Hydrology

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Browsing Hydrology by Author "Rawlins, B.K."

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    Simulation of catchment runoff, erosion and sediment transport using a transient numerical model for Mlalazi catchment
    (University of Zululand, 2019) Rasifudi, Khathutshelo Joshua; Simonis, J.; Rawlins, B.K.
    Catchments and estuaries are fragile systems that are prone to serious degradation from many different anthropogenic impacts. Much research has been conducted on developing an understanding of the fluvial processes in river catchments and in estuary dynamics. Many of the anthropogenic impacts on estuarine systems are generally derived from subjective expert opinion in South Africa. The Mlalazi Estuary is one of the best conserved estuaries in KZN. As a result of the changing state of the marine and fluvial conditions there is a possibility that such changes may trigger management interventions. There is therefore a need to derive reliable flows from the Mlalazi Catchment as it is a driver of sediment deposition and erosion processes which may impact on the opening or closing of the Mlalazi Estuary. The latest Reserve Determination study for Mlalazi Estuary was based on rapid assessment with low confidence (<40%) in simulated monthly streamflow. The study illustrated a need for further detailed assessment of catchment hydrology using appropriate and calibrated models. In an ungauged catchment where there is limited observed data, numerical models are useful tools to derive best estimates of flow, erosion and sediment transport. In this study the HEC-HMS hydrological model was developed, calibrated, validated and applied for simulation of runoff, erosion and sediment transport from the Mlalazi Catchment into the estuary. Calibration and validation was done at delineated sub-catchments with observed flow records. An event based calibration approach and a continuous approach were used in the development of the model. For the event model the initial and constant loss method was used for simulating rainfall loss from the catchment surface, while the Soil Moisture Accounting (SMA) Model was employed for the continuous simulations. The event calibration was based on two selected extreme storm events, namely the Domoina (31 Jan 1984) and Imboa (17 Feb 1984) cyclonic events; and the validation was done on two storm events in February 1985 and September 1987. The calibration and validation for continuous simulations of flows were from 1977-1986 and 1986-1999 respectively. The Nash-Sutcliffe Efficiency (NSE) and overall Root Mean Square Error (RMSE) were used to evaluate the model performance. The continuous flows for the catchment were then simulated from 1950 to 2017 incorporating erosion and sediment transport. The erosion was simulated using the Modified Universal Soil Loss Equation (MUSLE), and the Ackers-White method was chosen for sediment transport potential. The erosion and sediment transport models SIMULATION OF CATCHMENT RUNOFF, EROSION AND SEDIMENT TRANSPORT USING A TRANSIENT NUMERICAL MODEL FOR MLALAZI CATCHMENT v were not calibrated due to limitations of observed data, but parameter values were estimated from other studies available in literature for this region. The simulated sediment yield from the catchment was evaluated by comparison to sediments yield found by other studies in this region. It was concluded that a physically based, numerical simulation model provides a pragmatic method for the derivation of reliable hydrodynamic data and information in catchments with limited observed data like the Mlalazi Catchment. Furthermore, this study allowed a smooth linkage with the study of the Mlalazi Estuary that employed the HEC-RAS model.
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    The variance in the water quality of the lower orange river
    (University of Zululand, 2019) Sekwaila, Kwena Khutjo; Simonis, J.J.; Rawlins, B.K.
    The monitoring and assessment of rivers is important for measuring the status of river ecosystems, water quality and water demand, and can provide early warning for management intervention with regard to water quality and quantity. This can be quite a daunting undertaking for rivers that cross national boundaries such as the Orange River. Concepts such as Integrated Water Resource Management were introduced to enhance the sustainable use and management of such water resources. In addition, transboundary bodies such as the Orange-Senqu River Commission were established between member states in the Southern African region to provide a platform for coordinated water resource management of the river. The DWS has various water quality monitoring programmes throughout the country. The National Chemical Monitoring Programme is the longest running of the national monitoring programmes. While the National Microbiological Monitoring Programme provides data for determining the potential health risks to people related with the potential utilization of pathogenically polluted water resources. This study identified and evaluated the effectiveness of sampling locations by analysing water quality trends from monitoring points in the Lower Orange River located in the Northern Cape. Historical data from the Department of Water and Sanitation‟s Water Management System and National Integrated Water Information System were utilised to illustrate changes in the water quality temporally and spatially. The legislative requirement of water quality in South Africa, according to the South African Water Quality Guidelines, was applied to the data sets. The current water quality network of the Lower Orange is under-utilised. The various sites are not monitored on a consistent basis. A large number of sites have been left inactive and not monitored. Creating a situation where the latest data may not be available for management decisions. The general trend of the river water quality indicates a general increase in the Total Alkalinity in the river. This potentially is the results of years of runoff from irrigation practices into the river. The river also displays high levels of phosphate, nitrate and magnesium at some monitoring points. iv There are large gaps in data, and thus limited information, in terms of water quality of the Lower Orange River. Studies conducted by organisations such as the ORASECOM also indicate a lack of information with regard to Persistent Organic Pollutants, heavy metals and radio nuclides. These potential major pollutants are currently not being given priority compared to other parameters.. Water management authorities and institutions require research that supplies a constant flow of information in order to adequately respond to water quality changes in the river. This study identified gaps between the monitoring and management of the Lower Orange River. In addition, it provides potential mitigation measures that could help ensure the gaps are closed and water quality data is converted into information that can enhance understanding of the water quality in the Lower Orange River. Policy formulation for water quality management in the arid Northern Cape can be made much easier with this information.