A six- year water balance for Mbagathi sub-catchment
Increasing water demands with limited supplies is a growing concern for agencies charged with its provision while observing equity and fairness. This study set out to balance water supplies to the demands in Mbagathi sub-catchment. Groundwater recharge was estimated using the sub-catchment soil water balance method while surface water supplies were estimated using Mbagathi river discharge from stream-flow gauge stations 3AA04, 3AA06 and 3BA29. Survey data collected in 2015 using snowballing approach was used to quantify water demands. Surface water balance rose from -1.54 in 2010 to 0.47 million m3 in 2015 compared to groundwater that reduced from 22.66 to -0.38 million m3. Groundwater balance reduced due to a rise in resource demand, inefficient use and limited exploitation of wastewater in the study area. Surface water balance increased due to pollution of resource making it unsafe for use. Unsustainable water availability amidst over-reliance on groundwater and dominance in domestic and agricultural uses was observed in Mbagathi sub-catchment necessitating drastic management measures of the resource. These include adopting water use efficient practices such as water harnessing, de-siltation of reservoirs and water reuse to manage rising water demands and explore alternative water sources in the study area to ease pressure on existent supplies and prevent negative water balances in future.
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