FACULTY OF TECHNOLOGY
NAVID YARAGHI
ASSESSING THE IMPACTS OF ARTIFICIAL
GROUNDWATER RECHARGE STRUCTURES ON
RIVER FLOW REGIME IN ARID AND SEMI-ARID
REGIONS
Master’s Thesis
MSc Barent Environmental Engineering
Aug 2017
Supervisor:
D.Sc. (Tech.) Ali Torabi Haghighi
D.Sc. (Tech.) Anna-Kaisa Ronkanen
Contents
Contents ........................................................................................................................ 2
ACKNOWLEDGE ....................................................................................................... 5
1. Introduction .......................................................................................................... 6
2. Literature Review ................................................................................................. 9
2.1 Water scarcity in Iran ..................................................................................... 9
2.2 Groundwater Recharge ............................................................................... 10
2.3 Rainfall and Runoff modeling .................................................................... 12
2.4 Flood Routing .............................................................................................. 13
2.5 Seepage ........................................................................................................ 13
3. Case study ........................................................................................................... 15
4. Methodology ...................................................................................................... 20
4.1 Calculate natural flow (First Scenario) ........................................................ 24
4.2 Altered flow (second flow scenario) ............................................................ 27
4.3 Primary and secondary seepage analyses .................................................... 30
4.4 River analysis system .................................................................................. 32
5. Results and Discussion ....................................................................................... 34
5.1 Framework input .......................................................................................... 34
5.1.1 Natural and Altered flow ...................................................................... 34
5.1.2 Seepage rating curves ........................................................................... 35
5.1.3 River rating curve ................................................................................. 38
5.2 Downstream analysis ................................................................................... 39
5.3 Data uncertainty and feature of Mahrlou basin after AGWRS .................... 41
5.4 Framework Novelty ..................................................................................... 43
6. Summary and Conclusions ................................................................................. 45
References .................................................................................................................. 46
ABSTRACT
FOR THESIS University of Oulu Faculty of Technology
Degree Programme (Bachelor's Thesis, Master’s Thesis) Major Subject (Licentiate Thesis) Barents Environmental Engineering Environmental Engineering
Author Thesis Supervisor
Yaraghi, Navid TorabiHaghighi, Ali & Ronkanen, Anna-Kaisa
Title of Thesis
ASSESSING THE IMPACTS OF ARTIFICIAL GROUNDWATER RECHARGE STRUCTURES ON RIVER
FLOW REGIME IN ARID AND SEMI-ARID REGIONS
Major Subject Type of Thesis Submission Date Number of Pages Water and Environment Master’s Thesis August 2017 53.Pages
Abstract
In dry and semi-dry climate, Artificial Groundwater Recharge Structures are used for flood control and managed
aquifer recharge. These damps basin runoff response decrease the maximum flows and increase the runoff
duration through wet seasons. In this study, a framework to quantify the role of AGWRS in headwater tributaries
on the total water balance of major basin and alteration of flow pattern in the main river has been presented. The
study contains four main subroutines: rainfall-runoff model, reservoir flood routing, river analysis system and
seepage analysis. The flood hydrographs with different return periods are estimated based on the climatic data
and the characteristics of headwater basin. River flow analysis below the structure is carried out for two unsteady
flow scenarios, first with the hydrographs of the natural system (as pre-impact: quick flood with significant peak
flow) and second the altered flow hydrographs due to detention process in the reservoir (as post-impact: damped
flood lower peak with longer duration time). Two sets of dynamic water surface along the river (from the location
of detention structure (x=0) to the confluence point with the main river (x=L) are developed based on two
hydrologic conditions as results of river analysis system. The results of framework define the impact of flood
detention structure by comparing the timing, magnitude, and variability of flow. The Kamal Abad artificial
groundwater recharge in Mahrlou Lake basin in Southern Iran was selected as case study to demonstrate the
application of the created framework. Through the probability analysis, the return period for hydrological drought
have been compared in pre-impact and post-impact condition. The results clearly showed how embankments
influence floods in tributaries and in some cases the flow reduced significantly and disappear in tributaries.
Additional Information
ACKNOWLEDGE
Firstly, I would like to express my exclusive gratitude to my supervisor, Dr. Ali
Torabi, who has patiently clarified explanations on many questions I asked and
supported me while I’ve been entangled during the extremely important period of my
life.
Secondly, I am thankful of Dr. Anna-Kaisa Ronkanen because of all her succors,
financial supports and well-descriptive comments during my Master’ thesis period.
Thirdly, I would give all my expression toward my parents and my lovely brother,
Niam, who have supported me all the time with all the restraints and all I got could
not be attainable without their favorable permanence of giving love and attitude to
me.
At the end, I would love to thank all my friends in Iran who have believed and
encouraged me toward my way to reach this point especially my super lovely
brother, Shahin. Also without always-ready-to-give-company companions in Oulu
specially Maite Gurgue, I would not have been able to finish this work. My special
gratitude would be toward my explicit helpful brother, Ahmad who has shown me
the inspiration of loyalty, honesty and real friendship.
1. Introduction
Water is exclusively known as a crucial resource for future global development,
chiefly agricultural sector, would become as precious as oil in close future (Qadir et
al., 2003). In the coming decades, due to increasing global food demands, expanding
agricultural activities especially for countries in which their major business is based
on it, water scarcity would be the main issue for future human being life (Feike et al.,
2017). Consequently, not only agricultural production but also conclusively,
economic development would be negatively affected by irritating water scarcity
(UN-Water, 2016). This crisis would be intensified for arid and semi-arid regions
which are already suffering from water deficit (Mancosu et al., 2015). In arid and
semi-arid regions, more than 75% of available water is primarily consumed by
agriculture activities and related industries (Oweis, 2005; Biswas, 2007; Varis, 2007;
Nikouei and Ward, 2013). For instance, in Iran, more than 97% of water is being
used for agricultural purposes (Soltani and Saboohi, 2008).
In arid and semi-arid regions, climate condition would also harshly affect water
resources (Şen, 2015). Comparatively, in Iran, as a country which is mostly located
in the arid and semi-arid region, total annual precipitation, counted as the main
source of water, equals to 413 billion cubic meters. Totally, 25 billion cubic meter of
this water amount infiltrates to the aquifers and approximately 93 billion cubic
meters flow as the surface water. The rest 295 billion m3 of water would be
unattainable due to evapotranspiration etc. (Hojati and Boustani, 2010). As spatially
limitation in surface water in arid and semi-arid regions, the main part of water
demand is supplied by Groundwater (GW). In addition, due to changes in weather,
scarcity of surface water bodies and also simplicity in extraction, GW has been
considered as a reliable resource of water in Iran (Prathapar et al., 2015). Excessive
GW exploitation particularly in the agricultural sector and its mismanagement cause
a significant decrease in GW table in Iran(Zaidi et al., 2015).
Conducive to the recovery of declined GW table, many solutions are considered. One
of the main solutions is Artificial Groundwater Recharge Structure (AGWRS) that
aims to augment the GW table, which has been decreased mainly by the human
interventions, with transferring some parts of surface water to the aquifers close to
streams and rivers (Chenini and Ben Mammou, 2010; Torabi Haghighi et al., 2016).
Moreover, GW’s recharge confines streams during the period of low rainfall and
maintains it from replenishment (Xie, Cook and Simmons, 2016).
The function of AGWRS structure could be narrated by decreasing the peak of flow
and increasing runoff duration through wet seasons (due to flood routing in the
reservoir of AGWRS) and therefore, the flood has more potential for seeping to the
adjacent aquifer (Sakakibara et al., 2017). Through this function, depending on the
amount of GW recharged by runoff, downstream river’s flow regime would be
altered. The river regime alteration could exert several impacts on dependent
ecosystems (Torabi Haghighi and Klove, 2015) which will be the reason of
increasing the uncertainty of allocated flow for different purposes in downstream
(Torabi Haghighi and Klove, 2017), changing in the flood recurrence or even
disappearing (or shorten) downstream river part.
In this study, I present a multi-stage framework to quantify the impact of AGWRS
on the downstream river. I am going to show how much flow would be missed
through changing the shape of hydrograph due to the performance of AGWRS along
the river. The framework holds rainfall-runoff modeling, reservoir and river flood
routing and seepage analysis. In order to show the framework, the role of Kamal
Abad AGWRS in Maharlou lake basin in southern Iran (Fars Province) is selected as
a case study.
2. Literature Review
This literature review includes the comprehensive assessment of AGWRS’s impacts
on river flow regime in arid and semi-arid regions. Water scarcity issue has forced
researchers to find a solution to overcome the water deficiency and using GW has
been considered into their account Based on sustainable development principle, what
you use need to be refreshed and that is the reason here I would review the methods
of recharging GW. Using structures to store the water and make the chance for the
water to get seeped and release it to the downstream would be one of the ways to
fulfill the main goal of recharging GW and therefore, flood routing after the structure
would be essential to consider estimating the river regime behavior. How GW would
be recharged is based on the interaction of surface water and the soil characteristics
which the former brings up the rainfall-runoff discussion and the latter would be
bringing seepage topic into our discussion.
In order to discover the impacts of the structure the novel river engineering execution
has been developed in this study which is called river analysis system that would
clarify the behavior of the flow after passing the structure.
2.1 Water scarcity in Iran
Iran, as a country located in the middle east and due to its economic which comprises
agricultural sector, would have been faced several challenges in water sector which
are already growing gradually. Internal challenges which are considered also as
Middle eastern countries’ crisis would be addressed as following (Haddadin, 2002):
1. The imbalance in the population-water resources relationship
2. Lack of management in water resource sector
3. Social and economic development
The way all these challenges and even extra ones which have not been mentioned
could be solved would need progressive strives to avert a sure crisis. Following
suggestions which are mostly relied on agricultural policies shall be regarded as main
solutions which need precisely research and work on them (Kopsiaftisa et al., 2017).
- Protecting the existing water stock from degradation (Batlle-Aguilar, Xie and
Cook, 2015)
- Look for the training of all workers in the water sector and optimize your
number to reduce operating costs (Li et al., 2014)
- Increase the availability of water thanks to new innovations, i.e with
affordable techniques for the treatment and reuse of sewage; For water
harvesting; And for advanced management of soil moisture (Yang, Cai and
Mitsch, 2015).
- Increasing the pace of social and economic development (Ghayoumian et al.,
2007)
- Reconsideration in agricultural methods (Wösten et al., 2013)
- Reconsideration in national water strategies (Varis, 2007)
2.2 Groundwater Recharge
Among all water saving and conservation technologies for preserving water bodies,
herein I follow GW recharge concept which is counted as one of the most famous
methods to store and distribute surface water into the GW aquifers (Mancosu et al.,
2015). In order to avert GW table drop, replenishing and recharging GW artificially
would be selected as the main solution which has been agreed unanimously by
scientists, technocrats and planners (Samadder, Kumar and Gupta, 2011). Even
though AGWRS techniques have been used in the developed countries already for
several decades, in developing countries like Iran their use has recently occurred and
due to that, technics such as canal barriers, percolation tanks and trenches are under
experience (Samadder, Kumar and Gupta, 2011).
Selecting the best location for constructing the structure by implying all the
environmental impacts, surveying the basin, knowing the barriers and using
modelling software would have to be considered before any step which has to be
done by researchers precisely (Al Shakh and Sultani, 2002; Ghayoumian et al., 2007;
Chinnasamy et al., 2015; May et al., 2015; Sakakibara et al., 2017). In the last few
decades, there has been an enhancement of research and practice about the
restoration of rivers and their floodplain. The main reasons for this are the value of
river ecosystems as a habitat for conservation of species and habitats diversity,
recreation and aesthetics and flood protection. Moreover, Improve potential for
pollution and nutrient deposition has been considered as the reasons to be fulfilled
(Lehr et al., 2015).
In order to estimate the volume of seeped water, different methods have been used.
Based on the river: whether is it ephemeral or not, seepage meter or differential flow
gauging could be used. As long as the river is not ephemeral, the decay of GW
mounds, wetting fronts and the use of GW tracer would be performed (Batlle-
Aguilar, Xie and Cook, 2015).
2.3 Rainfall and Runoff modeling
The vast cost and use of labor met in the construction of a water resource project
requires great attention by designing specific Rainfall-Runoff models for its
successful performance (Chandwani et al., 2015). Conventional techniques demands
would be rainfall and runoff datasets which might be unavailable for basins in arid
and semi-arid areas in developing countries (Gumindoga et al., 2015). These models
are extremely dependent on the climate condition, physiographic and biotic
characteristics of the basin (Chandwani et al., 2015).
Having a reliable prediction of runoff magnitude from rainfall especially for un-
gauged basins would be difficult and time-consuming and moreover, it requires
considerable hydrological and meteorological data (Askar, 2013). Several methods
are in use and the SCS model is most commonly applied. Also, some other models
such as VIC, KINEROS, TOPMODEL, MIKE SHE an etc. has been used (Jiang et
al., 2015).
Because of flexibility and simplicity, the Soil Conservation Service (SCS) curve
number (CN) model is the most famous and widely used model to estimate runoff.
Besides estimating runoff for the small basins, the model has the capability of
establishing CN value for the different type of soil with different conditions (Ajmal
et al., 2015). Exclusively, the factors that are significantly affecting CN would be the
hydrologic soil group, vegetation cover type, land use, hydrologic condition and
antecedent runoff condition (USDA, 1986).
2.4 Flood Routing
In order to predict the temporal and spatial fluctuation of the flood, routing process
has been used in hydrology engineering (Soliman, 2010). Evaluating the effect of
storage on hydrograph shape would be obtained through practical execution which is
called Flood routing through the reservoir. The essential factors to enhance this
practical stage are inflow hydrograph, the relationship between reservoir spillway
water depth and detention storage and outflow hydrograph (Ward and W.Trimble,
1995). Ghosh (1986) have also worked with this method and improved continuity
equation of unsteady flow in reservoir and river as well.
2.5 Seepage
The issue that makes AGWR task possible is seepage. Seepage is a movement of
water in soils which either would be lost before reaching the aquifer or join the GW
from the surface water (Noorduijn et al., 2014). It would be principled by hydraulic
conductivity of the soil of the basin, channel geometry and boundary conditions
(Choudhary and Chahar, 2007). Soil hydraulic conductivity as a non-linear function
has been indispensable addressed as the most important transport property to control
the water movement through the soil layers (Li et al., 2014).
Moreover, the maximum seepage would be reached if the channel bed moves toward
a drainage layer which has the water table beneath its top surface and on the
contrary, seepage magnitude would be the least when the water table is close to the
water surface in the channel. Even though the main purpose of the AGWRS is to
facilitate the possibility for the water to get seeped, seepage of the water through the
river bed along the way would be counted as the main crisis for turning the river into
so called dead river which lose the water by seepage (Noorduijn et al., 2014).
3. Case study
Fars province as one of the thirty-one provinces of Iran is well-known as one of the
most important agricultural-polar with the major products including cereal, citrus
fruits, dates, sugar beets and cotton (Barthold, 1984). According to 300 mm mean
annual precipitation, Fars is placed in the arid and semi-arid region (Tavanpour and
Ghaemi, 2016). In these regions, a continuous drop in GW table has been faced
because of a dramatic increase in GW consumption due to agriculture growth and
economic development. Moreover, irrigation efficiency in Fars has been estimated to
be only 30 percent which is counted as one of the major reasons for the GW crisis
(Hojati and Boustani, 2010).
In the interest of recharging GW, more than 500 AGWRS have been built (or
planned to build) on tributaries of the river in Fras province (Soil&Water Subgroup,
2004). The AGWRS called Kamal Abad is one of those structures was selected to
comprehensively studied in this thesis. It“ locates in Sarvestan County, Fars
Province, Iran (28°50'24.42"N, 52°28'45.10"E) with the capability of storing roughly
260,000 m3. It has been built in the year 2008 (Fig. 1).
AGWRS was constructed on an ephemeral river on one of the sub-basins of
Maharlou lake basin, Maharlou Lake (also known as “Daryache-ye-Namak”, means
salt lake due to the high concentration of salt) is a shallow lake with maximum 600
km2 area which is located in the southeast of Shiraz (Jahanshahi and Zare, 2016).
The area of sub-basin is 31 km2 area with 3.88 hours concentration time and 13 km
river length that mainly cover by Gramineous vegetation and shrubs (Torabi
Haghighi et al., 2007). The distance of AGWRS to the confluence with the main
river in downstream is 3.63 km (Fig. 1). Fluvial Streambed armored with rock and
coarse gravel. Based on the field measurements the hydraulic conductivity equals to
15* 10-5
ms-1
. The Fluvial thickness is varied 50-200 meter.
Figure 1: Case study plan illustrating: location, Maharlou’s basin, Kamal Abad Sub-Basin and
streams.
Technically, the structure of Kamal Abad AGWRS contains a homogeneous
embankment (like earth dam with horizontal drain (filter) in downstream toe (to
control seepage and piping in body of structure) with maximum 10-meter height and
1200-meter length of crest with hydraulic conductivity of 7.5*10-4
m.s-1
for the
embankment material (Fig. 2a). The flow discharges to downstream through a
bottom outlet pipe with 40.00 cm diameter. The pipe is installed at 1.70 meters level
from AGWRS bed. The 55.70 m masonry step spillway is placed at 7.00 meter from
the bed of AGWRS to avoid overtopping flow from earth dam (Torabi Haghighi et
al., 2007).
Figure 2: Kamal Abad AGWRS’s technical information, a) layout and topography. b) The
hypsometric curve of the reservoir (area-volume-depth) c) cross-section and bottom outlet.
The relationship of height and area (Fig. 2b) has been obtaining from a topographic
map (Fig. 2a) and based on that the volumes for different elevations were calculated.
The active volume for GW recharge is 260,000 m3 corresponding to the level of
spillway which covers about 786,000 m2
area. However, with considering the height
of water on spillway through design flood, the maximum volume of the reservoir is
about 400,000 m3.
As the structure is constructed on the ephemeral river without any gauge to measure
the flow, to evaluate the inflow, the maximum daily rainfall on the studied area for
different return period (5, 10, 25, 50, 100 years) was estimated as 21, 25, 32, 36 and
40 mm respectively. This rainfall was calculated based on the maximum daily
rainfall in Sarvestan climatology station (the closest station to the study area) which
was provided by Fars regional water authority. Rainfall Intensity-Duration-
Frequency (IDF) was developed (Fig. 3a) based on the calculated maximum daily
data by using the experimental equations (Eq. 1&2), which is derived by
(Ghahreman and Abkhezr, 2004).
𝑃6010 = 1.34 × 𝑃24
0.694 (1)
𝑃𝑇𝑡 = (0.4524 + 0.247 𝑙𝑛(𝑇 − 0.6000))(0.3710 + 0.618𝑡0.4484)𝑃10
60 (2)
Where
P1060 = 1-hour precipitation with 10 years return period (mm)
t= duration of precipitation (h)
T= Return Period
P24 = Daily Average Precipitation (mm)
Figure 3: Rainfall-Runoff information: a) Rainfall Intensity-Duration-Frequency, b) Inflow
Hydrograph derived from SCS-CN method for 5 different return periods in the studied area.
4. Methodology
AGWRS functionality would be narrated as storing runoff water generated by
rainfall in its storage and giving the opportunity to the water to get infiltrated to the
soil which I call it primary seepage. By infiltration of the water, an aquifer which is
located on the embankment would be recharged artificially and simultaneously water
would pass the structure from the pipe provided below the structure to continue its
way to the downstream as an altered flow. Moreover, along the way water would be
seeped to the river bed which I call it secondary seepage. The main topic of this
study is to clarify how river flow would be altered before and after the construction
of structure.
To evaluate the impact of flow regime alteration first, I defined two sets of scenarios
for flow: natural and altered flow. In the absence of any flow observation in the
studied area, natural flows were calculated as hydrographs with different return
periods by using the synthetic unit hydrograph method provided by USCS (United
Stated Soil Conservation Service). The altered flow is the transformed shape of
natural hydrographs due to flood routing in the reservoir, storing and seeping into the
adjacent aquifer, indeed.
Two types of seepage reduce the magnitude of river flow below the AGWRS,
hereafter I call them primary and secondary seepage. The primary seepage occurs
through the reservoir seepage from bed and body of AGWRS which is considered as
the main function of structure to recharge the GW. The secondary seepage is the
seeping water along the river after releasing from AGWRS. To assess the impact of
AGWRS on the downstream river the combination of the results of different
engineering disciplines is needed which was designed as a multi-stage framework
(Fig. 4).
The designed framework contains following stages :
I. Quantify the natural flow (first set of flow scenario) for different return
periods.
II. Calculate the altered flow (second set of flow scenario) via the flood
routing in the reservoir.
III. Analysis the primary seepage to quantify the amount of recharged water
through the AGWRS performance. In this stage, a rating curve was
produced to show the magnitude of seepage during flood routing.
IV. Adjust the altered flow (from stage II) scenario by considering the result
of the primary seepage (from stage III)
V. The river flow analysis of downstream river to define the water level and
wetted perimeter along the river. In this stage, a rating curve was
produced to show the relation of the water height and discharge.
VI. Secondary seepage analysis and quantifying the infiltrated water along the
river. In this stage, a rating curve was produced to show the magnitude of
seeped water for specific water height.
VII. Figure out the tempo-spatial flow along the river for different flow
scenarios.
Figure 4: Multi-stage framework flow chart
The framework has several inputs and outputs (Fig. 4). In the first step (1&2&3),
with considering the basin geometry and rainfall, the natural flow will be defined (4).
The natural flow data is the input for the “Flood routing” and “Primary seepage
Analysis” execution function which is executing simultaneously (5&6). By using
steps (5&6), the altered flow scenarios would be defined (7). Two flow scenarios
(Natural and Altered flow) are the input for the functions (8&9&10).
Functions (8&9&10) are also running at the same time for different parts of the river.
The main part of the execution procedure which clarifies the distance which river
survive after the structure would be performed by these three stages of the modeling
(River Analysis & secondary seepage Analysis & Spatial flow Analysis).
The distance between releasing point of the structure to the point that river joins to
the next stream (from the outlet to downstream) would be considered as the main
part of surveying flow behavior along the way. The river has been divided into 10-
cm longitudinal elements to calculate the outflow from each element after secondary
seepage application.
The calculation would be starting for the first elements. For this element, inflow is
the outflow from the bottom outlet and then the outflow of the first element would be
the inflow for the next one. Based on the magnitude of flow and rating curve of the
river, the water level in current element of the river will be estimated. Regarding the
water level in this element and rating curve of secondary seepage, the magnitude of
seeped water will be obtained along the specific element. The seeped flow subtracts
from river flow and will be remarking as inflow for the next element.
The interaction between secondary seepage magnitude for different heights and river
rating curve has been conducted as the main stage to beget the novel loop with the
functionality of addressing seeped water magnitude and water level concurrently.
The sequence would continue until the difference between inflow and outflow of
each element reaches 1*10-3
m3s
-1 which mean no outflow could pass the next
element and would enlighten that the flow is disappeared on that certain point with
the certain scenario. This flow transferring to the next element will be continued until
all flow seeps along the river (river will be disappeared), or river joins to the lower
river. Through this multi-stage framework, the flow, water level and seeped flow at
different points in different time will be specified. Framework executes for natural
and altered flow to discover the response of river system along the river. The
comparison between scenarios could reveal the impact of AGWRS on the
downstream river. Technically, the framework has been developed in MATLAB
using several different inputs data. The inputs have been derived from SCS-CN
method and HEC-RAS & GEO-STUDIO software and inserted in MATLAB.
In furtherance of fulfilling the framework, four majors execute functions have been
applied and briefly explained below:
4.1 Calculate natural flow (First Scenario)
Considering the ungauged region in terms of flood hydrographs, Synthetic SCS-CN
method as the way of catering runoff has been chosen. The SCS has developed a
method of quantifying excess rain based on precipitation depth (P). A synthetic unit
hydrograph comprises all the characteristics of the unit hydrograph, except demand
of any precipitation and drainage data. It is originated from theory and experiment
and its purpose is to simulate the diffusion of the basin by estimating the lag of the
basin according to a particular formula or procedure (Fig. 5).
Figure 5: Synthetic Unit Hydrograph.
To define the natural flow, firstly runoff for each flood has to be calculated. Based on
the (Fig. 3a) which defined the IDF for each flood with different return periods,
rainfall had been calculated and would be considered into the equations below as P.
with the help of following equations runoff would be obtained.
𝑄 =(𝑃−𝐼𝑎)2
(𝑃−𝐼𝑎)+𝑆 (3)
𝐼𝑎 = 0.2 × 𝑆 (4)
𝑄 =(𝑃−0.2∗𝑆)2
(𝑃+0.8∗𝑆) (5)
𝑆 =2540
𝐶𝑁−10 (6)
0
0.2
0.4
0.6
0.8
1
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Q/Q
P
t/Tp
Where
Q = runoff (m)
P = rainfall (m)
S = potential maximum retention after runoff begins (m)
Ia = initial abstraction (m)
In order to estimate the CN for the river, hydrologic soil group, vegetation cover
type, treatment, hydrologic condition and antecedent runoff condition will be defined
from the charts. According to their infiltration rate, soils were categorized into 4
groups (A, B, C, D) which group A comprises sand, loamy sand or sandy loam and
group D comprises clay loam and silty clay loam. To obtain cover type mostly aerial
photographs and land use maps have been used. Treatment is a cover type modifier
which is meant to describe the management of cultivated agricultural lands. The final
factor which is hydrologic condition would indicate the effects of two last factors on
seepage and runoff (USDA, 1986). Based on all the information of the basin and
river, CN number 81 was selected for this study.
To obtain the natural flow hydrographs based on the mentioned method, Tp and Qp
(Fig. 5) have to be calculated by the following equations. Afterward, for each time
interval, by multiplying Qp to the magnitude of the horizontal vector of the synthetic
unit hydrograph, unit discharge will be attained.
𝑇𝑝 = 0.5 ∗ 𝑇𝑐 + 𝑇𝑙 (7)
𝑇𝑙 = 𝐿0.8 ∗(𝑆+1)0.7
1900∗𝑆𝑙0.5 (8)
𝑇𝑐 = 1.67 ∗ 𝑇𝑙 (9)
𝑄𝑝 =0.208∗𝐶𝑁
𝑇𝑝 (10)
Where
Tl= Time of Lag (Hour)
Tc= Time of concentration (Hour)
L= length(m)
S= potential maximum retention after runoff begins (m)
Sl= Slope of the basin (%)
Time of concentration is a conceptual value which is used to measure the basin’s
response to the precipitation event. It can be known as a time that water needs to
flow from the most remote point in a basin to the outlet. Thus, it depends on the
topography, geology and land use of the basin (Chow, Maidment and Mays, 1987).
4.2 Altered flow (second flow scenario)
Flood routing of the reservoir has based on level pool methodology which is defined
by Chow et al. (1987). As has been illustrated in the Fig. 6, the level pool
methodology would need given data on inflow hydrograph which is obtained from
natural flow hydrographs and also the volume-depth relationship of the reservoir
which is presented in the Fig. 2b.
As a first step for obtaining altered flow, based on the discharge-height relationship
of the reservoir, the relationship between Q (discharge) derived from the (Eq. 11) and
(𝑄 + 2𝑆/𝛥𝑡) (S=Storage) would be developed. The whole concept would be
narrated by (Eq.12) which shows that storage capacity is the difference of inflow
which is runoff calculated in section 4.1 and outflow which comes from (Eq. 11).
Development of (Eq. 13) based on (Eq. 12) for each time interval (j) has been done
and afterward, by using the Eq. 14, (𝑄 + 2𝑆/𝛥𝑡) would be computed and by the
obtained relationship gotten from last step discharge is produced. The procedure
would be continued for each sequence to the last time step.
Figure 6: Level pool methodology for flood routing of the reservoir.
𝑄 = 𝐶 ∗ (𝜋𝑑2
4) ∗ (2 ∗ 𝑔 ∗ ℎ)0.5 (11)
𝑑𝑆
𝑑𝑡= 𝐼(𝑡) − 𝑄(𝑡) (12)
∫ 𝑑𝑆𝑆𝑗+1
𝑆𝑗= ∫ 𝐼𝑑𝑡
(𝑗+1)∆𝑡
𝑗∆𝑡− ∫ 𝑄𝑑𝑡
(𝑗+1)∆𝑡
𝑗∆𝑡 (13)
𝑆𝑗+1−𝑆𝑗
∆𝑡=
𝐼𝑗+1+𝐼𝑗
2−
𝑄𝑗+1+𝑄𝑗
2 (14)
2𝑆𝑗+1
∆𝑡+ 𝑄𝑗 + 1 = 𝐼(𝑗 + 1) + 𝐼𝑗 +
2𝑆𝑗
∆𝑡− 𝑄 (15)
Where
C= coefficient which is considered typically 0.6
d= Outlet diameter (m)
h= Water elevation in reservoir (m)
I= inflow (m3.s
-1)
Q= Outflow (m3.s
-1)
S= storage (m3)
t= time (s)
j=interval factor
The outlet diameter of the structure (d) and water heights (h) and its related storage
(S) was counted as the main characters which are certainly derived from the structure
map (Fig. 2a) and has been mentioned in chapter 3. Moreover, apart from outlet
water magnitude, seeped water has been measured (primary seepage) and detracted
as well to define the outflow from the structure. Compare to original flow; altered
flow has smaller peak discharge and longer runoff duration.
4.3 Primary and secondary seepage analyses
As the main purpose of the AGWRS is fulfilled by the seepage phenomena,
obtaining the magnitude of the water loss into the aquifer would be the main goal of
this stage which is being illustrated by the rating curves. Primary and secondary
seepage rating curves would represent the discharge of the seeped water into the
aquifer based on the water height in the reservoir or along the river way. Seepage
discharge is the function of water height and on top of that water, height is the
function of time and inflow (GEO-SLOPE International Ltd., 2013).
𝑄𝑠𝑒𝑒𝑝 = 𝑓(𝐻) (16)
𝐻 = 𝑓(𝑡, 𝑖𝑛𝑓𝑙𝑜𝑤) (17)
Maximum under covered area by water in the reservoir would be incumbent to fulfill
the mentioned target which has calculated by using topographic maps of the
AGWRS.
In pursuance of acquiring water loss in reservoirs, Geo Studio 2007 software has
been applied to model water behavior and the water infiltration pathways. GeoStudio
allows to combine analysis using different products in a single project modeling,
resulting from one point to another. Moreover, GeoStudio gives powerful
visualization tools, including graphs, contour maps, isolines, animations, interactive
data retrieval and exporting data into tables for further analysis.
Going through Geo Studio SEEP/W analysis, initial priorities are to allocate
geometry characteristics, material properties, and boundary conditions. Material
properties such as water content and hydraulic conductivity (K) would be obtained
by soil experiments which had done in soil mechanical laboratory (Torabi Haghighi
et al., 2007). Boundary condition which has been applied to the upstream face of the
structure is a dynamic boundary, fluctuating by time, and it is obtained from previous
step (flood routing). The downstream face would be marked by zero-flux boundary
condition and the outlet pipe, which has been passing water, would have been
recognized by zero pressure zone supposing to make seeped flow. The software
output would present discharge of seeped water for 1 m length of reach which has to
be multiplied by the length of the wetted area.
The relation between seeped water discharge and elevation of the reservoir was
implemented in the equation of flood routing which has been designed to adjust the
outflow. Implementation needs water height-area relation as well as water height-
length relation to define the Height-Discharge relation for 1-meter wide of the reach.
Seepage analysis for river bed (Secondary seepage) has been done by Geo-Studio to
quantify the seepage discharge along the river while flow with different heights
would pass. Seepage discharge would be the function of flow height and hydraulic
conductivity which might differ spatially and temporally. Potential seepage face has
been selected as a boundary condition of the river cross section due to indicating that
no additional stream would be added or removed at those certain points.
The secondary seepage depends on the flow scenarios. Through the altered flow
scenarios due to routing process (Fig. 7), the longer runoff duration and the lesser
peak of flow could lead to increase the opportunity of seeping water into the aquifer.
The magnitude of primary and secondary seepages is also contingent on geotechnical
features of the embankment and downstream bed river substances. Hydraulic
conductivity and river morphology would most certainly have an influence on seeped
water discharge (secondary seepage).
To simplified the framework execution, the seepage was modeled based on the
steady state, while here I am facing with variation in upstream boundary condition,
and different soil moistures (dry, semi-saturated and saturated).
4.4 River analysis system
Discovering the discharge of flow by knowing water level in the river could be
attained by having rating curve of the specific cross section which is extracted from
topographic plans of the study area. In order to obtain the rating curve of river, the
Manning equation has been used.
𝑄 =𝐴
𝑛∗ 𝑅
2
3 ∗ 𝑆1/2 (18)
𝑛 = (𝑑50
16
21.1) (19)
Where
Q= Discharge which varied from 0.5 to 20 m3.s
-1 in my study
R= (A/P) The hydraulic radius (m)
A= Area (m2)
P= wetted perimeter (m)
S= The slope of the hydraulic grade line or the linear hydraulic head loss (L/L) which
is considered 0.008 based on the topography map
n= Manning number which is considered 0.038 based on the equation (19) which is
presented by (Chow, Maidment and Mays, 1987)
d50 = mean particle size (m) which calculates base on field measurement (Torabi
Haghighi et al., 2007)
Defining the rating curve of the river was done by HEC-RAS software Version 5.0.3.
This software allows the user to perform a constant flow dimension, one and two-
dimensional unstable flow calculations etc. Regarding executing the last function,
discovering the water height with specific discharge, to get the discharge of seeped
water along the river would be fulfilled by HEC-RAS. The output of this stage would
be essential to calculate BC for secondary seepage analysis.
5. Results and Discussion
According to this study, each step’s results are summarized and discussed as the
following.
5.1 Framework input
As has been narrated in methodology steps, altered flow and seepage results together
with river rating curve would craft as an outstanding combination to fulfill the main
target of this study.
5.1.1 Natural and Altered flow
Natural flow hydrographs which has been extracted from SCS-CN method by using
different rainfall (obtained from the modified IDF curves (Fig. 3a)), has been
illustrated in Fig. 3b. The hydrographs with 5, 10, 20, 50 and 100-year return period
has been applied in flood routing process to obtain altered flow hydrographs (Fig. 7).
The peak of natural flows with 5 return periods have been calculated as 1.71, 3.80,
7.28, 10.37 and 13.79 m3s
-1 and due to AGWRS performance have been reduced to
0.64, 0.91, 1.15, 1.37 and 1.57 respectively. Furthermore, the base time for inflow
and outflow would be 20 and 85 hours for natural and altered flows respectively (e.g.
for 100 years period demonstrate in (Fig. 7).
Figure 7: Natural and altered flow with 100 years return period
5.1.2 Seepage rating curves
To estimate the magnitude of seeped water through the performance of AGWRS the
seepage analysis behind the AGWRS (primary seepage) and along the river has been
done by using Geo studio. Based on the primary seepage analysis, the volume of
seeped flow to aquifer for the central cross section of AGWRS during flood routing
was 75.8, 118, 171.8, 208.2, 242.7 m3 for 5, 20, 10, 100 years return period
respectively. Considering the topography of the site, by approaching to the left and
right abutments the height of the embankment is reduced and so, the rate of seeped
flow would be decreased. Based on the topography of the Kamal Abad site (Fig. 2a)
the flow discharge from body and bottom of AGWRS for different depth of water
have been calculated and demonstrated as rating curve for AGWRS (Fig. 8a).
For the secondary seepage, according to different discharge the wetted perimeter and
depth of flow has a dynamic temporal pattern, thus the seeped flow for wetted
0
2
4
6
8
10
12
14
16
0 10 20 30 40 50 60 70
Dis
char
ge
(m3s-1
)
Time (Hour)
____Natural flow
……Altered flow
perimeter was analysed (Fig. 8b). The executed boundary condition for secondary
seepage analysis is the river water level which extracted from rating curve (Fig. 10).
By using the river rating curve for different flows, the depth of water in river was
estimated, and consider as BC for secondary seepage model, the magnitude of
seepage in different depth of water was calculated and represented as seepage rating
curve for the river (Fig. 8b). Based on the seepage analysis the seeped flow for
different flood return period for natural and altered flow is deferent, for example
during 100-year return period flood the seeped flow for the 1-meter width (when the
maximum flow is running in the river) of the cross section of flow during natural and
altered flow are 4*10-3
and 81*10-5
m3s
-1.
Even though during altered flow the maximum river flow is less than natural flow,
the magnitude of seepage is increasing due to increment the time for seeping in
altered flow scenario (85 hours) which is longer than natural scenario (20 hours).
Although in both primary and secondary seepage analysis, the water level is
fluctuating, to simplify the process in the framework, developing seepage rating
curve has been done under steady-state condition. This simplification action would
not affect the result of the study which is showing the impacts of the structure on
river flow. By neglecting the simplification action, the river would have been
disappeared earlier which would be an evidence for the study’s claim on the negative
impact of structure on the empirical river, indeed.
From both graphs discharge of seeped water in different heights could be extracted.
(Fig 8.a) is illustrating that the increase in the area of the under-covered region by
raising the water level in the reservoir would make the graph logarithmic. On the
other hand, in river analysis, due to an avertable increase of wet area by boosting
water level, the graph would be depicted as linear.
Figure 8. a) Seepage Rating curve for the reservoir which is increasing logarithmically. b) Seepage
rating curve for river bed material which is increasing linearly
The output of the software which is illustrating the seeped-water discharge for 1-
meter wide of the length would be observed in (Fig.9). Also contours and flow
Figure 6: GEO STUDIO Software output. a) Primary seepage related to the structure, b) Secondary
Seepage for the river cross section
directions would be observed which is shown in different colors.
5.1.3 River rating curve
HEC-RAS has been used to obtain rating curve for our particular case study with
defined river’s characteristics. Ten cross sections with average 60 meters width along
the way of the shallow river with 2 meters height have been adjusted in software and
with considering Manning number equals to 0.038 rating curve for the river has been
conducted (Fig. 10b). As has been explained before, the output would give the
specific height for certain discharge value to the extent of extracting seeped water
discharge from secondary seepage rating curve (Fig. 9b). The loop which has been
discussed has been playing its role by applying for execution order in conjugation
with these two graphs.
Figure 7. a) HEC-RAS output for various magnitude of discharge. B) Downstream River Rating
curve.
5.2 Downstream analysis
In natural flow scenario, all flood with more than five years returns period could join
the downstream river. The natural flow coming from the flood with five years return
period after running about 2952 m would be disappeared (all flow seeped to aquifer).
Before construction of AGWRS the floods with return period more than five years
have contributed to downstream part of the river but after the construction, the
contribution is missed and river condition from the ephemeral river has changed to
the dry river and it would be addressed as some sort of desertification process in this
region. Downstream river previously receives water each ten years, but this
AGWRS changes it to more than 100 years return period.
Spatial flow analysis below the AGWRS is carried out for two flow scenarios, first
with the natural hydrographs of the system (as pre-impact: quick flood with
significant peak flow) and second the altered hydrographs due to detention process in
the reservoir (as post-impact: damped flood lower peak with longer duration time
(Fig. 7).Two sets of dynamic water surface along the river (from the location of
AGWRS (x=0) to the confluence point with the main river (x=L) are developed
based on two flow scenarios as results of river analysis system and seepage function.
Prior to the construction of AGWRS, natural flood with ten years return period
would have been meeting the downstream river but after the construction, even flood
impacted by AGWRS with 100 years return period could not reach to the
downstream river and would be disappeared after 2890 meters below the releasing
point. In Table.1 length of the flow which could be run after passing the structure
before getting dry because of water infiltration along the way has been illustrated for
each return period.
Table 1: Length of the downstream river calculated based on pre-impact and post-impact of the
AGWRS
Return Period Before (m) After (m)
100 5525 2890
50 5019 2800
25 4480 2695
10 3668 2564
5 2952 2404
5.3 Data uncertainty and feature of Mahrlou basin after AGWRS
Sources of uncertainties in current studies would be begotten by (i) observed data
(ii) rainfall-runoff modeling component (iii) Soil properties and seepage analysis and
(iv) river analysis components.
Along the way of rainfall-runoff modeling with (SCS-CN) method, CN number
would have a considerable impression on inflow hydrograph that needs to be selected
delicately (Ajmal et al., 2015). Case study basin is located in poorly consolidated
alluvial-colluvial deposits in young terraces which are consisting of sub-rounded
gravels and sand, silt and clay (Geological survey and mineral exploration of Iran).
Based on the exported information, the soil could be set in Group A which has low
runoff potential and high infiltration rate along with high rate of water transmission.
Cover type of studied region could be known as fallow with the good hydrologic
condition and according to TR-55 (Urban Hydrology for Small Basins), CN number
assumed 81.
Hydraulic conductivity of saturated soil has been selected based on field sampling
from reservoir and river bed materials. There are many limitations for geotechnical
tests, depends on the size of the project the number of tests would be different. The
selected soil permeability was agreed with the range of soil properties in the
available standard. For instance by considering Swiss Standard SN 670 010b which
has been referenced by (Gashti, Malaska and Kujala, 2014; Yiediboe et al., 2015),
the river bed soil classified as poorly graded gravel, sandy gravel, with little or no
fines (similar with observed condition in Kamal Abad) the permeability of soil could
be varied between 5*10-4
and 5*10-2
m.s-1
that for our study was 2*10-4
m.s-1
for
river bed and 75*10-5
m.s-1
for the reservoir embankment.
Beyond of all uncertainties about seepage and soil conditions, the main idea of this
work is showing the impact of AGWRS on the river regime, considering the
unsteady condition for seepage in dry condition of the soil causes more seepage and
the river would disappear in less distance than what I mention in session 5.2.
The results also show the structure is over designed, as the storage capacity of our
case study is about 260,000 m3
while the volume of the flood with 100 years return
period which is counted as a rare phenomenon would carry 143,000 m3 water.
According to this extra volume in the reservoir, I could expect not only for flood
with return period 100 year the following river disappeared before joining
downstream river but also for even bigger floods or forever this river would have
eliminated from Maharlou lake system.
In arid and semi-arid regions, due to water over demand, water bodies especially
lakes have been getting jeopardized (Najafi and Vatanfada, 2011; Torabi Haghighi
and Klöve, 2017). Even though survival of studied sub-tributaries would be
neglected because of not having an impressive impression on Maharlou’s Lake basin,
impacts of losing it as one of the lake’s resource would be recommended to consider
into account. Constructing bunch of similar structures surrounded on Maharlou’s
basin shall be counted as one of the reasons leading to declining in water levels in the
mentioned lake.
5.4 Framework Novelty
Even though, each step of this multi-stage framework which has been surveyed, had
been studied before, but the combination of this package would regard as novel
overview on this mismanagement of over design of AGWRS. In posterior research
on finding the appropriate location for flood detentions and GW rechargers which
has based on either geophysics and hydraulic parameters (Abdi, 2000)or hydrologic
soil group characteristics (Zehtabian and Zormand, 2009) or using GIS tools (Al
Shakh and Sultani, 2002) or etc., considering the downstream river survival has been
neglected. By applying the briefed framework, the appropriate location could be
improved.
Even though, each function had been studied particularly, a combination of these
functions would present a novel survey aiming to assess the AGWRS’s concerns.
Here I show how a small structure could remove the contribution of some part of the
basin and moreover, present a framework to evaluate the impact of small hydraulic
structure on the basin has been made.
It would be recommended for future research based on the briefed framework which
I have been making through this study to make the survey for different climate
conditions and different soil properties to make a general guideline for evaluation the
impacts of the structure. Also applying the framework on several tributaries of a
bigger basin to observe the whole impact of each structure on the main river could be
done as a future research plan. Discussing about economic costs of the missing of
each tributary and moreover, total cost on the bigger projects like dam, made on the
main river, would be amusing topic to go for having research.
6. Summary and Conclusions
The study has encompassed multi-stage framework which represents novelty view to
improving GW recharge methods. Quantifying the impact of AGWRS on natural
flow has been done and routed flow has been derived in direction of evaluating both
flows’ regime along the way of the river. Considering the amount of seeped water of
the tributary along the way and before the structure both by implementing seepage
analysis shall be regarded as main execution when the structure is being under the
process of finding an appropriate location to be constructed.
Even though, recharging GW is inevitable, chiefly for arid and semi-arid regions
which GW counts as a most reliable source of water for the agricultural sector,
ruminating on the structure’s impact on the downstream river and consequently on
the bigger ecosystem recommended to be presumed. The negative impact of the
structure on the downstream river by making the river dry before reaching the main
tributary would be counted as the main result . Making a river dry would defiantly
have irrecoverable costs which are well-descriptive by the researchers.
In a nutshell, constructing small structures on small tributaries without recognizing
damages on downstream would cause bigger problems on main rivers due to
accounting on the water which is gained from each tributary.
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