This chapter presents the results of a study on the influence of streamflow variability on salinity, total dissolved solids (TDS) and conductivity in a semi-arid Tiva River Basin in Kenya. Measurements of salinity, TDS, conductivity and river discharges were undertaken in sampling stations by applying standard hydrologic methods. The study shows that there is a significant relationship between the variability of streamflow and the variability of salinity, conductivity and TDS in the river. The high salt concentrations were a result of high evapotranspiration and seepage of subterranean water from bank storage and groundwater aquifers. Inter-sub-basin variations in the levels of salinity were attributed to differences in land uses, lengths and sizes of the sub-basins. Sustainable irrigation and land use practices in the semi arid Tiva River Basin requires construction of water reservoirs for control of salinity levels in the river.
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Seasonal rivers in arid and semi arid lands (ASALs) of Africa are important sources of water to communities and their livestock. However, despite the important role played by seasonal rivers in such lands, few studies have been undertaken to unravel their hydrologic and water quality characteristics (Kitheka, 2013 & 2014). There is thus scanty of data and information on river discharges and material (including nutrient, sediment and salt) fluxes in seasonal rivers of Sahelian Africa. The contribution of African seasonal rivers in terms of global nutrient and material fluxes is therefore little understood, since most of the hydrological studies have focused on perennial river systems (Ohowa et al., 1997; Busulwa and Bailey, 2004; Waziri and Ogugbuaja, 2010; Waziri and Ogugbuaja, 2012; Elmoustafa, 2013; Kitheka, 2013 & 2014). Seasonal rivers in semi arid lands are unique in that they usually flow for relatively short period during rainy season. Data and information on their hydrology are required to advice on the water resources and agricultural development programmes. This is becoming critical as a result of climate change and also due to current programmes that are aimed at opening up arid and semi arid lands for development. Seasonal rivers could be the only reliable source of water that can be used to develop ASALs.
Most of the studies on seasonal rivers in Kenya have focused on water pollution, soil erosion and nutrient fluxes (see Kithia, 1997; Ohowa et al., 1997). Some studies on Kenya have shown that some seasonal rivers at the coastal basin are characterized by high nutrients loads in rainy season as compared to dry season (Ohowa et al., 1997). Recent studies on Kenya’s largest river-Tana have demonstrated the effects of modification of streamflow and sediment load as a result of damming of the river in the Upper Tana Basin (Kitheka, 2013 & 2014).. However, despite the impact of damming, Tana river still receives substantial sediment load from seasonal streams such Tiva river that drains into the lower Tana Basin (Figure 1a). To our knowledge, no studies have been undertaken on salt fluxes in rivers of Kenya. However, past studies on salinity conducted elsewhere have shown that the main driving forces acting in shaping seasonal variation of salinity include low natural drainage density of the catchment, which limits the salt loads induced by the natural runoff processes, and the runoff in the catchment area which promote dissolved salt dilution during the high-flow period (cf. Kaabata et al., 2012).