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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.
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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
communities.
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Figure 8.24. The Upper Tiete River Basin and Surroundings
Table 8.9 - Growth of the urban area.
POPULATION URBANIZED 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
fold.
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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
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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
484
0
100
200
300
400
500
1893 1930 1977
Year
F
lo
w
(m
/s
)
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.
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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.
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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
failure.
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
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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
CHD
Telemetric network
other sources
TeleAccess
local researcher
CHD local network
Ponte Nova radar local network
normal link
contingency link
other sources
other sources CHD remote
operator console
TeleAccess
TeleAccess
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.
