Decision Support System for Urban Water Management Barros1, M.T.L., Brandão2, J.L.B. and Hamburger3, D. 1
Associate Professor, University of São Paulo, ph. 55 11 3021 1005, email:
[email protected] Graduate Student, University of São Paulo, email:
[email protected] 3 Researcher, University of São Paulo, email:
[email protected] 2
Abstract São Paulo is one of the biggest cities in the world with ten million inhabitants living in a degraded urban environment. São Paulo urbanization process has been chaotic without planning and control. Today the city is facing a lot of problems, many of them related to its water resources. The population growth and the urbanization process generate many negative impacts in the watersheds: pollution, floods, erosion, water supply deficits, etc. The rivers crossing the city are complete polluted due to domestic sewage. Less than fifteen percent of the sewage is treated. During the rainy season, from November to March, the city suffers a lot with flash floods. There are more than 500 flood areas in the city. The water supply system is in the maximum production and the city is subject to water shortage during the dry season. The new projects to attend the water supply in the future are very expensive and will generate many impacts in the neighbor basins. In summary São Paulo water resources problem is very complex and will demand a lot of investments to modify this situation. Decisions in the water resources projects will involve social, economical and environmental aspects. A research study on São Paulo urban water management has been conducted by the University of São Paulo (USP), Civil Engineering School. A small urban catchment was selected for case study, the Cabuçu de Baixo River basin, which manifests very well the present situation in São Paulo. The project aims to analyze many subjects: urban hydrology, storm drainage systems, nonpoint source pollution, erosion and sediments, urbanization indexes, housing problems, etc. The results of this study are been condensed in a Decision Support System (DSS) for urban water management. Introduction São Paulo is the biggest city in South America and it is between the ten biggest in the world. The city is located in the Tietê River Basin, one of the left tributaries of the Paraná River. The Upper Tietê River drainage area is 5,755 square km. 69% of the São Paulo Metropolitan Area (SPMA) is located in this basin. SPMA has 39 municipalities with 17 million inhabitants. Figure 1 shows the SPMA and its position in Brazil and in the State of São Paulo. At the same figure, it can be seen the SPMA municipalities and the Upper Tietê basin. The river is located in a plateau 700 meters high, in average. The Tietê River goes from east to west crossing the State of São Paulo. Between the plateau and the Atlantic Ocean there is a range called Serra do Mar. The Upper Tietê has slight slope, 15 cm/km in average, in opposite some of its tributaries are very steep. Due to this, Tietê River is a typical smooth water course with large flooded areas. The hydrology in this region is seasonal, the rainy season occurs from October to March and the dry season from April to September. The mean annual rainfall is 1300 mm, typical volume observed in sub-tropical regions. The Upper Tietê basin has been occupied in chaotic way. In year 1900 the São Paulo population was 200,000 inhabitants. Today, 17 million inhabitants live in this region. The São Paulo city
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population itself is 10 million inhabitants. SPMA is the greatest industrial and commercial area of Brazil. São Paulo State has the second budget of Brazil and SPMA produces 52% of its economy. The development of SPMA is in part due to its water resources. At the forty’s a huge hydropower system (816 Mw of installed capacity) was built in the São Paulo coast using the 700 meters of head existing between the city and the costal area. At this time, part of the Upper Tietê River was deviated to produce energy. Until today this hydropower system is one of the highest in the world (Cubatão Hydropower Plant). During this time São Paulo increased its industrial production and, due to this, its population, with migrants and emigrants from many places.
Figure 1 – São Paulo Metropolitan Area (SPMA) and Upper Tietê River Basin The population growth was responsible for the chaotic process of the Tietê’s environment devastation. The urbanization process occurred without planning. Particularly, the water resources were tremendous affected by this intense growth. São Paulo is facing today problems related to its water resources: water supply shortages (domestic and industrial), water quality deterioration - the rivers are completely polluted -, storm drainage problems - many floods occur every year all over the metropolitan area. The urban infrastructure of São Paulo did not follow the city growth. The lack of planning and investments in water works are responsible for this situation. The water supply system covers almost all residences but the distribution system is not efficient with high index of losses, more than 30%. The sewage is collected in 70% of the residences but less than 15% is treated. The domestic sewage is dumped to the rivers without any kind of treatment. The São Paulo storm drainage system is old and do not have enough capacity to attend the impermeable area growth. São Paulo has more than 500 areas subject to floods. The flood damages
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are enormous, generating huge social and economical losses. The traffic, the houses and the industries are severely damaged every rainy season. Beyond the water problems, the region faces critical social problems generating negative environmental impacts. In general, the SPMA standard of living is very low. The housing problem is particularly critical. São Paulo has today two million of unemployed and more than one million people living in shantytowns (favelas). Many of these favelas are located in risk areas, riparian areas or steep mountains. During rainy days, these areas are tremendous affected by flash floods and landslides. People living in these areas suffer a lot not only with diseases like leptospyrose, but also with material damages. Is very common in hard rain events the occurrence of deaths by drowning and collapse of houses. Another critical problem in São Paulo is the garbage and sediments that reach the drainage systems and channels. The garbage collection is inefficient, mainly in shantytowns. Therefore, a lot of discard materials is thrown away into the storm drains obstructing them. The erosion process in steep mountains is intense producing high volumes of sediments. When it rains, soil and debris from these areas are eroded and washed into streams. The state agency for flood control spends a lot of money in dredging the Tietê riverbed every year. The project The origin of water resources problems can be attributed, in general, to the lack of planning. Considering the new water management policy in Brazil, the water resources planning studies start to have major importance. According to the law of waters in the State of São Paulo, the water resources management is coordinated by Watershed Committees. The Committee is formed by representatives of the government, the cities and the civil society. The main activity of the Committee is to decide for the priority of water works and management programs defined by the Watershed Master Plan. The money to make the plan possible (budget) comes from many sources, one important is the water charge. The water charge is a new concept in Brazil and in a certain way in many countries. The Brazilian water law establishes that the water is a public good and it has to be available in quantity and in quality for any person. By this concept any user has to pay for water in order to keep it clean and for anyone. The water charge money has to be applied in the same basin that it was collected. To implement the water charge the watershed committee, among other things, has to maintain a system to manage the uses, demands, etc. Therefore, an activity necessary to improve the management and control of water resources is to create and to keep an efficient information system, as much in terms of quantity, as of quality. The State of São Paulo has developed its Watershed Master Plans with many technical problems. In general, the studies have faced serious problems of data availability. The management of the urban water is more complex because it involves many interfaces, beyond those directly on to the water resources. In the case of São Paulo, the problem is still more complex, considering the aspects previously pointed out. Considering the importance of this problem, the National Agency for Scientific and Technological Development (CNPq), through the Environment Science Program, and the Federal Water Resources Fund are sponsoring a research on the urban water management. The main objective of this project is to establish a general methodology on data and mathematical modeling analysis to support water resources planning. Many aspects are considered in this research, such as: • •
Dynamics of expansion of the urban spot; Impacts of the Urbanization in the Hydrology (quantitative aspects);
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• • • •
Impacts of the Urbanization in the Urban Drainage System; Impacts of the Urbanization of the Quality of the Water (nonpoint source pollution); Impacts of the Urbanization in the erosion and in the sediment yields; Development of decision support system for urban water management.
As it can be observed, the research involves many subjects, but it emphasizes the importance of the urban environment monitoring system and a systematic way to analyze data and models. Given the extension of Upper Tietê´s area a small sub basin was selected as a case study, the Cabuçu de Baixo River basin. This basin was selected by its characteristics. It represents very well the water resources problems in São Paulo. Cabuçu de Baixo River Basin The Cabuçu de Baixo River is a tributary of Tietê River. Figure 2 shows its basin and its position in the Upper Tietê River basin. Its drainage area is 41.96 square km with slopes varying between 2.8 and 1.1%. The mean annual rainfall is 1620 mm. The basin can be divided in five sub-basins: Bananal River, Itaguaçu River, Guaraú River, Bispo River and Cabuçu de Baixo River itself. Figure 3 shows these sub-basins.
Figure 2 – The Cabuçu de Baixo River and the Upper Tietê River Basin
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Figure 3 – The Cabuçu de Baixo Sub Basins It is very important to point out the difference between the landuse characteristics in these subbasins. Bananal, Bispo and Guaraú basins are in process of urbanization with many illegal shantytowns and dense urbanization with high index of impermeable areas. Itaguaçu basin surface is still totally covered with natural tropical vegetation. Cabuçu de Baixo Basin is almost completely impermeable. Figure 4 presents some pictures showing different landuses.
Figure 4 – Different landuse at the Cabuçu de Baixo River Basin Figure 5 shows an IKONOS image taken in year 2000. The different landuses can be seen clearly in this picture. The upper part of the basin (in green on Figure 5) drains a mountain range called “Serra da Cantareira”. This area is officially preserved. However, some areas are in intense process of illegal occupation (Bananal and Bispo basins). From upper part to downstream, the basin is completely urbanized with high indexes of impermeable areas.
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Figure 5 – Cabuçu de Baixo Basin in year 2000 (IKONOS) Dynamic of Urban Expansion This part of the study has several objectives: understand the urbanization process and the expansion of the urban spot, define a landuse classification that can be used for different purposes, classify the landuse according to this criteria, classify the landuse in time and create a dynamic data bank. The analysis has been done using remote sensing technique with images taken in different dates and by different satellites. There are Landsat TM images taken in 1985, 1990, 1994 and 1997 and a SPOT panchromatic taken in 1995. For year 2000 there are two images, one from IKONOS and another from Landsat ETM. A set of field and social and economical data has been raised. The landuse classification was done following the hydrological and nonpoint source pollution studies. The classification was done considering 17 different types of landuse. Considering the dynamics of change in landuse and with IKONOS image was possible to model the process. Following the Jensen and Toll (1981) methodology, was possible to describe the expansion and the urban density. Three processes were considered important to verify the basin permeability variation: the increase of built area, occupation of vacant lands and urban expansion. Figure 6 shows (in red) the urban expansion during the 1985-1997 period. Other important landuse changes during that time were the garden growth and the implementation of detention basins. Two
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detention basins were built in recent years, one at the Bananal River and another one at the Guaraú River. The purpose of them is to control floods along de main course of the Cabuçu de Baixo River.
Figure 6 – Urban Expansion in the Cabuçu de Baixo River Basin (during 1985-1997 period) Water Quantity and Quality The quantity and qualitative analysis are been conducted in three areas: hydrology/hydraulic, nonpoint source pollution and erosion and sediment transport process. To make possible the research, was necessary to install a monitoring system with raingages, streamflow stations and water quality data collection sensors. In terms of rainfall monitoring, four raingages (tipping buck type) were installed. In the future these gages will be incorporate to the Tietê telemetric network. Figure 7 shows the raingages distribution. The basin is also monitored by the meteorological radar system of SPMA. There are radar images available every five minutes in a grid of 2 km by 2km.
Figure 7 – Cabuçu de Baixo Rainfall Network For streamflow measurements five stations were installed. The stations were installed in strategic locations to control three sub-basins: Bananal, Itaguaçu and Cabuçu de Baixo, considering three different landuses. The objective is to compare the hydrology of these basins. Itaguaçu is still natural, Bananal is in process of urbanization without planning (illegal occupation) and Cabuçu is
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completely urbanized and impermeable. Another interesting subject is to evaluate the effect of the detention basins to control floods. A new detention basin was built at the Bananal River to control downstream flood areas. Two stations were installed in Bananal River, one upstream to measure the inflow to the detention basin and another after its spillway. Figure 8 shows the streamflow stations. It can be notice by this figure the poor hydraulic condition in the Bananal River due the garbage and the instability of its channel. In the Itaguaçu River was possible to install a weir to measure the flow with high precision.
Figure 8 – Cabuçu de Baixo Streamgage Network The stormwater analysis has been made applying the Soil Conservation Service (SCS) method (USDA, 1973). Therefore, is important to establish the relationship between landuse and the Curve Number (CN), parameter which defines the runoff volume. A set of CN maps was made for the sub basins considering geology, landuse and impermeable areas. A hydraulic model for channels and rivers was developed considering the full set of Saint Venant Equations. The hydrological and hydraulic set of models was designed by the Hydraulic Technological Centre Foundation (FCTH, 2002), a research laboratory linked to the University of São Paulo and to this project. The streamflow network has been also used for water quality measurements. The water quality parameters are been calculated by the traditional technique (data field collection and laboratory analysis) and by automatic sensors (Data-Sonde Hydrolab 4A). There are two basic objectives in this study: evaluate the nonpoint source pollution and the sediment yield affluent to the channels. The measurements have been made in dry and rainy seasons, in order to make comparisons and to evaluate the nonpoint yields. It is important to remind that the rivers in this basin are completely polluted by domestic sewage with exception of the Itaguaçu River. In terms of nonpoint source pollution, the research intends to establish the relationship between pollutants and different uses of urban areas. The following parameters have been measured: BOD, COD, pH, ammonia nitrogen, soluble phosphate, total phosphate, MSH, total suspended solids, fixed suspended solids, volatile suspended solids, total solids, fixed solids and volatile solids. The sonde can measure DO, conductivity, pH, temperature, oxides, nitrates, chloride and turbidity. Figure 9 presents some
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recent results observed in the Cabuçu de Baixo River. The nonpoint source pollution mathematical model analysis is to be done with the Basins 3.0 model (USEPA, 2001).
Figure 9 – Parameters for Nonpoint Source Pollution Measurements Cabuçu de Baixo River The results show the difference between hydro (blue) and pollution (green) peaks. The effect of the nonpoint source pollution is considerable at the Cabuçu River The erosion and sediment yield will be evaluated by empirical multiple non linear regressions to establish relationships between occupation, erosion and suspended sediment flow in the channels. The project aims also to suggest structural and non structural measurements to minimize erosion and sediment yields. The Decision Support System The data and model sets will be linked in a DSS to support the urban water management. Figure 10 shows the basic DSS frame. Presently, the DSS is been programmed and some parts can be seen in the internet address: www.poli.usp.br/cabucu in Portuguese.
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Figure 10 – DSS for Urban Water Management The DSS will be structured with three modules. First is the visual interface, where the user can be manipulate the DSS, for example access a data bank, verify reports, graphs, tables, run mathematical models, access the GIS data bank, etc. Second module is the modeling set, which can be accessed in order to analyze the behavior of the basin considering historical and new cases of hydrology/hydraulic, nonpoint source pollution and sediment transport conditions. Third module is the data bank, composed of historical and dynamic information, the user can access the bank to collect or to update information. The DSS is using a GIS system developed by INPE, this software is called SPRING (INPE, 2002). Figure 11 shows an example of the DSS application: impact of the landuse in the runoff volume. This can be done changing the CN parameter in certain grids. The user can choose one of the sub-basins and indicate a new use. After he can run historical events or choose a new event by his own and evaluate the CN impact.
Figure 11 – DSS Structure for CN Maps Figure 12 presents the DSS frame for the mathematical models.
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Figure 12 – DSS Mathematical Models Set In the future, this DSS will be linked with other urban infrastructure systems, mainly with the DSS that controls the São Paulo Flood Forecasting System (www.saisp.br). Finally, it is important to point out the value of this DSS in the context of the urban water management in Brazil. As was mentioned before, the municipalities and other agencies do not have enough tools to handle with water problems. This kind of system, besides its technical value, stands out the importance of the data (collection and storage) bank and the use of mathematical models in water management planning and control. Until now, there is a certain distance between the academic work and the activities carried through the management agencies for water resources. The main objective will be reached if this DSS will be able to modify this situation. ACKNOWLEDGEMENTS The research reported herein is supported by Brazilian CNPq/CIAMB PADCT III Program under award 01/97-03/01-2. To the consulting USP team: Dra. Monica Ferreira do Amaral Porto, Dr. Luis César de Souza Pinto, Dr. José Alberto Quintanilha and Dr. Witold Zmitrowicz References FCTH Manual dos programas CABC e CLIV, 2002, home page: http://www.fcth.br/software/software.html . (in Portuguese). INPE Manual do Spring versão 3.6.02, 2002, home page: http://www.dpi.inpe.br/spring/ . (in Portuguese). JENSEN, J.R.; TOLL, D.L. Detecting residential land use development at the urban fringe. Photogrammetric Engineering and Remote Sensing, 48(4):629-643, Apr.1981. USEPA (Environmental Protection Agency), Basins 3.0, 2001, home page: http://www.epa.gov/waterscience/basins/basinsv3.htm USDA Soil Conservation Service, National Engineering Handbook, 1973.
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