November 23rd 2017

Society / Environment

Ongoing rains should catalyse our solutions for flooding in Nairobi

Impervious surfaces like concrete do not absorb surface runoff. Rather, they redirect rainwater to drainage systems which are often clogged with debris and solid waste hence causing floods. To correct this issue, permeable surfaces are recommended. Permeable surfaces are characterized by more vegeta

By Angeline Mbogoangelinejaymz@gmail.comTuesday, 07 Nov 2017 06:53 EAT

Nairobi floods can be contained with proper planning.

The rainy season is with us again and Nairobi has experienced quite a little bit of flooding, though not on a destructive scale yet. The relationship between floods and the built environment is known all over the world, and it is high time our city planners took steps to mitigate the effect of floods in Nairobi.

A study that examined the impact of the built environment on flood losses in Texas stated that: “The relationship between urban development and flooding depends on the amount of impervious surface generated. When urbanization and associated impervious surface coincide with the alteration of naturally occurring wetlands, flooding can be further accentuated.”

This statement is true also for Nairobi which constantly experiences floods contributed by urbanization. The increased demand for land has seen developers construct homes on wetlands in areas such as Kileleshwa and encroach on the Mbagathi River floodplains. Similarly, roads and pavements have been constructed without providing adequate drainage for surface runoff.

Hence, whenever it rains heavily, Nairobians will spend hours on flooded roads en route home from work or school. Moreover, vehicles, homes, and other properties attract heavy costs due to damages. Sometimes, a life might be lost as well. It is worth noting that the greatest losers during floods are the slum dwellers. Flooding in slums is as a result of house construction on floodplains and inefficient drainage systems often blocked by waste.

Thus, in view of this hazard, certain solutions should be prioritized. One such solution is the creation of a sponge city. A sponge city can hold, clean, and drain water naturally. The sponge city concept is being adopted in China, a country that often experiences urban floods.

Unlike Nairobi that does not trap rainwater, a sponge city retains its rainwater for uses such as replenishing aquifers, flushing toilets, and drinking water. For the efficiency of a sponge city, measures to improve the conventional drainage system should be undertaken. Additionally, financing the maintenance of this system and embracing urban forestry is exceedingly important.

Impervious surfaces like concrete do not absorb surface runoff. Rather, they redirect rainwater to drainage systems which are often clogged with debris and solid waste hence causing floods. To correct this issue, permeable surfaces are recommended. Permeable surfaces are characterized by more vegetation than concrete.

Floodplains play a huge role in flood management through water absorption. Therefore, by erecting developments on floodplains, the flood management role can no longer be executed. For this reason, floodplains should be protected from encroachment. Rooftop gardens are essential in controlling floods since they absorb rainwater. They also contribute to the aesthetics of a place and they get rid of toxic nitrogen from rainwater.  

Wetlands naturally store water during heavy rains. They also slow down runoff to streams. It is for this reason that buildings erected on wetlands experience floods during the rainy season. To address this problem, the Nairobi City County should bring down all buildings constructed on wetlands. The City should also prevent the reoccurrence of the same in the future by hiring accountable and transparent professionals.

Another important flood solution is the construction of a rainwater system that is separate from the sewage system. A separate storm water system ensures that the sewage system is not overwhelmed during heavy rains. At the same time, the sewage system should be improved or reconstructed with materials that are non-corrosive and easy to clean. The rainwater system should also be clog-free to allow the proper flow of storm water.

In conclusion, as the rate of urbanization in Nairobi increases, so will the demand for more infrastructure development and housing. Consequently, urban floods will increase. That is to say that the Nairobi floods should be mitigated as soon as possible for the social, physical, and economic well-being of the city.

The writer is a graduate physical/urban planner with a love for writing





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