silty Clay

Loam

23.6 39.3 51.6 157 115

30-120 Clay 30.0 42.6 52.5 126 56

Table 14 Soil characteristics for soil type Andosol

Depth

(cm)

Texture

class

PWP

(V%)

FC

(V%)

Sat

(V%)

TAW

(mm.m¹־)

Ksat

(mm.day¹־)

0-45 Loamy

sand

6.2 12.6 45.4 64 1919

3.6.3 Simulation strategy for forage crops

To define a crop in Aquacrop, one can chose between ‘Fruity/Grain producing crops’, ‘Leafy

vegetable crop’ and ‘Root and Tuber crops’. The distribution between leaf expansion, root

development and yield production is different, but all have the same growth cycle; shown in

Figure 14a. Harvest should take place in the beginning of the late season. A forage crop

however, undergoes several harvests during one season; represented in Figure 14b.


47

Figure 14a General growth cycle for crops in Aquacrop (FAO, 2013) b Typical growth cycle for forage crop (Allen

et al., 1998)

The option ‘forage crops’ is not yet provided in Aquacrop 4.0 (Vanuytrecht et al., 2014). To

overcome this deficit a comparison is made to define the difference between the following

possible simulation strategies;

- Crop rotation

- One crop cycle

This comparison validated the assumption that the crop rotation simulation is less suitable for

forage crops, due to the extra energy needed for germination, development of roots and the first

leaves, for every cutting event. The one crop cycle simulation is chosen and stress will be mostly

expressed by stomatal closure and early senescence in drier years. Though this simulation

resulted in an underestimation of stress on leaf expansion after every approximately 50 days.

For the yield formation a reduction of 10% of the simulated values, is taken into account to

have more realistic data. The justification of this simulation choice is broadly explained in

Annex VI.


48

4 Results

4.1 Discharge inventory Grande de Mashcón catchment

The commonly used discharge measurement station on the río Grande is situated just after the

junction of the brooks Haultipampa and Los Alisos and thus before the offtakes of Sedacaj S.A.

and Lluscapampa (-7°05’05”; -78°31’16”). The available discharge (in mᶟ.s¹־) data of this

monitoring point is given in Table 15. The first important series of measurements was

elaborated by EPS Sedacaj S.A. in the report ‘Estudio de Prefactibilidad para Nueves Fuentes

de Abastecimiento de Agua Potable a la Ciudad de Cajamarca año 2035’, issued in 2007, but

the measurements were done in 2002. ALA-C started in 2013 a monthly monitoring program

in 24 fixed places in the Mashcón and Chonta catchments, with the objective to initiate a

baseline study for rivers that can be influenced by Conga7. According to EPS Sedacaj S.A.,

mentioned by Benavides Ferreyros et al., (2007), the mean annual discharge in 1977-1998 in

the río Mashcón was 750lps and reached its minimum in 1992 with a discharge of 300lps.

Table 15 Available historical discharge (m³.s¹־) data of monitoring point on the río Grande

Year Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec Institute

2002 0.74 0.96 1.20 0.92 0.66 0.41 0.31 0.29 0.32 0.49 0.44 0.69 EPS Sedacaj

S.A.

2007 1.23 INRENA

2013 2.63 1.87 1.05 0.75 0.79 0.62 0.70 0.63 1.42 ALA-C

2014 1.55 2.14 2.88 1.30 1.30 0.46 0.29* ALA-C; JURM*

2014 1.63 1.05 0.89 Senamhi

2015 2.71 Senamhi

In the report ‘Inventario de Fuentes de Agua Superficial de la Cuenca del Mashcón’ of

INRENA (Benavides Ferreyros et al., 2007) a detailed monitoring of all the contributing brooks

to the main rivers (Grande, Porcón, Paccha and San Lucas) is elaborated. The discharge of the

brooks relevant for the río Grande are measured in June and July of 2007. So this discharges

are considered to be base flow values. The results are given in Figure 15, conform with Figure

7. This inventory covers 27 superficial waterbodies, in the río Grande and its contributors,

7 Conga is the extension gold- and copper mine project of Minera Yanacocha. It will be located 25km north-east of the current mining district, close to the city of Celendín.


49

rivers and brooks of which 67% had a discharge less than 5lps (Benavides Ferreyros et al.,

2007).

Figure 15 Measured discharges (in lps) of the brooks of the río Grande in June and July 2007 by INRENA for the

‘Inventario de Fuentes de Agua Superficial de la Cuenca del Mashcón’

In October 2014 the JURM visited the Dam on the río Grande. The main channels of some of

the commissions downstream did not receive any water because of very low discharges in the

river. In 2006 MYSRL and ALA-C settled the rule of a minimum discharge of 500lps from the

dam into the río Grande, to be regulated by MYSRL. The JURM measured themselves 288lps

(Table 15), downstream from the Atunmayo offtake. Both parties, the JURM and MYSRL,

agreed upon a better cooperation in the dry season of 2015 to avoid distrust.

Also questions were raised within the JURM about the actual discharge flowing in the offtake

of EPS Sedacaj S.A. (Figure 7; Number 4). Its license is 200lps but the drinking water demand

for the city Cajamarca increases every year. The environmental audit on EPS Sedacaj S.A. in


50

2011 remarked that the company does not have any registration of the volumetric flow that is

entering their offtakes, in the three rivers Grande, Porcón and Ronquillo. Their BT is only

equipped with a measuring rod so the discharge can be read at the moment itself (La Contraloría

General de la República, 2012).

Figure 16 JURM and representatives of their irrigation commissions visiting dam río Grande in October 2014

Table 16 Results parametric and non-parametric trend analysis on discharge measurements (elaborated by

COMOCA) in irrigation channel in the direct vicinity of MYSRL. 2-sided p-values are given with significance codes:

0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1. Increasing and decreasing trends are respectively indicated with (+) and

(-)

Irrigation Channel Measuring point Time series p-value Trend

analysis

Atunmayo CAM-1 2003-2014 (-) 0.034*

Carhuacero Yacushilla CCY-1 2001-2014 (-) 0.00017***

Cince las Vizcachas CCV-1 2004-2014 (-) 0.438

Encajón Collotan CEC-1 2001-2014 (+) 2.22e-16***

CEC-2 (+) 2.22e-16***

Quishuar CQ-1 2001-2014 (+) 1.192e-05 ***

CQ-2 (+) 0.00496*

San Salvador José de

Coremayo

CSC-1 2004-2014 (-) 0.00119***

San Martin Tupac

Amaru Río Colorado

CTU-1 2001-2014 (-) 1.500e-06***

CTU-2 (-) 0.036**

CTU-2A (-) 0.159

CTU3 (-) 0.230


51

Apart from the irrigation channels that have offtakes from the río Grande, an analysis is made

on the discharges in the channels, supplied by water from spring, that are located in the vicinity

of the mine. COMOCA measured on a monthly basis the discharges in one or more points of

these channels. A trend analysis is elaborated on the discharges of the channels in the catchment

of río Grande and the results are summarized in Table 16. Measurements started in 2001, 2003

or 2004. Increasing or decreasing trends are indicated and their significance with a p-value. The

locations of the measuring points are indicated on the map in Annex VII (Figure VIIA)

(COMOCA, 2006).

The different licenses over time, granted to the irrigation committee of SSJC, are collected and

can be used as an example of a proxy to see changes in the supply coming from natural springs

in the vicinity of the mine. It concerns a committee that covers 60ha irrigated land and in the

network an earthen main channel of 18km runs down from initially 7 water sources, most of

them close to the brook Corral Blanco; Figure 6 and Figure 7. In 1993 they received a license

of 55lps (ATDR Caj, 1993). According to Benavides Ferreyros et al., (2007) a new resolution

was written one year later, in august 1994 that consisted of a license of 40lps. In 2004 an extra

water right was granted to SSJC. It concerned a water usage permit of sources located on

MYSRL’s property, resulting in an extra discharge of 17.5lps (Benavides Ferreyros et al.,

2007). In 2010 the license of SSJC was defined by ALA-C, making use of 35 springs and a

resulting discharge of 41lps (ALA-C, 2010). This water right is still valid today (ALA-C, 2013).

In the same year a technical report was set up to characterize exactly the different water sources

that SSJC has a water right for. In the dry season of 2014, after a complaint of SSJC, the JURM

carried out an inspection with 2 measurements at different locations in the main channel that

resulted in discharges of 4.1 and 3.9lps (JURM, 2014).

4.2 Calibration of the CTF

The measured discharges and corresponding upstream heads are given in Table 17, as well as

the discharges calculated according to Manekar et al., (2007) (equation (2) and (3)) and

Temeepattanapongsa et al., (2013) (equation (1), (4) and (5)) in Table 18 and Graph 3. Free

flow is assumed, based on the design dimensions and calibration. But since the dimension

deviations of the constructed CTF there cannot be fully relied on the critical value defined by

the design; it can only be used as an indicator. Calculation of the ℎ𝑎

ℎ𝑏⁄ -ratio and a comparison


52

with the transition submergence, would give a more reliable calibration in situ. The two first

heights are definitely measured under free flow conditions. The last water height is a case of

doubt. The design of the flume included only a height up to 0.40m for free flow conditions;

Annex IV.

Table 17 Measured upstream heads (m) and discharges (m³.s¹־) for free flow calibration of the CTF in Tres

Molinos

Upstream head 𝒉𝒂 (m) Discharge Q (m3.s¹־)

0.155 0.056

0.320 0.177

0.415 0.331

Table 18 Characteristics of the trend lines, based on the measured height-discharge relations, and recalculated

discharges according to an excel power, the design, Manekar et al and Temeepattanapongsa et al equations.

Trend line Design Manekar et al. Temeepattanapongsa

et al.

Cd 1.445 1.499 1.454 1.243

n1 1.757 1.646 1.705 1.555

SSE 0.0009 0.0034 0.0010 0.0015

Q1 (m3.s¹־) 0.068 0.060 0.070 0.055

Q2 (m3.s¹־) 0.211 0.208 0.230 0.195

Q3 (m3.s¹־) 0.316 0.324 0.352 0.308


53

Graph 3 Graphical representation of the different trend lines. Black: Measured data points; orange: Excel power

relation trend line; grey: design equation; yellow: Temeepattanapongsa et al.; blue: Manekar et al.

4.3 Efficiency of the irrigation network

In Table 19 the discharge data (in lps) from 2 measuring tracks are given. The water loss over

the channel distance is represented in Graph 4. A division between concrete and earthen channel

is not made since not enough discharge data is available in the earthen channels. In Table 19

the earthen channel is indicated. An overall water loss of 5.7 lps.km¹־ can be derived. A

conveyance efficiency can be calculated depending on the distance the water has to travel over

the channel to reach a certain field. Some important observations made during the

measurements along the main, the Tres Molinos secondary and the El Triunfo tertiary channel,

can be remarked:

- In the first 200m the main channel runs through the garden of the hotel ‘Posada del

Purhuay’. At a certain point part of the water is captured and deduced to a pond from


54

the hotel. Via a tube underneath this little basin the water is returned to the main channel

and in theory it would function as a closed system (1 time observed).

- A lot of gates of tomas directas are not well closed or old and broken, and a small

proportion of the water mentioned for a certain parcel of a certain turn is spilled in some

of these preceding parcels (8 times observed).

- People use the water for other purposes e.g. washing their cloths and car. The water is

possibly partly returned to the channel, but it is highly possible that this practice creates

losses. In some cases people even block the stream with stones to have temporarily a

larger volume for washing (3 times observed).

- Illegal pumping up of water out of the main channel (1 time observed).

- Rocks in the main channel that blocks or slows the water flow down (3 times observed).

Table 19 Measured discharges (in lps) along the main channel and secondary channel of Tres Molinos, in function

of the distance of the bocatoma. * indicated measuring points are located on the secondary and tertiary channel

Distance

from BT (m)

67 743 1369 1872 2515 3450 3720* 3850* 4380* 5080*

10/09 84 75 71 70 66 66 59 57

12/09 87 69 71 71 63 51 56 56

Graph 4 Loss in discharge (lps) as a function of the distance (m) from the bocatoma running over the main,

secondary and tertiary channel of Tres Molinos


55

According to the of water losses over the channel, a mean conveyance efficiency (in %) can be

contributed to every soil type of TM characterized in Figure 10 and in 3.6.2.4. These efficiencies

are listed in Table 20 and will be used in the field water balance.

Table 20 Mean conveyance efficiency (%) per soil type in TM

Phaeozem Leptosol Vertisol Andosol

92 78 66 79


The resulting biomasses for the 3 irrigation scenarios (license, actual and crop requirement;

irrigation depths given in Table 10), and for the 4 different soil types present in TM (Andosol,

Leptosol, Phaeozem and Vertisol) are shown in Graph 5. The biomasses are expressed in dry

matter weight ton.ℎ𝑎−1. The irrigation depths that are used in these 3 scenarios per soil type

are indicated in Table 21. The applied depths in the case that water is not limited (crop

requirement) are the mean values over a time span of 14 years (2000-2013). WPb and WPirr

are calculated for all the scenarios and assembled in Fout! Verwijzingsbron niet gevonden.

and Graph 7. Both parameters are expressed in kg.m־ᶟ. A calculation of the TAW in the root

zone for the 4 different soil types, listed in Table 22, can help with the interpretation and

comparison of the performance of the different soils in TM. A important remark for the

interpretation of the results is that for the scenarios ‘Phaeozem Actual’, ‘Vertisol License’ and

‘Vertisol Actual’ respectively in 2, 2 and 4 years of the 14 the simulation resulted in a total

decease of the crop.

Table 21 Total irrigation depth (in mm) for the 4 soil types and 3 irrigation scenarios

Andosol Leptosol Phaeozem Vertisol

License 341 341 403 310

Actual 279 279 341 248

Crop requirement 568 ± 48 566 ± 48 505 ± 49 509 ± 49


56

Graph 5 Resulting biomass (ton DM ha¹־) of pasture growth in the dry season for 4 soil types and 3 irrigation

situations in Tres Molinos

Table 22 Profile and TAW characteristics of the 4 different soil types

Depth profile (m) TAW in profile (mm) Root zone (m) TAW in root zone (mm)

Andosol 0.45 29 0.45 29

Leptosol 1.00 36 0.60 36

Phaeozem 1.20 141 0.85 120

Vertisol 1.00 160 0.85 113

Graph 6 Biomass Water Productivity (kg.m־ᶟ) of pasture growth in the dry season for 4 soil types and 3

irrigation situations in Tres Molinos


57

Graph 7 Biomass Irrigation water Productivity (kg.m־ᶟ) of pasture growth in the dry season for 4 soil types and 3

irrigation situations in Tres Molinos


58

5 Discussion

5.1 Water availability in the Grande de Mashcón catchment

A baseline study of the natural hydrology of the Grande catchment does not exist, which makes

an evaluation of discharge changes in time more difficult. The collected data in Table 15 are

too scarce to draw conclusions. A possible scenario is that discharges strongly decreased in the

river during the first years of the exploitation and increased in the beginning of the 21th century,

after the initiation of the regulations of the different outlets of the mining district (Table 4 and

Figure 6), the request for a substantiated EIA and the minimum discharge agreement from the

dam río Grande. This reasoning is based on the statement of EPS Sedacaj S.A. that the lowest

discharge in the río Mashcón, of 20 years occurred in the same year as MYSRL started their

operations (Benavides Ferreyros et al., 2007). If 2002 is compared with 2013-2014, which are

the only long term monitoring events, this decrease in discharge is clear. This observation is

along the same line with the predictions that Stratus Consulting Inc., (2003) made, namely that

the average monthly discharge in the río Grande can increase up to 20% in the dry season. The

surprisingly low discharge measured by the JURM in 2014 is only a point measurement at one

specific moment. An institutional and technical support is necessary to confirm this observation,

and a continuation of discharge monitoring in 2015 and 2016 can result in a better evaluation.

The objectives that MYSRL mentions in their ‘water resource management’ in 2011 is to

“increase the discharge in the dry season for agriculture downstream, this through pumping

up, using, treating and discharging groundwater out of the open pits as well as through

collecting rainwater in the wet season to discharge it in the dry season”. Logically a natural

recharge of aquifers is inhibited first of all through pumping up of groundwater and secondly

by collecting rainwater and impeding it to infiltrate. This statement is reflected in the data as

well. The discharge monitoring of COMOCA shows, in almost all the channels, a decreasing

trend over the years. Encajón Collotan and Quishuar both receive treated water from the mining

operations, according to Table 4, and accordingly show increasing trends. According to the

inventory of INRENA in 2007, 94% of the 342 identified springs in the Grande catchment have

a discharge of less than 1lps, which makes their vulnerability even more pronounced.

An in-depth inventory of all the existing springs, type of usage, evolution in time, susceptibility,

quantity of users is necessary. An incentive is already given in ‘Inventario de Fuentes de Agua

Superficial de la Cuenca de Mashcón’ by INRENA in 2007. Continuation of the monitoring


59

project of RENAMA and ALA-C are also strongly encouraged. Both would improve the

evaluation of the hydrology response of the water management by MYSRL and agriculture in

the catchment. The monitoring and characterisation of the required conditions in small, and

seemingly less important, irrigation channels is especially necessary in view of the closing and

rehabilitation phase of the mine. Also similar monitoring events and inventories are

recommended in the catchments around the planned Conga mining district to have a proper

baseline over there.

5.2 Calibration of the CTF

The number of measurements for calibration of the CTF was low. A water height- discharge

relation could be defined and used within the operable range of the flume, so within the context

of the irrigation channel of TM in the dry season, and based on the characteristics of a CTF.

The actual flume differs from the designed dimensions, which results in a stronger contraction

and lower discharges for the same water height to be expected. This is observed in Graph 3;

which also shows all the different formulas. The design relation could not be used because of

the strong deviating convergence: length and divergence: length ratios, which are respectively

1:2 instead of 1:3 and 1:4.8 instead of 1:6. If an opportunity arises, extra measurements at more

water levels should be elaborated. A more accurate trend line can be established which fits the

measurements, and both the Manekar et al., (2007)- and Temeepattanapongsa et al., (2013)

trend lines approximated better. The Manekar-relation 𝑄 = 1.45ℎ𝑎1.7

is recommended to use,

taking into account a possible and maximum overestimation of the discharge of 15% within the

working range of 50-200lps. A safety limit of 115lps can be set as sufficient discharge according

to the license. Shortly downstream of the CTF a drop in the channel bed is present and therefore

extra calibration for submergence is not necessary. A measuring rod should be placed according

to the piezometric tap ℎ𝑎 in Figure 3. Before measuring, the CTF needs to be cleared of

obstacles, debris and eventually plant growth in order to obtain an optimal accuracy during

reading the rod.

5.3 Efficiency of the irrigation network

An overall water loss over the irrigation channel of 5.7 lps.km¹־ has been observed, although

there is a lot of scatter on the data which is due to strong local losses. A distinction between the


60

main channel in concrete and the secondary and tertiary earthen channels is not made. Losses

appear to be mainly caused by local losses like water robbery or ‘borrowed’ water for other

purposes, and old or not well closed gates. It would be even better to express water losses over

the amount of gates it has passed instead of over distance. The lined channels are in good

condition, and a 95% efficiency set by Brouwer et al., (1989) is acceptable. Although the

earthen channels of the secondary channel of Tres Molinos and the tertiary channel of El Triunfo

have not been checked for possible so called hotspots (Asghar et al., 2011), the soil in the valley

is observed to be rather robust, facing low seepage because of its clayey nature. On the other

hand vegetation growth in these channels is more problematic. It decelerates the flow and in

combination with turns in the middle of the day, high radiation, strong wind velocities, low

relative humidity and a very small slope, it can possibly lead to considerable evaporation losses

of a few percentage points. The Shilla secondary channel has not been evaluated on conveyance

efficiency, but it can be expected that seepage losses are more problematic here, regarding the

sandy soils and the poorly arranged channel structure, shown in Figure 17. Higher losses per

km and thus an efficiency lower than 78% is more realistic here.

Figure 17 structure of the Shilla secondary channel. 1st photo: black arrow indicates the channel

All these conveyance losses can regarded to improve distribution of water within the

commission, and not as entire water losses out of the commission, conform to Lankford, (2012).

Stolen water is still used and surplus water on the location of ‘Soil 4’ in Figure 10 will drain

directly to the parcels in the valley thanks to the steep slope and the solid bedrock on shallow

depth.


61

Small improvements are supposed to increase the efficiency up to a decent level. The problem

with the pond in the beginning of the main channel can save 10lps. An overall better supervision

on water robbery by the vigilante, correct closure of gates after the turn and replacement of old

gates in the main channel can recover 10-15lps. In the earthen channels a more frequent removal

of vegetation and debris can maintain the velocity. With these measurements estimated

efficiencies of 95% or more in the main channel and 75% in the secondary and tertiary channels

are feasible. The Shilla secondary channel needs a proper renovation to improve the

infrastructure and thus the conveyance efficiency. Also a more detailed distribution schedule

has to be elaborated to avoid tensions between farmers. In order to increase the application

efficiency, an evaluation and improvement of the distribution curve (Figure 4) of each parcel

has to be carried out.


The simulation in Aquacrop resulted in biomass, WPb, WPirr and irrigation depths for the crop

requirement scenario. The data is used to compare between different irrigation scenarios and

different soils within the commission. It is less feasible to use the absolute results from

Aquacrop e.g. of yield.

An important remark is that in all the simulations fertility is assumed to be optimal. However,

if no extra fertilizer is applied, except from the livestock manure, in a long term it can result in

fertility depletion. This factor can also induce biomass reductions.

The crop requirement scenario results in irrigation depths, needed to avoid any water stress.

Overall rainfall in the wet season of the observed timespan did not even fulfil the condition of

no water stress. For the dry season it resulted in a maximum achievable biomass for pasture,

i.e. 31.1 ton.ha¹־. Nevertheless, this value is not realistic in the current circumstances and can

only serve as an indicator because of two reasons. The actual irrigation supply has to be

doubled, and these volumes are not disposable. The crop requirement also assumes a higher

application frequency than once a week, which would imply a total revision of the irrigation

scheduling.

The most important factors playing a role in the biomass production are the TAW, the distance

from the BT, the CN-value, the saturated hydraulic conductivity (Ksat) and the thickness of the

soil. The distance from the BT basically determines the absolute irrigation depth at field level


62

since the water losses are assumed to increase over the channel distance, as elaborated in 4.3.

The TAW should play the main role since it expresses how many water a soil can store,

available for plant uptake. This parameter is the highest for the Phaeozem and Vertisol (Table

11-14). Together with the lowest conveyance losses, this results in the highest biomass

production for the Phaeozem, for both in the actual and license scenario. The Andosol and

Leptosol perform similar to the Vertisol, opposite to what is expected by the difference in TAW

and the strong draining character (Ksat) of the two first soils. The compensating factors are

probably the absolute irrigation depth, which is the lowest for the Vertisol, and the thickness of

the soils. The latter is due to the way how Aquacrop calculates water stress: If a soil is

characterized with a restrictive soil layer, Aquacrop perceives this as a closed reservoir. For the

same irrigation depth a more shallow soil is percentage-wise more filled than a profound soil.

Hence the roots in this shallow soil can more easily extract water, which is discussed in detail

by Van Gaelen, (2012). Both the Andosol and the Leptosol are characterized with a restrictive

layer at respectively 45 and 60 cm depth (Table 12 and Table 14). The depth of these reservoirs

is more than half the size smaller than the depth of the Vertisol (1.20m). In reality it is most

probable that the surplus water in both the Andosol and Leptosol would rather run down over

the bedrock. This is very likely partly because they are positioned on a slope (Figure 10) and

partly because of their strong draining character (Ksat in Table 12 and Table 14). Lower

biomass production than simulated, for both soils, can be expected under actual and license

circumstances. The dominant influence of the low water holding capacity of the Andosol and

Leptosol is also reflected in the higher irrigation depths needed for the maximum achievable

biomass.

The WPb of all scenarios are similar. The WPirr is more interesting for the irrigation

commission since irrigation water is scarce and thus this parameters reflects better the

performance relative to the input. The highest WPirr-values in the actual scenario for the

Andosol and Leptosol are logical. The more water is added to these soils the more can be lost

by the strong draining character (high Ksat) and the low TAW. For these soils smaller but more

irrigation applications in time are required. It can partly be resolved by e.g. installing a small

reservoir in the Shilla secondary channel, to store part of the water at their turn and irrigate

twice in the week. This is also feasible since homogeneity over the parcels can be maintained,

while irrigating only half the volume, due to the steep slope in the Shilla lateral. It is

recommended that the JURM, possibly within PSI Sierra, makes a characterisation of the water

supply, efficiencies and distribution in the Shilla secondary channel. The WPirr for the Vertisol


63

is also the highest for the actual application depth. Though it is more difficult to compare with

the other soils, because the Vertisol’s has a smaller net applied actual and license depth. Because

of its strong water holding capacity a small irrigation depth can be stored and used optimally.

There is no large change in productivity of the Phaeozem between the 3 scenarios, because the

3 irrigation depths are also more close to each other.

The Phaeozem is the most productive soil in the actual and license water supply scenarios

because of 3 reasons: it has the highest TAW in the root zone (Table 22), the profile is not so

deep as the Vertisol and the least losses occur over the channel before reaching its parcels.

Since maximum biomasses are also not achieved in the wet season it can be interesting to

investigate the performance and resulting quality for dairy products of other grass types, e.g.

kikuyu grass (Pennisetum clandestinum) proposed by Neal et al., (2011) because of its high

WUE, or other cultivars. This kikuyu grass is in Peru known as ‘grama’ and according to the

survey is it already present as 13% of the cultivated grass type.


64

6 Conclusion

Two objectives are achieved in this dissertation. Firstly an overview is made of water

distribution, and related changes, between mining industry and agriculture in the Grande de

Mashcón catchment. Secondly a detailed description and validation is performed in the Tres

Molinos irrigation commission of its water supply, efficiency and performance.

No baseline study of the hydrology (superficial water bodies, springs or aquifers) has been

elaborated before the establishment of the Yanacocha mine. The first years of the exploitation

a strong reduction in discharges in the río Grande were reported, but since the elaboration of

MYSRL’s more conscious water management, considering the water provision of commercial

agriculture downstream, the discharges in the río Grande were again increased. A problematic

issue are the springs, in the higher Sierra, nearby the mining district itself. MYSRL does not

take measures to maintain the natural recharge of aquifers. Irrigation channels supplied by

springs in the vicinity of the mine are significantly affected and deal with strong reduced flows.

An executive inventory and characterisation of these water sources does not yet exist and is

strongly recommended to local authorities or further research. The purpose, typical flow range

and vulnerability of these springs are the main elements that have to be registered. This

information could be related to existing documentation8 or further research in the hydrogeology

of the area. Two other academic focusses are recommended: the potential impact on the

hydrology of the expected Conga-project and of the closing phase of the Yanacocha mine.

An evaluation of the current water distribution between different offtakes on the río Grande is

interesting. This can easily and more frequently be carried out if more BTs make use of control

structures, like the calibrated cutthroat flume. In Tres Molinos a water supply according to the

license can increase biomass production with 15-17%, but overall the irrigation water is more

efficiently used when actual depths are applied. A pasture production without water stresses is

not even achievable in the wet season. A change to more efficient crops regarding water use is

thus useful to consider. Phaeozems are the most productive soils in the commission. The Shilla

lateral has less productive soils, poor maintained infrastructure and bad managed distribution

schedules. Considering improvements is necessary here. An overall water loss of 5.7 lps.kmˉ¹

is observed in the irrigation network. Water losses along the channel are mainly due to water

robbery, removal for other purposes and leakage through gates. In the earthen channels a more

8 E.g. Informe de Aguas Freáticas en el Emplazamiento by Lorax Environmental, (2004)


65

frequent and complete cleaning and removal of vegetation, debris and rocks in the channels can

improve the conveyance. In the overall network a better supervision by the vigilante on water

robbery and correct closure of gates after a turn is recommended. A total change of field

application or distribution mechanism is possible but two important remarks have to be taken

into account: the possible impact on the social structure of the commission and the cost of an

improvement, regarding both the increase in biomass as well as the irrigation productivity.

In Peru, decentralization of the power concerning managing water resources is still in progress.

More support is still necessary for water allocation, infrastructure and efficiencies in irrigation

commissions and in general defending agricultural values in the highlands of Peru. The program

of PSI Sierra is already a good incentive.


66

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72

8 Annexes

I. Cutthroat flume theory

Graph IA Graphical presentation of C1(free flow coefficient) and n1(free flow exponent) for the development of the head-discharge equation for free flow in a cutthroat flume (Skogerboe et al., 1973).

Graph IB Derivation of K1(the flume length coefficient) and n1(Free flow exponent) for the determination of the discharge under free flow circumstances in a cutthroat flume (Skogerboe et al., 1973)


73

Table IC Free flow calibrations for selected Cutthroat flumes (Values listed are discharges in cfs.) (Skogerboe et al., 1973)


74

II. Junta de Usuarios de Río Mashcón

Figure IIA18 Format orden of irrigation of the Junta de Usuarios de Río Mashcón

JUNTA DE USUARIOS RIO MASHCON

COMISION DE USUARIOS

SUB SECTOR HIDRAULICO TRES MOLINOS

ORDEN DE RIEGO

Nº_______

El usuario Sr.(a):_____________________________

Con ______ has de cultivo bajo riego

autorizadas_________, caudal _______ lts/seg.

Tiene orden para regar a partir del día _______

hora______ hasta el ______ a horas ______.

Horas totales de riego_______

Fecha: _____ de _______ del 2014

................................. ...............................

Entregué Conforme Recibí conforme

Firma del Delegado Firma del Usuario

Observaciones:

__________________________________________


75

III. Soil Classification Tres Molinos

Table IIIA Classification of Soils in Tres Molinos according to “Los suelos de la Cuenca del Rio Cajamarca (Estudio Semidetallado)” (Landa et al., 1978). The soil, discussed in ‘Geology and Pedology’ (3.1.2), are indicated

Denomination Origin Texture Drainage pH Slope

(%)

Depth

(cm)

Stoniness Erosion Potential use

𝒋𝟏𝑨𝒍 𝒑 𝒊 𝒍

𝟏 𝒊 𝟎 𝒏𝑰𝑰𝑰

Soil 1

gleyic Phaeozem alluvial heavy imperfect 5,5-

6,4

0-4 60-120 no impediment no risk arable land, suitable for intensive

cultivation and other uses

𝒅𝟏𝑻𝒖 𝒍 𝒂 𝒍

𝑰𝑰𝑰 𝒂 𝑰𝑰 𝒔𝑽𝑰𝑰𝒂

Soil 4

Lithosol or eutric

Regosol with

outcropping

rocks

volcanic

tuff stone

light excessive 5,5-

6,4

25 <30 sufficient stones to

impede required

works, fields can be

useful for forages or

pasture

severe marginal lands for agriculture (only

suitable for extensive grazing or

forestry)

𝒅𝟐

𝑻𝒖 𝒎 𝒆 𝒏

𝑰𝑰 𝒆 𝟎 𝒏𝑰𝑽

Soil 4

mollic Andosol,

eutric Regosol

volcanic

tuff stone

medium good 6,5-

7,4

13 30-60 no impediment no risk complexes of arable land,

suitable for intensive cultivation

with other generally non-arable,

suitable for permanent crops

(orchards, pastures and

forest)

𝒊𝑨𝒍 𝒑 𝑬 𝒍

𝟏 𝑰 𝟎 𝒏𝑰𝑽

chromic Vertisol alluvial Heavy good -

imperfect

5,5-

6,4

0-4 120 no impediment no risk complexes of arable land,

suitable for intensive cultivation

with other generally non-arable,

suitable for permanent crops

(orchards, pastures and

forest)

𝒋𝟏𝑨𝒍 𝒎 𝒊 𝒍

𝟏 𝑰 𝟎 𝒏𝑰𝑰𝑰

gleyic Phaeozem alluvial medium imperfect 5,5-

6,4

0-4 120 no impediment no risk arable land, suitable for intensive


𝒂𝟏𝑨𝒓 𝑳 𝑨 𝒍

𝟒 𝑨 𝟑 𝑺𝑽𝑰𝑰𝒄

Soil 2

Lithosol,

Cambisol or

haplic Phaeozem

sandstone

or

quartzite

light-

medium

excessive-

good

5,5-

6,4

26-50 30 machinery use is

impeded, fields can

only be used for

forages or pasture

moderat

e -

severe

marginal lands for agriculture (only


forestry)


76

𝒋𝟐𝑨𝒓 𝒍 𝒂 𝒍

𝟒 𝒊 𝟑 𝒔𝑽𝑰𝑰

Soil 2

luvic Phaeozem sandstone

or

quartzite

Light excessive 5,5-

6,4

26-50 60-120 machinery use is

impeded, fields can

only be used for

forages or pasture



forestry)

𝒂𝟑𝑫𝒐 𝒎 𝑨 𝑰

𝟑 𝒆 𝑰𝑰𝑰 𝒎𝑽𝑰

Soil 2

humic Cambisol

or haplic

Phaeozem

fluvioglaci

al or

aluvio

colluvial,

coarse

material

medium excessive-

good

6,4 13-25 30-60 sufficient stones to

impede required

works, fields can be


pasture

Moderat

e

complexes generally non-arable

lands, suitable

permanent crops with others, only

suitable for extensive grazing and

forestry

𝒊𝑫𝒊 𝒑 𝒐 𝒏

𝟏 𝒊 𝟎 𝒏𝑽𝑰

chromic Vertisol fluvioglaci

al or

aluvio

colluvial,

fine

material

Heavy bad 6,5-

7,4

0-4 60-120 no impediment no risk complexes generally non-arable

lands, suitable

permanent crops with others, only

suitable for extensive grazing and

forestry

𝑰𝑫𝒊 𝒑 𝑰 𝒏

𝟏 𝑰 𝟎 𝒏𝑰𝑰𝑰𝒄

Soil 3

soil association,

profound or very

profound depth,

basic parent

material, medium

to heavy textures

fluvioglaci

al or

aluvio

colluvial,

fine

material

Heavy imperfect-

bad

6,5-

7,4



𝒂𝟏

𝑨𝒓 𝒍 𝒂 𝒍

𝑰𝑽 𝑨 𝑰𝑰𝑰 𝒔𝑽𝑰𝑰

Lithosol,

Cambisol or

haplic Phaeozem

sandstone

or

quartzite

Light excessive 5,5-

6,4

5 30 sufficient stones to

impede required works

– machinery is

impeded, fields can be


pasture



forestry)

𝒋𝟏𝑫𝒊 𝒎 𝒍 𝒏

𝟏 𝑰 𝟎 𝒏𝑰𝑰𝒄

gleyic Phaeozem fluvioglaci

al or

aluvio

colluvial,

fine

material

medium imperfect-

bad

6,5-

7,4




77

IV. Design height-discharge relation CTF in Tres Molinos

Table IVA23 Water height- discharge relation under free flow conditions of the CTF in TM (Cotrina Fernández and Ramos Mejía, 2014)

Water height

𝒉𝒂(m)

Discharge

Q (lps)

Water height

𝒉𝒂(m)

Discharge

Q (lps)

0.01 1 0.21 115

0.02 2 0.22 124

0.03 5 0.23 133

0.04 7 0.24 143

0.05 11 0.25 153

0.06 15 0.26 163

0.07 19 0.27 174

0.08 23 0.28 184

0.09 28 0.29 195

0.10 34 0.30 207

0.11 40 0.31 218

0.12 46 0.32 230

0.13 52 0.33 242

0.14 59 0.34 254

0.15 66 0.35 266

0.16 73 0.36 279

0.17 81 0.37 292

0.18 89 0.38 305

0.19 97 0.39 318

0.20 106 0.40 332


78

V. Survey in Tres Molinos


79

Figure VA Survey for farmers in Commission of Tres Molinos for the field water balance, performed in October 2014.


80

VI. Simulation Strategy Field Water Balance in Aquacrop

The option ‘forage crops’ is not yet provided in Aquacrop 4.0 (Vanuytrecht et al., 2014). To overcome

this deficit a comparison is made to define the difference between the following possible simulation

strategies, for the period of 2000-2006 in the Leptosol:

- Crop rotation

- One crop cycle

The crop rotation represents 5 rotations of pasture within the dry season. In this case there is assumed

that pasture is planted again in every cycle. The mean frequency between two cutting events is based on

the survey and resulted to be 49 days. In the one crop cycle no interval cuttings are simulated and only

one harvest is carried out in the end of the growing season. Yield and response to water stress are the

main analysed parameters to evaluate both simulation strategies.

In Graph VIA the yield for both simulations in three-monthly interval is shown. Pasture under crop

rotation simulation has a larger standard deviation because every three months the crop starts to grow

from the germination stage. With water stress additionally the development of the roots and the canopy

expansion are subjected to water stress which determine the further development and the yield

production. The largest variation for both simulations are the two last periods; August- October and

October- December. Since this is the end of the dry season there is no water storage left in the root zone

so a retardation of rain events will give a greater drop in yield, and on the other hand a rain event which

takes place will have a relatively higher WUE and will result in an strong growth and yield increase.

Only in the first period (April-May) the yield is lower for the simulation of one crop cycle. This is logic

because the crop rotation reaches his maximal cover earlier and so develops earlier more yield.


81

Graph VIA Comparison yield in three-monthly interval for crop rotation simulation and one crop cycle simulation in Aquacrop, of pasture in Tres Molinos, Cajamarca

The distribution of the different consequences on the crop due to water stress for both simulations are

represented in Graph VIB and Graph VIC. It is clear that the absolute impact of water stress is larger for

the crop rotation simulation. Leaf expansion is the main consequence. So germination and crop

development are the most sensible stages, moreover because in this stages the roots develop as well.

Early senescence does not occur. For the one crop cycle simulation stomatal closure is the main issue

that lowers the yield. Like how was expected is stress on leaf expansion not relevant for the one crop

cycle simulation. Only one strong value in October- December of 2000 has an influence on the mean.


82

Graph VIB Water stress balance - Crop Rotation simulation

Graph VIC Water stress balance - One crop cycle simulation


83

VII. Monitoring COMOCA

Figure VIIA Monitoring stations COMOCA South (COMOCA, 2006)

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