Evaluation of the Streamflow Response to Agricultural Land Expansion in the Thiba River Watershed in Kenya

Abstract

The expansion of agricultural lands in the Thiba River watershed, particularly in the Mwea Irrigation Scheme and other parts of the watershed, has resulted in excessive water abstraction from the Thiba River, thereby reducing its flow and affecting its downstream users. This study aimed to evaluate the potential impacts of the expansion of agricultural lands on the streamflow regime of the Thiba River and its impact on the downstream users by comparing the 2004 and 2014 land uses and simulating the long-term impact using the HEC-GeoHMS and HEC-HMS models. The results showed a considerable decline in the streamflow in the dry months compared to the wet months, with increasing water abstraction trends from 2007 to 2014. The long-term impact assessment showed an average decline in streamflow in the near (2030) and far (2060) future due to land use and population changes with minimal impact from the increasing precipitation. Based on these findings, there is a need for proper water management and adaptation mechanisms to be put in place to maintain the future water supply from the Thiba River. The study's findings could assist policy and decision-makers in making informed water resource management decisions.