Use Of Urban Surface Runoff For Groundwater Recharge In Nairobi City.
Abstract
Surface run-off harvesting systems of collect and store rain-water from rooftops, lawns and street
runoffs for later use. While the catchment experiences high run-off in the dry season severe
water shortage is experienced. Water crisis keeps looming because of the intense pressure on
water resources. Some wells in the upper aquifer within the depth up to 120m below ground
level have dried up, indicating depletion.
The objectives of the study were to establish the contribution of groundwater recharge by surface
runoff in the mitigation of urban floods in Nairobi. Desk studies were undertaken. Using ArcGIS
10.3 and Boolean Logic function, the parameters of land use cover, slope, geology and vadose
zone thickness were analysed, and feasible parameter layer maps were generated. Integration of
the feasible parameter layer maps using the Boolean logic function resulted in a feasible area
map. The identified feasible areas for groundwater recharge provided for guidelines for planned
recharge for the city. To determine urban flood characteristics, Landsat images were used to
generate land use cover using ArcGIS. The rate of change in land use was determined. The
rational method was used to estimate the run-off potential thus the proportion to be harvested.
Due to non-uniform piezometric level ranging between 30.5m and 120m below ground level, it
was evident that the aquifer is multi-layered. 22.57% of the area was found feasible for the
planned recharge of the aquifer. For the analysed land use, the available runoff potential
proportion was found to be 47.26%. The runoff potential is fundamental as all this water can be
channelled to the artificial groundwater recharge. The run-off thus showed the potential of
augmenting groundwater in the dry season. The greatest most remarkable outcome will be a
reduced rate of aquifer depletion. This is achievable by the implementation of stormwater
harvesting to increase groundwater recharge. The study showed a co-benefit of flood mitigation.
Publisher
University of Nairobi
Subject
Use Of Urban Surface RunoffRights
Attribution-NonCommercial-NoDerivs 3.0 United StatesUsage Rights
http://creativecommons.org/licenses/by-nc-nd/3.0/us/Collections
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