ASSESSMENT OF THE VIABILITY OF ARTIFICIAL GROUNDWATER RECHARGE IN CORAL AQUIFERS FROM ROOF HARVESTED RAINFALL IN KILIFI TOWN, KENYA

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Date
2021-06-08
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Pwani University
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Artificial recharge of groundwater (AGR) has been used in many countries in the world, with different degrees of success, as well as from different sources of water. In Kenya artificial recharge is a novel idea whose methods of implementation and outcomes have not been explored.The study makes an assessment of the viability of carrying out artificial groundwater recharge in coral aquifers from rainfall harvested from roofs.The lack of data has made it necessary to use several aquifer characterization methods to corroborate the estimation of hydraulic conductivity for the study area. These included petrophysical methods, geophysical inversion of vertical electrical sounding data and two recharge experiments. An unconfined aquifer is inferred from the correlation of water rest levels with elevations from Google earth with the implication that the recovery efficiency/recharge viability can be expressed as a function of permeability, rainfall characteristics, surface area of the harvesting roof/hard surface, Hydraulic gradient and zone of aeration where present.Rainfall was used as the source of water for recharge. In order to understand the study area’s rainfall frequency and intensity, derived satellite rainfall, TRMM3B42v7, data-sets was obtained and validated against two rainfall gauges in Kilifi Plantation and Pwani University of the study area. Validation of the rainfall data allowed for the evaluation of rainfall characteristics relevant to the recharge, at a sub-daily temporal scale. This was necessary in determining the viability for artificial groundwater recharge.viThe challenges due to the lack of data with adequate quality and quantity were addressed by the use of open source data and software.The results of the assessments showed that rainfall runoff from roofs can be used for groundwater artificial recharge in the unconfined coral aquifers of Kilifi, with improvement in the quality of groundwater.The improvement in quality and quantity of water is deemed possible due to the aquifers unconfinement and available zone of aeration together with a low hydraulic gradient. The latter allows a longer residence period of groundwater in the aquifer.An evaluation of Kenya’s current legislation that relates to groundwater recharge has offered insights to its shortcomings compared to legislation in other countries, where groundwater artificial recharge is practiced both as a management strategy and for water supply.
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