Rock catchment design system: Nzambani rock case study

Water is life. Unfortunately this prerequisite commodity is unevenly distributed across the globe
as some areas receive it in abundance while others get less than inadequate. In the arid and semi
arid regions of the world, rainwater harvesting was necessitated to buffer the acute shortages and
scarcity. Rock catchments have been adopted aggressively particularly in Kitui where suitable
rocks are available.
This case study was stationed at Kyuluni area in Kitui at the Nzambani rock where a rock
catchment system was sized. The most suitable rock surface area was found to be 3036.44m² and
the rainfall intensity during the wet season amounted to 309.7mm in a year. From these two
components, the available run off was calculated. The effects of slope of the catchment area and
consumption during the wet season was analyzed to get the available volume of runoff to be
stored for use in the drought period that last through June to October. The maximum run off
generated was 651.69m³.
The runoff was compared to the present and the ultimate future demand in a 2km² cordon. The

current number of households was ascertained at 15 while the ultimate number of households
was perceived at 23 considering the growth rate in Kitui. The present sufficient water demand
was found to be 434.9m³ while the ultimate sufficient demand was anticipated to be 666.9m³.
The study found that a tank size of 450m³ was the most suitable to cater for the future demand of
about 19 households with consideration to economic costs and at the same time avoid wastage
and overflow in the tank under the conditions presented by the area.


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