Abstract
D.Ing. (Civil Engineering)
The Lepelle River Basin (LRB) formally known as the Olifants River Catchment situated in the north-eastern part of south Africa is a very important catchment in the country owing to its huge coal reserves. The development of water resources has been critical to the evolution of agriculture and industry in the Catchment. Water supplies, on the other hand, are currently under tremendous stress, while water demands continue to rise. Water scarcity is one of the greatest roadblocks to growth in the catchment; both the mining and agricultural industries are generating at sub-optimal levels due to limited water supply. This study was carried out to possible investigate the effects of future climate variations in the LRB for extreme flow conditions such as drought (low flow conditions) and flooding (high flow conditions). Climate change continues to escalate the magnitude of the insecurity of water resources across the LRB. This is largely due to lack of habitat resilience in the African continent. As a semi-arid nation, South Africa ranks between 37 and 39 driest countries of the world. Against this backdrop the Water Evaluation and Planning (WEAP) systems model was employed to evaluate the availability of water into the future of the LRB especially during extreme flow conditions (very Low and very high flows). Hence this study investigates the effects of future climate variations in the LRB under extreme flow conditions. A historic scenario with a base line of 1980 was used to ascertain the changes over time of water availability (1980 – 2019). Two sets of plausible scenarios are then used to model the future hydrology (2020 – 2099) of the LRB. The WEAP model was used to set up the hydrology of the LRB with all the water demands in the area. The model was calibrated and validated against observed data to verify the ability of the model to simulate the internal hydrological processes of the catchment. For this study, 17 major dams together with 51 water demand sites within the catchment which were grouped into six sectors namely Urban, Rural, Irrigation, Mining, Industrial and Power generation were modeled. The difference in results between the historic and future water availability gives us an idea of the effects of climate change on the water resources of the catchment. The results for future streamflow of the LRB generated from WEAP were further used as input into a Drought Indices Calculator DRINC for estimating drought. DrinC predicted drier conditions as we approach the 22nd century with more frequent droughts than in the past interspaced by random flooding events. However, the water demands in the LRB promises to be met if the inter basin transfers schemes from other catchments into the LRB remains in place. This situation, however, cannot be guaranteed. Trend analysis was carried out to determine if there is an obvious trend in the pattern of extreme events (drought and floods). The results indicated no significant pattern in the extreme events but rather assists in predicting the timing and magnitude of future drought and flood events in the catchment under the two Representative v Concentration Pathways (RCPs). Further flooding events were investigated using Arc Hydro, HEC-Geo HMS, HEC-HMS and HECRAS.