Tuesday, March 23, 2010

Environmental Risk Assessment - Flood in São Paulo


8.5 The Metropolitan Region of São Paulo

by Benedito Braga

8.5.1 General Description

São Paulo Metropolitan Region is the largest urban conurbation in South America and the largest

industrial complex of Latin America. Its 16 million inhabitants spread over an area of

approximately 8,000 km, having 950 km2 of urbanized area, which is entirely comprised within the

Upper Tiete river basin, shown in Figure 8.23. The upper Tiete River basin at Edgard de Souza dam

has a drainage area of approximately 4,000 km2. Gentle slopes (of the order of 0.17 m/km)

characterize a meandering Tiete river. From its headwaters until Edgard de Souza dam the Tiete

river flows through 161 km, having as its main tributaries the Tamanduatei and the Pinheiros

rivers. The Tiete River basin is being urbanized at a very high rate upstream of Penha dam and is

almost completely urbanized downstream of this dam. Flood hydrographs for the upstream basin

show a slow rising limb with moderate peaks, typical of rural areas, while downstream of that

dam, flood hydrographs are typically urban. Due to the lack of adequate wastewater treatment,

these urban watercourses are highly polluted, conveying all sorts of municipal and industrial

wastes imposing thus a serious threat to human health and so, complicating even more the usual

flooding problems.

Figure 8.23. The Upper Tiete River Basin and The Metropolitan Region of São Paulo.

Although São Paulo Metropolitan region is geographically located in the tropics, its high

altitude (750 m) changes the climate of the region to Cwb (Koppen classification) that is, temperate

climate with dry winter. Annual average temperature is 19 °C varying from minimum of 15.5 °C to

a maximum of 25 °C. Due to the proximity of the region to ocean its average humidity is high (80

%). Its complex relief and the sea breeze bringing moist air in the afternoon facilitates the

occurrence of convective cells in the summer producing floods in small basins. Table 8.8 shows the

maximum 24-hour and monthly precipitation.


Table 8.8 Maximum rainfall in the Metropolitan Region of Sao Paulo

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Year 1949 1989 1949 1956 1941 1978 1976 1955 1966 1953 1978 1988

24 hours 146.4 104.3 93.9 84.8 71.0 94.6 74.9 67.2 64.5 72.4 108.4 131.9

Year 1947 1976 1948 1976 1987 1945 1976 1976 1941 1969 1978 1960

Month 483.7 520.2 381.6 215.3 277.2 208.9 167.1 152.9 250.6 256.2 638.2 385.5

8.5.2 Urban Drainage Problems

Ever since the beginning of the century a number of hydraulic structures have been constructed in

the basin. The main purpose of these hydraulic works was hydropower generation. Dams,

reservoirs and pumping stations were built so as to divert the flow of both Tiete and Pinheiros

rivers by impounding water at Edgard de Souza and pumping it back to Billings reservoir through

two pumping stations, namely Traição and Pedreira, as shown in Figure 8.24.

From Billings reservoir, water is transferred to Pedras reservoir from which electricity is

generated at Cubatão power plant at sea level, with a hydraulic head of 710 m. This large amount

of electric power available at the demand area allowed the growing of economic activities at an

exceptional high rate. Figure 8.25 shows the expansion of the urban area from the beginning of this

century. It can be noticed the importance of the energy availability in the expansion of the urban

area of the basin. In Table 8.9 it is shown the evolution of the population of the region which

jumped from a medium size city (300,000 inhabitants) in 1905 to a megalopolis of 16 million

inhabitants in 1995. Unfortunately, urban infrastructure did not improve at the same rate as

population and urbanization have grown in the region.

During large floods all runoff generated at the Pinheiros basin is pumped back into Billings

reservoir. Edgard de Souza spillway gates are opened so that the Tiete river flows according to its

natural east-west direction. This is a very sensitive system, which has to be operated with the due

forecast, since the backwater of Edgard de Souza dam reaches the downtown very populated area

of Sao Paulo.

From the scenarios previously outlined, two conflicting situations request urgent

treatment: the high water supply demand in contrast with low availability within the upper

Tiete river basin and the wastewater effluent that flows towards continental lands (following

the natural flow of Tiete river downstream) or towards the Billings reservoir through pumping

stations along Pinheiros river. The latter situation shall be gradually reduced with the multi-

billion dollar program of the State Government to clean up the waters of the Tiete in MRSP

(“Projeto Tiete”).

Grassroots groups representing the interests of the local population are trying to avoid

the wastewater disposal into their regions. Before 1992 the operational practice involved the

pumping of 50% of Tiete River flow at confluence with Pinheiros river (Figure 8.24) into Billings

reservoir and subsequent use for hydropower generation in Henry Borden power plant. Despite

the large active storage capacity of Billings reservoir (1.2 billion m3) it became a very large

oxidation pond. Thus the main problem associated with this way of operating the system is

anoxic conditions at Billings reservoir. On the other hand, if wastewater is discharged only to

Tiete River downstream, this presents a similar problem mainly for the cities along the water

course. After 1992, State Constitution provision imposed that, under normal hydrological

conditions, no water should be diverted to Billings reservoir. The only exception is during

flooding conditions when the Pinheiros channel capacity is limited by the backwater of the Tiete

River and for safety reasons water has to be pumped back to the Billings reservoir. The present

situation has transferred the problem of anoxic conditions of the Billings reservoir to the

reservoirs in the lower Tiete river downstream of the MRSP. The complexity is now even

greater because of the foam that is produced downstream of the spillways and reach riparian



Figure 8.24. The Upper Tiete River Basin and Surroundings

Table 8.9 - Growth of the urban area.


YEAR Million of

inhabitants Increment

(%) Related to the

basin (%) Increment


1905 0,3 0,6

267 433

1930 1,1 3,2

218 172

1954 3,5 8,7

166 154

1973 9,3 22,1

59 63

1985 14,8 36,0

72 30

2005 25,5 46,8

Due to inadequate land use in the basin, floods are becoming more severe in small creeks

and the problem is being transferred to the Pinheiros and Tiete river basins. The situation has

become extremely critical since the main freeways of Sao Paulo are located exactly at the banks

of the Tiete and of the Pinheiros rivers. During the wet period (December till March) the

population is frightened, radio, television and newspapers give much importance to the

problem. It is clear that any hydraulic work done in the Tiete or Pinheiros will be of little

efficiency in the future if flood control is not done in the contributing basins. Figure 5.26 shows

the design flows of the Tamanduateí river at Glicério (see Figure 5.22). It is clearly shown the

importance of source control. In less then a century design flows have increased more than five



Figure 8.25 Urbanization of Sao Paulo Metropolitan Area (1905 - 1995)

The silting of the macro-drainage system, mainly in the alluvial plain is another

important consequence of the inadequate land use in the basin. A 3.2 million cubic meters of

sediment with a dredging cost of US$ 36 million/year (Ramos et al., 1995) are important

expenditures in the State of Sao Paulo annual budget. Additionally there is the discharge of 50

m3/s of untreated urban and industrial waste water, to the drainage system. In this way, not

only the water but the sediment to be dredged is contaminated, and environmentally safe

measures have to be adopted to avoid impacts at the disposal site.

8.5.3 Structural and nonstructural solutions

Although the urban water management problems in the Metropolitan Region of São Paulo are not

new the solutions to these problems have only recently been implemented. The Department of

Water and Power of the State of São Paulo (DAEE) has recently contracted urban drainage master

plan, which should provide a comprehensive appraisal of the alternatives for the urban drainage


problems of the area. SABESP – Water Supply and Sanitation Agency of the State of São Paulo is

developing a multibillion dollar clean up of the effluent discharges from both, industry and

municipal wastes. This project involves the construction of some 15,000 km of collecting network,

315 km of interceptor mains and 5 waste treatment plants with total capacity of 60 m3/s. This

project will have a great impact in easing the pollution load in the streams during flood events.

Today, although the existing sewage control system is separated from the storm drainage system,

because of lack of treatment and illegal connections, a good portion of the pollution load comes

from specific sources such as municipal and industrial effluents.

60 120








1893 1930 1977








Figure 8.26 Design Flows of the Tamanduateí river at Glicério

As a mitigation measure a flood warning system has been established in the basin. The

pilot hydrologic telemetring system was installed by DAEE (Department of Water and Power of

the State of Sao Paulo) in 1977 with 5 stations: 3 raingages and 2 streamgages. The network has

been gradually expanded to reach its present 28 stations: 13 streamgages and 15 raingages. These

stations are distributed along the Tiete and Tamanduateí river basins. ELETROPAULO, the power

utility of the metropolitan region of Sao Paulo operates a similar network with a higher

concentration of stations in the Pinheiros river basin. These two networks are presently integrated

in such way that a total of 60 stations are available to real time rainfall monitoring in the upper

Tiete river basin.

All the microprocessors and the telemetry network were designed and developed at Escola

Politécnica by FDTE (Foundation for the Technologic Development of Engineering) and CTH

(Centro Tecnológico de Hidráulica). Basically the rainfall sensor is a traditional tipping bucket

gage that is coupled to a reed relay. Each time the bucket fills it tips up and closes the contact of

the relay indicating 0.1 mm of rainfall. The water level transducer is made of an aluminum disc

and a sensor, coupled to a traditional streamgage of the float type. A variation in water level

rotates the pulley and the disc. The parameters are such that a 1 cm change in level rotates the disc

by 18 degrees, thus moving one radial piece to the position of the next. The sensor comprises two

reed relays and a permanent magnet mounted in such a way that a magnetic circuit closes

through the radial iron piece that lies in front of the sensor. The reeds are located in such a way

that they close the contacts in a sequence that depends on the sense of rotation of the disc.

The transducers are connected in the field to a remote station which is an electronic

equipment that stores locally the hydrologic data, releases these data to the base station upon

request, interfaces with the communication lines (telephone and UHF radio) and protects

electronics from lightning. Up to 8 transducers can be simultaneously connected to a remote

station. The remote station has an autonomy of 48 hours in the event of a power failure.

All the telemetring information is concentrated on a base station that manages the entire

network, interrogating sequentially the remote stations at 5 minutes time intervals, transmitting

control and scheduling messages and allowing the operator access all information and to request

specific tasks. The base station performs consistency checks of the data collected.


Rainfall Monitoring

In 1988 through an agreement between DAEE and FAPESP (Fundação de Amparo a Pesquisa do

Estado de São Paulo) a weather radar was installed in the Ponte Nova reservoir east of São Paulo.

This equipment developed and installed by McGill University of Montreal, Canada allowed a

much more refined estimation of the precipitation field in the Upper Tiete River basin. Given the

local climatology, where heat island effects and the sea breeze from the nearby ocean bring a

variety of weather variability, it was decided to purchase a system with low attenuation and high

4-D resolution.

The radar installed in Ponte Nova is an S band radar (3.0 GHZ) that allows the monitoring

of reflectivity factor in 2 km x 2 km for a radius of 240 km around its center. Rainfall rates greater

than 0.3 mm/h can be estimated using any specified Z/R relationship. DSD from disdrometric

measurements are being conducted for adequating the Z/R relationship processes involved in the

radar operation are depicted. The radar signal is a high power magnetron generated and

transmitted through a 2° HPSW. The received signal is digitized using a McGill DVIP and the

data is stored in magnetic tapes using a LSI 11/73 Digital microprocessor. An antenna program

with 20 elevations is performed in 3 ½ minutes and repeated every 10 minutes. During 6 ½

minutes the processor computes CAPPI, ECHOTOP, cross-sections, rainfall accumulation maps

and very short range forecasts for selected sites. These 2 km x 2 km resolution maps which covers

a 360 x 360 km surveillance area, are sent through telephone lines to the Center for Hydrologic

Data (CHD) at CTH - University of São Paulo.

In 1994 a research project submitted to FAPESP by IAG and CTH proposed the

modernization of the existing system through changes in the existing hardware and software

(Massambani, Braga and Barros, 1993). New systems with 486 platforms and INDY workstations

will be operational by the end of 1995 keeping up with the new technology available. The

following improvements will be available in the new system: a)-replace existing LSI-11 based

computer by a PC for antenna control and data acquisition and a Unix-based workstation for

calculations and graphics displays. This will allow for lower maintenance costs, faster

acquisition/processing cycle (from actual 10 minutes/cycle to 5 minutes/cycle), enhanced spatial

resolution (from present 4km X 4km to 2km X 2km), more processing power to run on-line

forecasting models; b)-replace existing communication protocol to CHD (Center for Hydrological

Data) from a proprietary to a wide-used standard (PPP), to lower maintenance costs (specialized

personnel) and to enhance availability (a private line and a dialed line instead of only one);c)-

replace existing digitizer electronic card by a commercial product, easing maintenance;

Macro scale qualitative information from weather satellite GOES is received on a daily basis from

IAG/USP. A five day forecast from NMC-Washington is used to guide preparedness measures in

the civil defense area. Several studies have being performed integrating radar and satellite

information, using VIS and IR digital from GOES and METEOSAT to discriminate the raining

from the non-raining area. RAINSAT techniques as described in Bellon et al.(1980), CST in Adler

and Negri (1988). Microwave (Negri et al., 1994) has also being applied to the radar data seeking

better description of the raining area outside the radar range.

Rainfall and streamflow forecasting

While it is very important to monitor rainfall and water levels in rivers and reservoirs, if this

information is not used to forecast their future values it is useless. The way flood levels are

forecast involve some type of hydrologic modeling. Three approaches have been attempted in the

Sao Paulo Flood Warning System. For the city of Sao Paulo a semi-empirical model was

developed for forecast in areas without streamgage information. A linear stochastic model is

being calibrated to the Tiete river at Limão streamgage (Figure 8.22) and a more complex

hydrodynamic model is being developed for the Meninos River at the junction with the

Tamanduateí river. In order to have larger lead forecasting times it is necessary to forecast rainfall.

Currently the SHARP technique (Bellon and Austin, 1978) is being used with some success.


Improvements are needed to cope with tropical thunderstorms that develop over the watershed

during the day in the summertime

Radar reflectivity at a constant altitude plan (CAPPI) of 3 km is converted into rainfall rates

using the Marshall-Palmer relationship. These rainfall rates are computed for all pixels within the

radar range. The Mean Displacement Vector – MDV (Austin and Bellon, 1982) computes the

advection vector for the whole rainfall field within the radar range. This is done through the

computation of the maximum spatial correlation for two consecutive CAPPIs at 10 minute time

interval. This technique is applicable in the case of systems already developed, such as fronts and

squall lines. In tropical countries, however, due to the high frequency of convective storms the

technique cannot be applied in the form developed. MDV and the real time rainfall rate field

(dbZ) are used to numerically solve a 2-D conservation equation for rainfall forecasting (Braga

et al., 1998)

Three models have been developed to forecast micro, meso and macro drainage flooding

in the Metropolitan Region of São Paulo. The micro drainage problem is related to local floods

at the range of street blocks. These forecasts are based on rainfall directly using the an heuristic

procedure described in Braga et al., (1998). The meso and macro drainage modeling is

performed through the use of variations of linear stochastic models with exogenous variables

(rainfall) (Braga, Barros and Marcelini (1992))

8.5.4 Information Management System

The information Management System used in the the DSS (Massambani, Braga and Barros ,1994)

has a CHD (Center for Hydrological Data) as an on-line hydrological database for present and

past events. As depicted in Figure 8.27 it connects: the meteorological radar in Ponte Nova, the

telemetric networks, the forecasting models and other sources of information. This allows all the

users of the system to have an unified interface.

CHD keeps recent data (about last 2 months) in magnetic storage, updating information

from radar, telemetric network or other sources of information. A special data format is being

specified to allow gathering information into CHD in a organized way. Older data will be

further classified in "significant events", allowing for a fast retrieval from optical disks by

meaningful names, or marked as "ordinary events" to be retrieved by date/time. This older data

will be kept in optical midia.

Access to this information is done through regular INTERNET channel featuring:

information retrieval from CHD; layered views of information, including geographical, river

stages, precipitation and others displayed and manipulated as follows; zooming; animated

simulation, including interpolation and extrapolation of/between events; alarms associated to

events; interfacing with MS-Windows DDE applications (such as MS-Excel or a user

application) allowing for local processing; among others. Finally, the CHD remote operator

console eases operational procedures, allowing for a remote support to operate CHD in case of


8.5.5 Conclusions

Flood control represents one of the most critical issues in urban water management of the

Metropolitan Region of São Paulo. This paper gave a retrospective view of the flood control

problems of the MRSP and some of the recent measures taken by State authorities which

include among others the development of an urban drainage master plan for the Upper Tiete

River Basin. A flood warning system that started in the late 70’s has proven to be a very

effective nonstructural alternative for coping with urban floods in the basin.

The system has evolved in recent years to a powerful Decision Support System which

provides users with reliable information in real time via INTERNET channel. It is a very

important social component in the sense that it provides the State and municipal civil defense

means of mitigating the floods effects on the riverine poor people of the region. Moreover when

one considers that raw sewage flows in all creeks and rivers in the region it becomes extremely


important to have a reliable forecasting system. The forecasting system is in operation since

1976 and its performance was greatly improved in 1988 with the installation of a weather radar

in Ponte Nova dam.

local researcher

local researcher

Ponte Nova radar


Telemetric network

other sources


local researcher

CHD local network

Ponte Nova radar local network

normal link

contingency link

other sources

other sources CHD remote

operator console



Figure 8.27 - The new Center for Hydrologic Data - CHD

New improvements are being made to the existing system including updated software

and computational techniques. From the technological point of view, this new system puts

together low cost PC-based data servers and medium-to-high end workstations, in a networked

environment thought with availability, open-system standards and operational costs in mind.

All this together makes this architecture a reference for similar projects.

No comments:

Post a Comment