Groundwater potential in tertiary and triassic sediments in Kidiani area, Kwale district, Kenya

Abstract

This thesis describes the results of a hydrogeological project carried out in Kidiani Area of Kwale District, about 60 kilometres south-west of Mornbasa. With a view to evaluate the groundwater potential in Kidiani Area, Kwale District, geophysical resistivity method was applied. Here, the vertical electrical sounding (VES) was done using the Schlumberger electrode configuration. The VES results show that potable water zones occur in both Magarini sands and Mazeras sandstones. Iterative, non-automatic inversion of VES data, coupled with borehole information, resolved with some confidence the conductive j non-conductive water interfaces and revealed some correspondence between the lithostratigraphic units and resistivity values. Maps of resistivity and transverse resistance values agree reasonably with the general hydrogeological conditions in the area. Within the Mazeras sandstones the results suggest that groundwater is strongly associated with the presence of structural features in the subsurface where seasonal recharge is likely. Correlations have been established between the conductive zone resistivity and the water salinity and to a lesser extent between the transverse resistance and the potential area(s) for groundwater prospecting. From the available Recovery test data of the wells in the area, Jacob's straight line method of analysis depicted the nature and the well characteristics mainly transmissivity, (T) and specific capacity,(QjS) with sufficient confidence. Determination of some aquifer limitations and to a lesser extent, relative well efficiency were also made. Further, groundwater analysis was carried out to determine its quality and possible uses. Generally, it is observed that groundwater in the Tertiary Magarini and Kilindini sands has lower salinity than the water in the Triassic Mazeras sandstones. From the observations made in this study, it can be concluded that the Cenozoic Magarini and Kilindini sands have ahigher groundwater potential than the Tertiary Mazeras sandstones. Moreover, these observations could be used to assist in the exploration and evaluation of groundwater resources in new target areas in the Coast Province where lithostratigraphical and hydrogeological information is very limited.