The City of Nairobi, Kenya lies at the border of the central highlands and the flat dry plains, composing an exceptionally interesting subtropical highland climate. This translates to two rainy seasons with an average annual high temperature of 280C and a low of 150C. The southern sloping terrain enables a natural drainage flow that settles in the southern plains, causing occasional flooding.
During the rainy season, flooding may be experienced in other parts of the city. The bulk of the blame here is placed on lack of drainage infrastructure during road construction and maintenance, developments along riparian reserves, and newly built up areas that block natural water flows. Like many developing cities, rains here are associated with floods.
Drainage in the informal settlements is worse due to haphazard development and construction without consideration of natural water flows, riparian reserves and wetland management.
Urban planners the world over are now considering the use of Sustainable Urban Drainage (SUDs). SUDs involve draining urban areas, enabling proper and practical re-use of water - rather than routing it through a pipe. SUDs include the use of permeable paving and naturalized swales. Practical methods also see the application of tree pits to drain roads, recycling of water for other uses, underground storage of rainwater and community spaces. New developments that involve surface water drainage are expected to ensure that they pass through SUDs.
In urban areas, like the City of Nairobi, rainfall management ought to be viewed as an exciting opportunity for SUDs. Water harvesting, damming of water, and wetland management can be easily practiced at community levels to promote and increase the availability of potable water, while reducing runoff. Development of city drainage can be done in a manner that resembles the water cycle taking into consideration runoff, waste water, supply and demand, environment, community and the local character of a place. Unfortunately, rain water is seen as a nuisance and not a potential resource resulting in the poor management of storm water.
In many cities, the risks that floods pose are taken lightly. Only after heavy rains is there talk of something that should be done. Preventative management is rarely considered and researchers are proposing an urban drainage evaluation followed by selection and implementation of flood prevention procedures, feedback and evaluation.
A good example of proper management of urban rainwater was in Curitiba, Brazil. Lying on a river basin that floods regularly, floods caused more than $40 million of damages in 1995. The authorities opted to create large public parks along natural waterways as a method of water stabilization. An artificial channel was also dug to help increase the river capacity and act as a border to prevent growth into the park.
Developing cities, however, still face various socio-economic factors that make it difficult to solve urban drainage. The challenge of informal settlement problems, together with poor urban philosophical design and contamination of storm runoff from sewage or garbage, poses a major risk. There is also poor authority and community interaction towards obtaining solutions and lack of technological basis in drainage management and design.
What would be the best way of dealing effectively with urban drainage in developing cities? How can the built environment evolve without ignoring natural forms like the hydrological cycle and natural water flows?
Credits: Images by Constant Cap and South C Ward. Data linked to sources.