Towards Sustainable Urban Water Management in Brazil

Towards Sustainable Urban Water Management in Brazil

Bakker, E.F.

Sanders, F.M. (mentor)
Tucci, C.E.M. (mentor)
Van de Ven, F.H.M. (mentor)
De Boer, E. (mentor)

Civil Engineering and Geosciences

Transport & Planning

2009-02-02

The ongoing increase of imperviousness in urban areas and the increase of heavy storm events trigger the urge for more sustainable urban water systems to combat flooding in Brazil. In developed countries source control measures have been developed to combat the negative impact of these two factors and more sustainable urban water systems are developed. In developing countries, however, this is not the case. Most solutions in developing countries still focus on end-of-pipe measures. Rapid urbanization during the last decades, without adequate urban planning, has resulted in severe hydrologic and environmental impacts in Brazilian cities. This has already led to drought and flooding problems. Continuing this developing pattern, by increasing the imperviousness in urban areas, as well as expanding cities by low-density developments, will lead to exacerbation of these problems and does not lead to a sustainable water system. The sanitary philosophy, by which urban drainage systems are based on the concept of draining the water from urban surfaces as quickly as possible, is still much applied in Brazil. Canalization of urban streams, clandestine urban flood plain occupation, a lack of environmental awareness, a large sediment production and a large amount of solid waste disposal into the drainage system have lead to a systematic degradation process of urban streams. The triplet applied in The Netherlands of first retaining, then storing and ultimately discharging of stormwater contributes to a more stable urban drainage system. Measures like bioretention cells, infiltration trenches, green roofs and micro-reservoirs are getting more and more common practice in drainage systems in developed countries. Through a case study in a 6 km2 urban catchment (part of the Arroio da Areia catchment) in the city of Porto Alegre, the influence of different drainage approaches on the runoff is assessed. The catchment is modelled with the SWMM5 stormwater model, applying the kinematic wave approach. By modelling the current drainage system the bottlenecks are identified. In the current situation flooding occurs in 14 of the 31 nodes when modelled by a 10-year return period storm. The total flooding volume accounts up to almost 30,000 m3. The construction costs of the current macro drainage system are estimated at R$ 14.3 M. The objective of this case study is to present and assess alternative drainage approaches to combat these flooding problems and to present recommendations for future developments. It is shown that enlargement of the conduit diameters in the current drainage system layout to combat flooding is almost 2 times more expensive than solving the flooding problem by implanting detention basins or by adopting low impact development. It is also shown that the peak runoff produced by enlargement of the current drainage system is between 1.5 to 2 times higher than the peak runoff generated in case detention ponds or low impact development is adopted. It is concluded that by continuing development in the conventional way, by accelerating discharge of runoff and building low-density neighbourhoods, costs for society as well as the impact on the environment and on the liveability in the city are redundantly high. It is recommended that low impact development demonstration projects should be developed to build capacity among urban water and drainage professionals, in municipal departments as well as among companies active in the sector, and to increase awareness about the environment among the population.

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Student theses

master thesis

(c) 2009 Bakker, E.F.