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Sponge City Kajiado: Urban Recharge on a Shoestring

The town of Kajiado in Kenya faces a number of serious water supply and rainwater runoff problems. All these problems relate directly or indirectly to the way rainwater flows away and no longer infiltrates into the ground. RAIN (a brand of Aidenvironment) is using the Sponge City approach to adapt the urban infrastructure to manage the collection, infiltration, and runoff of rainwater using low-tech solutions.


Figure 1 Location of Kajiado in Kenya

Kajiado faces three main problems.

  • First, storm water flowing from the roofs and roads creates gullies and drags rubbish into the small rivers around the town.
  • Second, without a viable municipal water supply, the demand for water is met by private operators who exploit boreholes in the town or truck water in from sources further away. This water is expensive and not always of good quality, and local sources are being depleted.
  • Third, infiltration from latrine pits causes nitrate to seep into the shallow and deeper groundwater, polluting the groundwater reserves. Several boreholes already show high nitrate concentrations.

 
Figure 2 Gully and dump site

All these challenges relate directly or indirectly to the way in which rain water drains away from town and no longer infiltrates into the ground. Increase of hard surfaces such as roofs and roads contribute to these challenges. The same roofs, roads and compacted grounds create heat traps where wind, dust and sun rule.

How can we reduce the impact of urbanization on groundwater resources and the environment in developing towns of the arid lands such as Kajiado?

At the end of 2016 RAIN received a grant from Via Water to find ways to reduce the impact of urbanization on groundwater resources and the environment in developing towns in arid lands like Kajiado. The solutions focus on augmenting urban infrastructure to make roads, houses, and parks a catchment area from which water can be redirected for infiltration or storage. These solutions seek to:

  • increase recharge of the urban underground water, thereby raising the water table and diluting nitrate pollution;
  • reduce the infiltration of pollutants and improve solid waste management;
  • improve the quality of the urban environment and climate.

Sponge City
The use of urban infrastructure as water harvesting tools is part of an approach called Sponge City. In the Kajiado Sponge City project we aim to make Kajiado an example that can inspire other towns in the arid lands of East Africa. Unlike some other sponge cities in more industrialized countries, the Kajiado program calls for solutions which are low cost, low tech, and low maintenance. As municipal councils in such towns cannot be expected to maintain or invest in costly urban infrastructure, solutions need to be found in diverting gullies, creating flow beds, excavating infiltration gravel pits covered with sand to infiltrate water, and simple weirs to block runoff. It also means planning parks at strategic locations where water remains long enough to infiltrate into the ground. All these things and more will soon be implemented in Sponge City Kajiado. We will keep you informed of progress in future newsletters.

RAIN is a brand of Aidenvironment, setting up programs and projects focusing on rainwater harvesting and 3R techniques.

For more information, please contact Maarten Onneweer.