Author(s): Kuria Kiringu; Gerrit Basson; Eddie Bosman; Jeanine Vonkeman

Linked Author(s): Kuria Kiringu, Gerrit Basson

Keywords: Sediment yield, SHETRAN modelling, Climate change, Land use change and Reservoir sedimentation

Abstract: High sedimentation rates at Thwake Dam poses a threat to the dam’s design life span. The SHETRAN hydrological model was utilised to estimate the long-term sediment loads. Three sets of scenarios were considered; observed rainfall + the European Space Agency (ESA) land-use changes for (a) the year 2000, for (b) the year 2016 and for (c) the predicted year 2100 (applying the land change modeller) . The sediment yield was estimated at 1725 t/km2.a (17.62 Mt/a), 1713 t/km2.a (17.60 Mt/a), and 1564 t/km2.a (16.08 Mt/a), for the years 2000, 2016 and 2100 land-use changes, respectively. This showed that the predicted future land-use change sediment yield decreases slightly by 10% over time. The Delta Change Approach methodology was utilized to determine the RCP8.5 CORDEX-Africa downscaling experiment climate change signals and with the calibrated SHETRAN model, two scenarios were considered: (d) the current rainfall increased by 2100 climate change signal + the ESA year 2000, and (e) land change modeller’s year 2100 land-use changes. The year 2100 climate change only sediment yield was estimated at 3199 t/km2.a (32.87 Mt/a) and the year 2100 land use and climate change sediment yield at 3250 t/km2.a (33.4 Mt/a). This showed that the predicted future sediment yield could increase by as much as 47% from the current estimates. Apart from catchment land care, the following engineering measures were investigated: sediment bypass tunnels, check dams, dam raising, drainage gully at the heel of the dam wall and dredging of sediment. Based on this pre-feasibility study, land care combined with check dams are the proposed mitigation measures.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022SS2817

Year: 2022