Bulk Water Supply: Water Resources Assessment and Numerical Aquifer Modelling
GWS has frequently been commissioned to determine the environmentally sustainable safe yield from local and regional aquifers. The common approach in such cases is to map out the aquifer in a 3-dimensional way by making an inventory and evaluating all readily available data followed by hydrogeological and geophysical surveys. The next phase usually encompasses detailed aquifer testing to determine optimum yields of exploration holes. This process usually ends with well field designs and construction supervision. Sometimes, more challenging studies are undertaken such as the determination of sustainable pumping regimes for high yielding well fields in coastal aquifers prone to salt water or high yielding well fields drawing water from a river-fed aquifer. Good examples of such projects are the Tiwi Coastal Aquifer study for the water supply of the Kenya South Coast (water demand 15,000 m3/day) and the Sabaki Aquifer study for the supply of Mombasa City, Malindi Town, and the area in between (water demand 70,000 m3/day). Another example is Nakuru Town (water demand 15,000 m3/day). The surface and groundwater studies for the water supply of a titanium mine in Kwale (maximum water demand 28,000 m3/day, ongoing) and for the water supply of Dodoma City in Tanzania (water demand 70,000 m3/day) are also good examples. The common denominator of such bulk water supply studies is the economic necessity to exploit the available surface and groundwater resources in full while avoiding overexploitation of the ecosystem. Some of these major projects have been described in more detail in the Appendices.