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Urbanism

Floods: the waters find ways out

Projects for recovering green areas and the porosity of the soil alleviate the impact of the rains

Maria Gonçalves, from Ceará, 46-year- old, Ivoneide Palmeira, from Maranhão, aged 44, and George Duner, from São Paulo, 35 years old, pick kale, beetroot and corn from the garden that occupies a previously abandoned plot of land by the side of a viaduct on the main avenue of the East Side of the city of São Paulo. The three are part of a group of nine men and 12 women whose work in tilling the land, albeit occasional, is helping to avoid the sad spectacle that accompanies the end of year rains: rivers overflowing, flooded avenues, cars afloat, people clinging to posts so as not to be taken by the current, houses covered by the waters, and the traffic halted for hours, in cities transformed into lakes.

A reflection of deforestation and the construction of avenues, houses and factories on the plains besides the banks of the rivers, through which the excess rainwater would filter naturally, the floods are a national torment: in 1998 and 1999, 1,235 municipalities, corresponding to 22% of the total, suffered from rivers that overflowed and invaded streets and houses. At the beginning of this year, 338 municipalities from 15 states found themselves in a state of emergency, 84 people died, and 104,000 lost their houses because of the heavy rainfall, which begin now in September and goes on until March with growing intensity.

But some recent experiences indicate that floods are not necessarily inevitable phenomena like an earthquake. With the participation of the population, or through new laws, in cities beset by floods, like São Paulo, Porto Alegre and Recife, they are now trying to recover green areas, by creating vegetable gardens or restoring squares, and thereby to reduce the soil impermeability, one of the aggravating factors in floods.

When the soil is paved or covered with concrete, the volume of rainwater in circulation increases up to seven times, compared with uncovered soil. Without having anywhere to infiltrate, the water quickly goes on to lower ground, occupied in general by the poorer residents, the usual victims of the floods. In parallel with the effort of offering spaces for the water to infiltrate, the frequency of the floods has led to a conceptual revision: it is no longer thought that just the construction of large reservoirs for the temporary retention of water, the big pools, and the channeling of the rivers is going to put an end to the torture of the year ends and beginnings.

The same study that warned of the need for palliative actions in the East Side, the Environmental Atlas of the Municipality of São Paulo, made by a team from the city hall in collaboration with geologists, geographers, ecologists and engineers from the University of São Paulo (USP), substantiated the proposal for transforming into an area of environmental protection the initial stretches of the Aricanduva brook, one of the tributaries of the Tietê, the river that cuts through São Paulo, the largest city in the country, with some 10 million inhabitants and which is cut by other 3,200 kilometers of rivers and brooks, of which 400 kilometers are nor channeled.

“If this area is occupied, the works for lowering the bed of the Tietê river and the big pools will not be sufficient to contain the floods in the next few years”, warrants Patrícia Sepe, a geologist from the Secretariat for the Green and the Environment (SVMA) of São Paulo and one of the coordinators of the Atlas. According to her, the preservation of this area of 22.7 square kilometers, one of the last remnants of the natural vegetation of the Eastern District, has been a grievance of the inhabitants of the São Mateus district itself, in the debates for drawing up the Regional Master Plan, in 2002 and 2003.

In Porto Alegre, the capital of Rio Grande do Sul, the Urban Drainage Plan, approved in 2000, conditions the approval of projects for new housing lots to strategies for containing rainwater, by means of reservoirs or grassplots: the condominiums to be constructed cannot release to the neighboring land more water than before the construction. The strategies for fighting the floods sometimes are part of the master plans of the cities, approved from two years back, with the perspective of guiding urban occupation with a little more attention to the green areas and to contours than the previous plans, conceived three decades ago with an emphasis in the search for new areas for residencies or industries.

In some cases, as in the Metropolitan Region of Curitiba, in Paraná, in the city of Caxias do Sul, in Rio Grande do Sul, or in Santo André, in the São Paulo ABC region, and in Penápolis, in the interior of São Paulo, there are integrated plans for the networks for drainage, water supply, and sewage, usually built separately. They are tactics that promise lower costs and avoid the errors of the past. “Territorial planning can no longer take into consideration only the potentialities of natural resources, like contours, water, and climate”, comments Jurandyr Ross, from USP. “Attention should also be given to environmental frailties, that affect not only nature, but society in particular.”

There is no lack of laws. There never has been a lack. Luiz Roberto Jacintho, an engineer agronomist from the Secretariat of the Green in São Paulo, comments that the rains would not be enemies of the city dwellers if at least two federal laws had been respected: the Forestry Code, of 1965, according to which a swathe of 30 meters from the banks of the rivers should be left untouched, and one of 50 meters from the edge of the springs; and the Law on Building Lots (or Lehmann Law), of 1979, which established the areas of the cities to be occupied or otherwise.

“But, in the last few decades, because of demographic pressure, clandestine building lots have occupied the major part of the areas that ought to be kept free.” In 2002, the Public Prosecutor ordered the application of the Forestry Code in Recife, the capital of Pernambuco, with 1.5 million inhabitants, and located on the estuary of three large rivers and permeated by over 60 canals, with century-old flooding. The city hall accepted the decision of the Department of Justice, but the population protested: of the city’s 217 square kilometers, 70 were under the influence of the code and, of these, over half was already occupied by residences. Public debates ensued, and, in December 2003, after 41 drafts, the Municipal Chamber approved a conciliatory solution: there would be wider bands, from 40 to 120 meters, over that established by the Forestry Code, along the river banks still preserved, and some exceptions would be permitted, in the building lots already established or approved on the banks of the rivers, on which there was no more natural vegetation.

Recife also adopted a mechanism for compensation: those who build on the banks of rivers will have to recover a green area equivalent to twice the size of the lot – building a house on a lot of 300 square meters implies planting trees or creating gardens in 600 square meters of a square, a park, or edge of a watercourse. “We now have 40 projects at the stage of approval under the new law, each one of them implying the recovery of a thousand square meters, on average”, says Mauro Buarque, the director-general of the Secretariat for Planning, Urbanism and Environment. “In two years, when these areas have already been implanted, we have the expectation of far fewer problems with floods.”

Paradigm inverted
They are also changing the conceptual bases with which they are trying to solve the floods: no longer making the water run as quickly as possible to the rivers by means of canals – as strategy that, it is recognized today, merely transfers the problem to the neighboring regions -, but retarding the flow, by means of reservoirs and permeable areas. “The strategy of making the water flow away rapidly is totally wrong, for concentrating the inundation in a few points of the city”, comments civil engineer Carlos Tucci, from the Federal University of Rio Grande do Sul (UFRGS). “A good part of the current problems”, adds civil engineer Ricardo Bernardes, from the University of Brasilia (UnB), “is due to the distorted view that construction works would resolve everything.”

The old paradigm began to sink in the light of its own limitations. Twenty years ago, however much more brooks and rivers were channeled, there was no way of avoiding the floods in the central region of the city of São Paulo, the largest city in the country, where the city hall spends about R$ 200 million a year to allay the impact of the floods. In those days, the engineers found no way out other than building a gigantic reservoir to hold back the rainwater – and this is how the big pool in Pacaembu was born, the first in the country, inaugurated in 1995. Today, there are also big pools in Porto Alegre, Curitiba, Natal, Maceió and Teresina.

But however much they protect themselves, the cities will always be vulnerable to the effects of intense rainfall. “At some moment, any barrier will be overcome, because the rains can always be more intense than those taken into consideration in the engineering projects”, Bernardes says. At the beginning of 2004, the Aricanduva brook overflowed once again, as a result of excessive rainfall: it rained more in the first four days of February than during the whole month of February in each one of the two previous years. In the Northeast, the São Francisco River flooded in a way not seen for 18 years, and its waters occupied the streets and houses of 104 municipalities. Rivers that have been calm for years on end are sometimes dangerous as well, for suggesting that nothing abnormal is going to happen. In Santa Catarina, 70 years of relative tranquility gave the population the confidence to occupy the edges of the Itajaí and Açu rivers. In the great flood of 1983, Blumenau became submerged in the waters.

Today, the costs weigh against the old paradigm. “Channeling costs from three to ten times more than the construction of reservoirs, to solve the same problem”, says Tucci. According to a study by one of his students for a doctorate, Marcos Cruz, presented in June in the Municipal Chamber of Porto Alegre, the costs for controlling the floods in the Rio Grande do Sul capital by means of channels come to R$ 1.4 billion, while with sustainable measures – big pools, trenches, areas for infiltration, and permeable paving – would be R$ 221 million.

“While the rich countries found that the costs of channeling and conduits were very high and abandoned this kind of solution 30 years ago, poor countries are systematically adopting these measures, losing twice, with the higher costs and the increase of the damage”, says Tucci. According to him, the cost of channeling a kilometer of the Tamanduateí river, in the city of São Paulo, was US$ 50 million, and of the Arrudas river, in Belo Horizonte, US$ 25 million. “In both cases, the floods came back as soon as the works ended.”

The thief of savings
Years ago, Paulo Canedo, a civil engineer from the Federal University of Rio de Janeiro (UFRJ), handled the works against the inundation caused by three rivers in the municipalities of the Baixada Fluminense, in the Metropolitan Region of Rio de Janeiro. “Because of an absolutely predatory urbanization, there would be flood after flood”, he says. When he took office as president of the State Superintendency for Rivers and Lakes (Serla), in March 1991, Canedo halted the channeling works that had already been started and set out to study maps of the region, in search of alternatives. Canedo calls it luck the fact that he discovered an uninhabited area close to the springs of one of the rivers, the Sarapuí, which worked as a artillery test field for the Army. After some negotiations, he succeeded in getting authorization from the military to use this space as an area to absorb the floods.

Further along, he built a barrage of 7 kilometers in length, which held back the excess of waters from the Sarapuí and part of those coming from another river, the Pavuna, before reaching the cities. The cost of the work, US$ 12 million, was ten times less than originally forecast. There was also another gain, more subtle and profound. “Solving the floods”, he says, “we managed to break the perverse cycle of chronic impoverishment: every year, the inhabitants of the low-lying lands would get poorer, because they had to spend the small savings of the year to repair, albeit partially, the losses caused by the floods. Inundation was the thief that took their savings.” With the waters contained, he says, the inhabitants began to use their savings in refurbishment or in constructions, now done with new red bricks, no longer with old gray bricks as before.

Geologist Harmi Takiya – since 2002 at the head of one of the 31 regional city hall departments of the city of São Paulo, in Mooca, an area of 35 square kilometers with 308,000 inhabitants in the East Side – opens up on her desk the geological map of the municipality and shows that while the edges of the city are in high areas, with old plots of land, hardly inhabited and covered by natural vegetation, this region of the Eastern District is located on a plain subject to flooding, between the Aricanduva and Tamanduateí brooks, subsidiaries of the Tietê. Next, she turns to the satellite photos fixed on the wall. The vast horizontal housing condominiums are to be noted, and dozens of factory sheds, today abandoned in good measure, on Presidente Wilson avenue, close to the Tamanduateí river, and just one green patch, the Carmo Park, in Itaquera, some 25 kilometers from Mooca. “It’s an extremely arid scenario”, she says.

Over there, there really is very little green. In the environmental Atlas, which Harmi coordinated when she was in the Secretary for the Green, the districts of Brás, of Água Rasa and of Mooca (all in the Esat Side), which make up the regional department, appear with zero, 0.4 and 2.2 meters of green area per inhabitant, while in Morumbi, a high-lying district on the other side of the city, there are 239 meters of natural vegetation per inhabitant. Because of the scarcity of trees and the excess of concrete, the temperature of the Eastern District is one of the highest in the city: 32°C in Brás and 31.5o in Mooca, while in Morumbi the annual average is 27.5ºC.

Harmi availed herself of the Atlas, of the studies from the Secretariat for Planning, and of other databases to implant, jointly with the population, as series of measures that increase the permeability of the soil – some with a clear social impact. Added to the cleaning of the 20,000 street drains and the rain water galleries, for the rain to flow away instead of hampering people’s lives, was the recovery of public spaces: 51 of the 197 had already been reformed, and now, with earth and trees and less concrete, they acts as rainfall retention areas – in the whole of the municipality, with its 1,500 square kilometers, according to the Secretariat for Urban Infrastructure (Siurb), in the last few years, about 800,000 square meters of green area have been recovered, by means of the replanting of trees or restoration of squares.

In the East Side, at least two measures departed from the commonplace: the transformation of an abandoned area with 7,000 square meters alongside a viaduct into a vegetable garden maintained by 21 heads of family, who received an allowance of R$ 315 a month; and the Ecopoint, a center for taking in rubble, on which converge about 2,000 tons a month of leftovers from household repairs, wood scraps and old furniture that before would remain on the streets, clogging the drains, and contributing towards flooding – today they go directly to the city’s landfills.

At the meetings for drawing up the Regional Master Plan, “the major grievance of the inhabitants was precisely for more green and leisure areas”, says Harmi. “The sporadic interventions, like the green sidewalks proposed by the inhabitants of Tatuapé, with 40% of grass instead of cement, are a great help to hold back the floods.” According to Bernardes, from UnB, transforming into grass one third of a cemented area – on a simple sidewalk of a block or in a part of an urbanized area of the city – makes it possible to reduce by one quarter the flow of water that there would be if the whole area were to remain impermeable.

Quarrel between districts
Isolated actions, though, are not sufficient, Tucci warns. According to him, it is fundamental to administer the flow of water inside the compartments of the water basins – the sub-basins -, as is starting to be done in Curitiba and in Porto Alegre. But as the sub-basins can cover more than one district, it is not always easy to administer the conflicts that pop up. Until a little while ago, the inhabitants of the districts of Chácara das Pedras, Três Figueiras and Bela Vista, in the eastern portion of the capital of Rio Grande do Sul, refused to accept the transformation of some squares into reservoirs for the waters that overflow from the Areia river. In the first place, they feared lest they became garbage tips. Furthermore, they were not the ones that suffered from the floods, a worry only for the neighboring districts, located on lower terrain.

“There is no incentive for preventing floods, because there is a political gain”, Tucci criticizes, having studied the impact of rainfall in the country for 30 years. “When the municipalities go into a state of public calamity because of the floods, the mayors receive unbudgeted money that they can use without tenders.” Emergency actions also predominate in the federal sphere, although the Constitution attributes to the Union the responsibility for acting in a preventive way against droughts and flooding.

In January 2001, after the floods at the beginning of the year had affected almost 82,000 people in Minas Gerais, 8,200 in Rio de Janeiro and 9,100 in São Paulo, the then Minister of National Integration, Fernando Bezerra, recognized that the government ought to be prepared to face up to a problem that repeats itself. Three years later, in February 2004, the president himself, Luiz Inácio Lula da Silva, with six ministers, visited Petrolina, in Pernambuco, where there were 2,300 people homeless and 134 houses destroyed, and said that he was moved by the damage caused by the monumental flooding of the São Francisco.

Ideas from the countryside
The solutions against the floods also involve a revision of the role of the city dwellers. “Letting the rainwater that falls on the roofs and backyards run to the street, we transfer the problem to the public authorities, as we do with garbage and sewage”, explains Ross, from USP. For him, the owners of public and private spaces – and not just the new builders – ought to help to hold back the rainwater, installing more grassplots or reservoirs. These artifices for appeasing the rains meter by meter, drop by drop, by means of what the engineers call non-structural measures, used to be unacceptable. Ross was working as a voluntary advisor to the São Paulo Urban Planning Company (Emplasa) in 1985 when he took part in a pilot study to control the floods of the Cabuçu de Cima river, on the boundary between São Paulo and Guarulhos. He mapped the contours, analyzed the forms of land usage, identified areas subject to flooding and bottlenecks in the flow of water, and suggested that the owners of the buildings, houses and factories should build small reservoirs to hold back the flow of the rains. “They called me a madman”, he says. A suggestion that was dumped, of course.

In setting out his ideas, Ross remembered the time he was a lad, on a farm in the interior of Paraná, and would see his grandfather Thomaz Sanchez and his father Dionizio Hernandez, digging square holes in the ground to contain the rainwater, which afterwards would spread naturally over the coffee plantation. Much later, he discovered that the same technique is part of direct planting, in which you try to turn over the soil as little as possible, and to make the maximum use of water, inducing it to infiltrate, which at the same time improves the humidity of the soil and prevents erosion. “We have to interact with what happens in the countryside”, he says. “The engineers and the city dwellers could learn a bit more from farmers and rural engineers.”

The projects
1. Environmental atlas of the municipality of São Paulo; Modality Biota/FAPESP; Coordinator Harmi Takiya – SVMA; Investment R$ 148,845.00 (FAPESP)
2. Integrated planning for sanitation systems; Modality Regular Research Line; Coordinator Ricardo Silveira Bernardes – UnB; Investment R$ 100,000.00 (UnB)

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