Abstract:
Kaptagat Forest, the main source of Ellegerini River which feeds the Ellegerini Dam
and Two Rivers Dam, is under threat of extinction due to human activity. The Two
Rivers Dam catchment that has over the years been a source of water in Uasin Gishu
County is slowly depleting and urgent measures are required to restore it. Activities
including commercial logging, charcoal burning and firewood harvesting have exerted
a lot of pressure on the catchment, posing a great threat to the livelihoods of the
people of Eldoret town who depend on the reservoirs for water supply. The main
objective of this study was to develop SWAT and WEAP models for the sustainable
management of water resources in the Two Rivers Dam catchment. The specific
objectives were to set up and apply SWAT model to generate simulated river flows
draining to the Two Rivers and Ellegerini Reservoirs as an input to the WEAP model,
to determine the impact of land use change on the hydrological function of the Two
Rivers Dam catchment, to set up, calibrate and validate a WEAP model for the Two
Rivers Dam catchment and to apply the WEAP model in analyses of various
management and infrastructural development scenarios to enhance water storage in
the Two Rivers and Ellegerini Reservoirs. The goodness of fit SWAT model
statistical evaluation indices attained during the calibration period of 1980 -1984 were
R
2 = 0.854, NSE = 0.822 and Bias = 0.392. Additionally, for the validation period of
1985 -1989 the R2 = 0.786, NSE = 0.815 and Bias = 0.381. The modeled results
indicate that the land use change resulted in decreased baseflow and increased surface
runoff hence the high fluctuations of water levels in the Two Rivers and Ellegerini
reservoirs. The WEAP model results for actual and simulated water demand in
calibration period of 2019, the R2 = 0.88 while during the validation period in the year
2020, the R2 = 0.85. The results of model simulation indicated that the management
option that had the most impact on all the scenarios was the reduction of unaccounted
for water while the one with the least impact was increased water use efficiency. It
was concluded that the models were able to simulate the observed conditions
reasonably well and can therefore be used to effectively manage water resources and
assist the relevant stakeholders in decision-making. The study recommended that
forested areas need to be properly conserved in order to restore the hydrological
function of the catchment.
