IWRA Proceedings

Like most arid and semi-arid regions in sub-Saharan Africa, northwestern Kenya is characterized by insufficient surface water resources and depends almost entirely on groundwater for domestic, irrigation, and drinking water supplies. The occurrence and distribution of fresh groundwater in drylands are limited and are constantly threatened by climate variability and human-induced risks. In particular, Lodwar municipality is one of the fastest growing towns in sub-Saharan Africa. Its population in 2019 was 82,970, indicating a near-double population growth of 42.5 % since 2009. It is the largest town in northwestern Kenya and the headquarters
of Turkana County. The town abstracts groundwater from boreholes and handpumps located along the Turkwel River, the only perennial river in the county originating in the Mt. Elgon highlands in western Kenya. Although shallow alluvial aquifers can provide locally important groundwater sources, their comparatively small size and dependence on decadal precipitation recharge rates limit their sustainable use. By 2018, no scientific information was available for comprehensive evaluation of the arid urban alluvial aquifer. The Lodwar Alluvial Aquifer System (LAAS) investigation was based on multi-disciplinary field studies to assess the quantity, quality,
and potential uses for available groundwater. We used major ion hydrochemistry and stable isotopic compositions of rainfall, surface water and groundwater to evaluate intersystem linkages, recharge sources in different aquifer types and propose management policies for groundwater use. The results revealed that the LAAS comprises three varied sub-systems with depths ranging between 5 to > 100 m deep with cumulative aquifer storage of 1.3 billion cubic meters (BCM) of renewable and potable freshwater. The water quality is suitable for drinking and irrigation purposes, defining the observed settlement patterns along the riparian zones of
the Turkwel River and dominant small-scale irrigation. Human health is threatened by increasing nitrate levels in all the aquifer sub-systems during the wet season, though the quality is still within national and WHO standards. This scenario is fuelled by the lack of a sewerage network in Lodwar town and dependence on on-site sanitation infrastructure, which sometimes is not well constructed. Groundwater not linked to Turkwel river, the Turkana Grit Aquifer Systems, host highly mineralized water with EC levels between 3000 – 8000 μS/cm; unsuitable for drinking and irrigation purposes. Groundwater resources in northwestern Kenya are directly linked to livelihoods and peoples’ health. Lack of adequate control, intensive abstraction can lead to aquifer overexploitation and subsequent water table lowering. Besides, poor sanitation and
unregulated human activities in the river catchment can lead to permanent aquifer contamination. The study provides evidence for policy development and groundwater protection and management in northwestern Kenya and other arid regions.