Browsing by Author "Barnardt, Georg Frederik"

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    Modelling the future impacts of climate change on sediment yield for a semi-arid catchment in South Africa using SHETRAN
    (Stellenbosch : Stellenbosch University, 2021-03) Barnardt, Georg Frederik; Basson, G. R.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: Sedimentation (caused by soil erosion and high sediment yields) has become a major problem in South Africa, especially in semi-arid regions like the Karoo, where water scarcity and reduction of reservoir storage capacity can cause social and environmental concerns. The uncertainties regarding the impact climate change may have on the hydrological cycle, and the effect on catchment response increase these concerns. This thesis's main objective was to evaluate the possible future impacts of climate change on sediment yield by incorporating predicted future climate data and a physically-based hydrological and sediment yield model, SHETRAN. From a literature study, background information regarding soil and vegetation properties, soil erosion, sediment yield, physically-based models (focussing on the SHETRAN model), climate change, and climate models were obtained. The Nqweba Dam catchment (3651 km2), located in the semi-arid region of the Eastern Cape of South Africa, was identified for the analysis. All the information and data required to execute a SHETRAN simulation were obtained, which include: Topography; soil distribution and -characteristics; land cover distribution and vegetation properties; streamflow data; and reservoir survey data. The reservoir survey data was used to determine the historical bed sediment densities and average sediment yield for numerous historical periods in the catchment. The SHETRAN model was calibrated against observed streamflow and sediment data for current catchment and climate conditions. The calibration parameters were verified, and high sediment yield areas were identified. Future climate data projected by eleven climate models for two possible future emission scenarios were used to determine climate change signals for numerous future periods. The climate change signals were applied to the current climate data to represent possible future climate conditions. It was determined that climate change would cause an increase in average rainfall and evaporation in the study area. The possibility of vegetation change was evaluated and the calibrated SHETRAN model was implemented for different future scenarios. It was found that climate change will increase sediment yield in relation to the baseline period for the Nqweba Dam catchment. However, the predicted sediment yield is still lower than some historical observations. During the early 1900s, sediment yields higher than 400 t/km2/a have been recorded, while the future predictions range between 90 and 200 t/km2/a. The current sediment yield for the Nqweba Dam is 57 t/km2/a. The historical catchment characteristics were evaluated. It was determined that poor farm management and overgrazing during the early 1900s had a more significant influence on catchment response and the increase in sediment yield than climate change. Improved farm practices and the construction of numerous farm dams that act as sediment traps significantly impacted the decline in historical sediment yields. It was suggested that improved farm management must be maintained. In high sediment yield areas, farmers must be educated on the impact of overgrazing and poor farm management on erosion and the downstream effect. Recommendations for the methodology that can be adopted to model climate change and suggestions for future research were given.