V.O. Odongo

The Effects of Groundwater and Surface Water Use on Total Water Availability and Implications for Water Management: The Case of Lake Naivasha, Kenya

This study discusses the effects of water abstractions from two alternative sources on the available water volume around Lake Naivasha, Kenya: the lake itself and a connected aquifer. An estimation of the water abstraction pattern for the period 1999–2010 is made and its effect on the available water volume in Lake Naivasha and its connected aquifer is evaluated using a simple water balance modeling approach. This study shows that accurate estimates of annual volume changes of Lake Naivasha can be made using a simple monthly water balance approach that takes into account the exchange of water between the lake and its connected aquifer. The amount of water that is used for irrigation in the area around Lake Naivasha has a substantial adverse effect on the availability of water. Simulation results of our simple water balance model suggests that abstractions from groundwater affect the lake volume less than direct abstractions from the lake. Groundwater volumes, in contrast, are much more affected by groundwater abstractions and therefore lead to much lower groundwater levels. Moreover, when groundwater is used instead of surface water, evaporation losses from the lake are potentially higher due to a larger lake surface area. If that would be the case then the overall water availability in the area is more strongly affected by the abstraction of groundwater than by the abstraction of surface water. Therefore water managers should be cautious when using lake levels as the only indicator of water availability for restricting water abstractions.

Supporting IWRM through spatial integrated assessment in the Lake Naivasha basin, Kenya

This study describes the mismatch between required knowledge and efforts by scientists and stakeholders in the Lake Naivasha basin, Kenya. In the basin, integrated water resources management (IWRM) suffers from the absence of critically relevant knowledge. This study further presents a spatial integrated assessment framework for supporting IWRM in the basin. This framework resulted from an ongoing debate between stakeholders and scientists studying the basins issues. It builds on jointly identified indicators for sustainable governance, and their interdependency, and knowledge gaps. For IWRM in the basin this is a first important step towards a more structured debate on the implementation of IWRM.