Application of Invest`s Sedimentation Retention model for restoration benefits forecast at

Cantareira Water Supply System

Introduction

Healthy forests regulate water flows, protect watercourses and maintain water quality by

reducing sediment and filtering pollutants. The population that live in main Brazilian urban

centers depend on major watersheds, such as the Piracicaba-Capivari-Jundiaí (PCJ), which

headwaters feed the Cantareira Water Supply System, that provides water to 50 percent of

São Paulo Metropolitan Area population (9 million people). Loss of the forest has contributed

to soil erosion, polluted waterways, change in seasonal water flow, and a decline in water

quality. Restoration and protection of ecosystems located at these strategical watersheds for

water supply can provide a significant increase of ecosystem services that millions of people

rely upon to meet their basic water needs.

The Water Producer Program (WPP), an original concept developed by the Brazilian Water

Agency (Agência Nacional de Águas – ANA) in 2004 and supported by The Nature Conservancy

at its very beginning, is now the Brazilian constituent of Latin American Water Funds

Partnership, a bold initiative launched by The Nature Conservancy, FEMSA Foundation, Inter-

American Development Bank (IDB), and Global Environment Facility (GEF). A Water Fund is an

innovative way to collect money in recognizing of nature´s services and reinvest that money in

conservation. Since a healthy watershed minimizes water treatment costs, the funds attract

voluntary contributions from large water users downstream, like water utilities, hydroelectric

companies, or industries. Revenue from these investments is directed to recover or preserve

key lands upstream that filter and regulate the water supply, as well as to create incentives for

sustainable economic opportunities that have a positive impact on local communities.

WPP is providing financial compensation to farmers living in critical water production areas in

return for reforestation of degraded areas and protection of existing forests on their

properties, and soil conservation practices as well. The program is based on the notion that the

people who benefit from a service, such as clean water, should compensate the provider of

that service. This financial compensation can come from water user fees, government

programs and voluntary payments. The first Water Producer project, in Extrema municipality,

started in 2006 and it was the first public Payment for Ecosystem Services project in Brazil.

The Water Producer program is applying modeling tools that can provide a technical basis for

supporting the decision-making on the best alternatives for land use management in a basin,

towards to ameliorate or preserve hydrological ecosystems services offer, such as “natural

filtration” of sediments and nutrients. One of these tools is the model package INVEST

(Integrated Valuation of Ecosystem Services and Tradeoffs), the ecosystem services modeling

initiative from Natural Capital Project (supported by Stanford University, The Nature

Conservancy and WWF).

The Natural Capital Project developed the Invest package to map ecosystem services and

quantify the value of natural capital in a clear, practical and reliable way, demonstrating the

potential return that comes from investment in nature conservation and restoration.

Study Area

The Cantareira Water Supply System, located at the northeast of São Paulo’s Metropolitan

Region, is a complex of 5 headwater watersheds (4 of them being part of Piracicaba basin) that

are interconnected by tunnels that promote the water transposition of 33 cubic meters per

second for Upper Tietê basin, where it will be treated and delivered for 9 million inhabitants of

the biggest metropolis in South America.

The total area of watersheds asset is 227.950 hectares (551.640 acres), of which little more

than 24 % was covered by natural vegetation in 2010 (ISA, 2012); despite the fact that

deforestation rates have significantly decreased in this region in the last 20 years, water

quality has being affected by former forest conversion and present agricultural and grazing use

in hydrological sensitive areas as riparian areas and steep slopes.

Stream buffers, slopes steeper than 45º, and hill tops, that are defined by Brazilian Forest Code

as “Permanent Protection Areas” (APP in portuguese), cover an area of 36.844 ha of Cantareira

System; by law these areas should keep its natural vegetation. However, a land use assessment

(ISA, 2012) showed a very concerning scenario: only 30% (11.067 ha) of these areas were

effectively preserved, while 70% (25.777 ha) of them were deforested and were used for

economical activities, as grazing, in its majority.

Since 2006, The Nature Conservancy acts on Cantareira System through Water Producer

Program, by supporting ecological restoration activities associated with implementation of

Payment for Ecosystem Services schemes that also includes the financial support for other

activities as natural remnants conservation and soil conservation practices. Until now, about

200 hectares of degraded areas have being restored to its original cover (forests, wetlands and

grasslands) and more than 1.000 hectares of natural remnants are protected by PES contratcs,

signed with more than 125 landowners. By leveraging investments in restoration, TNC expects

to significantly change the landscape and improve ecosystem services offer at this strategic

water supply system.

Map 1 – Cantareira Water Supply System, showing also São Paulo Metropolitan Region

Map 2 – Land Use at Cantareira Water Supply System in 2010

Methods

For Cantareira Water Supply System, we have applied Invest`s Sedimentation Retention model

to estimate the reduction of sediment production that could be brought by restoration and

conservation actions in the most susceptible to erosion areas. There is a scientific consensus

that natural vegetation can act as a sediment trap, by catching the soil particles carried by

upslope runoff. The Sedimentation Retention model allows the simulation of erosion and

sedimentation dynamics at different scenarios of land use, which can be built using GIS tools,

in order to allow a comparative analysis of sedimentation abatement considering different

land use scenarios, related to different management approaches and interventions intensities,

in the same area of study. With this exercise we are trying to have a prognosis about how

much of sediment export that could be avoided by the restoration activities planned for the

Cantareira Water Supply System. Another major outcome from Sediment Retention model

application is the identification of most sensitive (in terms of sediment production) inside this

region, what can allow us to concentrate our restoration efforts at these areas, since we hope

that benefits in terms of sediment reduction would be proportionally bigger if we prioritize the

intervention at these very places.

As a baseline scenario we used the best available land use map of this region, developed by

Instituto Socioambiental, in 2012 (ISA, 2012), that reflects the land use condition in 2010.

We simulated the ecological restoration of these areas by developing an hypothetic land use

maps that represents 2010 land use scenario with restoration of most fragile (greatest

potential sediment production) degraded parcels. For the elaboration of this Land Use

Intervention Map, we first ran Invest’s sediment retention model using the “current” land use

situation, i.e. the 2010 land use map of Cantareira System. Then, we have analyzed the output

raster of sediment export rate by pixel (s_export output file) and we have selected all pixels

that showed a potential sediment production bigger than 0.28 ton/pixel (7 ton/ha, since pixel

area is 400 sq mts); then, after using a majority filter for pixel clumping and having selected

only patches inside pasture, bare soil, mining or agriculture land uses, we replaced these

patches in the original land use map with pixels considering forest cover (hypothetical

restoration) parameters, or agriculture with soil conservation practices parameters, according

to former land use (forest restoration in pasture, mining or bare soil and soil conservation in

agricultural areas).

The sedimentation modeling processing was done considering 2 land use scenarios: 1) 2010

land use and 2) 2010 land use considering restoration or soil conservation of most fragile

degraded areas.

Results

According to the screening criteria related above, we have been able to identify land patches

with higher sediment delivery potential (higher than 7 ton/ha/yr), that sum 9.815,7 ha, as is

shown in the table below. As we can see in the table, most of these fragile areas are occupied

by grazing activities, which can increase the risk of erosion at these areas due to cattle

movement.

Table 1 – Land Use at areas identified as priority for interventions in Cantareira Water Supply

System

Cantareira Water Supply System (Total Area 227,893.0 hectares)

Eligible Land Use for interventions

Priority Areas (ha) Land Use Post interventions

% of total area

Pasture 9.314,5 Forest 4,09%

Agriculture 255,6 Agriculture with Soil Conservation

0,11%

Bare Soil 165,3 Forest 0,07%

Mining 80,3 Forest 0,04%

TOTAL 9.815,7 4,31%

After running these “before and after” land use scenarios we achieve the following estimated

results:

- The current erosion rate (USLE) for Cantareira System was estimated in 18.1

ton/ha/year, and the calculated sediment delivery was 2.6 ton/ha/year, indicating a

sediment delivery rate of 14.4%.

- Considering the restoration or soil conservation of the most potentially sediment

producing areas (equivalent to 9.8 thousand hectares, or 4,3% of total area), we

estimated an erosion rate (USLE) of 15.7 ton/ha/year, and a sediment exportation of

1.2 ton/ha/year, which corresponds to a sediment delivery rate of 7.9%.

- Comparing the “Intervention Land Use Scenario” erosion and sediment delivery rates

with these from “2010 Land Use Scenario”, we noticed a hypothetical reduction of

11.4% in erosion rates, and a reduction of 52.5% in sedimentation rates.

Table 2 –Erosion and Sediment Delivery estimative in Cantareira Water Supply System at

current and post-interventions scenarios.

Cantareira Water Supply System

AREA (Ha)

Scenario Total Erosion (ton/yr)

Average Erosion (ton/ha/yr)

Total Sediment Delivery (ton/yr)

Average Sediment Delivery (ton/yr)

227,893 Current Land Use (2010)

4.122.730,3 18,09 591.928 2,6

227,893 Current Land Use (2010) considering interventions in priority areas

3.568.197,5 15,66 281.415 1,2

ABSOLUTE REDUCTION

469.360,1 2,1 310.513,0 1,4

PERCENTUAL REDUCTION

11,4% 11,4% 52,5% 52,5%

Map 2 – Priority areas identified at Cantareira Water Supply System

Discussion and Conclusions

We can notice that the hypothetical reduction in terms of sedimentation can be significantly

bigger than the erosion rate reduction; it probably happens because we are locating

restoration interventions at relative small but strategic portions of the watershed; despite the

fact that the erosion rate is not being dramatically reduced (because we are decreasing

erosion on a small portion of the whole system), riparian areas along water bodies and other

areas as steep slopes, if covered with forests or other natural vegetation, would trap most of

soil detached locally and upslope, and would avoid this eroded soil to reach lower portions of

the watershed, mainly water bodies. By doing this prioritized kind of intervention, we can

obtain impressive gains in terms of sedimentation reduction and water quality increase, with

smaller efforts of restoration.

Although we know we still need to calibrate Invest’s Sediment Retention model using field

measuring values (very hard to find in Brazil) for adjusting model precision, it already gives us a

very informative picture about the most expected benefit of restoration activities at Cantareira

System, that is the improvement of water quality by sediment reduction; besides that, Invest’s

Sediment Retention Model has proven to be a powerful tool for the Cantareira Project

restoration activities, by helping us to define the highest priority areas to continue expanding

our efforts towards the water ecosystem services improvement at Cantareira Water Supply

System.

REFERENCES

ISA (Instituto Socioambiental) -Cantareira 2006 : um olhar sobre o maior manancial de água

da Região Metropolitana de São Paulo / Marussia Whately, Pilar Cunha. São Paulo : Instituto

Socioambiental, 2007.

ISA (Instituto Socioambiental) 2012 – Cantareira System Land Use Map – 2012 Imagery

Natural Capital Project – InVest 2.4.2 Beta User’s Guide, 2012