Freshwater resource characterization and vulnerability to climatechange of the Shela aquifer in Lamu, Kenya

Abstract

Salinization of coastal groundwater systemscauses a severe deterioration both in amount and quality offresh groundwater resources. To support the sustainableuse and management of fresh groundwater, quantificationand characterization of these coastal resources are impor-tant in view of the population growth anticipated in manyAfrican countries. Analytical methods were used to deter-mine: (1) the shape and volume of the freshwater lens, (2)the elevation of the water table, (3) the depth of thefreshwater/saltwater interface in the Shela aquifer, and (4)the expected change of volume resulting from change ofrecharge and sea level rise driven by climate change. Theresults of the analytical modelling have shown that theaverage hydraulic conductivity is 0.755 m/d, the averagewater table elevation is 2 m above sea level and the aver-age depth of the freshwater/saltwater interface is -80 m.a.s.l. The volume of the aquifer is&1249106m3when discharge from the Shela well field is factored in.Climate change is expected to have an impact on therecharge and ultimately the aquifer’s volume; under theA1b conditions, the volume is expected to increase to1999106m3whereas in the A2 scenario it is expected todecrease to 279106m3. The saltwater intrusion indicatorMfor today’s conditions (0.004) decreases to 0.5Min theA1b scenario by 2100 whilst it increases to 24.9Min theA2 scenario for the same time period, indicating anextremely higher vulnerability to saltwater intrusion in thelatter scenario. A simple linear correlation with theexpected population growth of 1.25 million people by 2050shows the aquifer failing as a water source by 2033