Estuaries are unique coastal bodies of water where water derived from land meets the sea. In order to preserve estuaries and minimise the effects of human interference in these sensitive areas, an understanding of the hydrodynamics is essential. South Africa has 259 estuaries, of which approximately 70% are temporary open. The aim of the project was to provide data to analyse the effect of different flow scenarios on the frequency, timing and duration of mouth closure for temporary open estuaries. To achieve the project aim, two case studies were undertaken, namely Mhlanga and Mdloti Estuaries. Achieving the terms of reference required monitoring of the mouth state, water level, flow rates and developing an understanding of breaching mechanisms. Observations of the mouth were used to monitor its state and initially photographs were used to monitor the water level within each estuary. During 2003 a continuous water level monitor was developed and placed in each estuary. Velocity readings were taken upstream of the estuaries at discrete time intervals and converted to flow rates using the velocity area method. A photographic survey of the berm at Mhlanga Estuary was used to observe the effect of beach processes on the mouth area. The survey observed the estuary as it shifted from closed through to open, then partially open and finally closed again, providing information on mouth mechanisms. The continuous water level monitoring provides useful information for Mhlanga Estuary in terms of breaching patterns, tidal exchange when in the open state and an indication of the time scales involved in mechanisms which change the mouth state. Similar information for Mdloti Estuary was not available as the estuary did not breach since the installation of the water level monitors, however salinity profiles from 2002 provided qualitative information on the existence of a saline intrusion into the estuary. The relationship between flow and mouth state is complex and relies on other influences such as water level and systems losses. In general estuaries will breach under high flows and remain closed under low flows, however in between these two regimes the estuary mouth state is less predictable based on flow alone. Mhlanga Estuary repeatedly breached at low tide. During the open phase tidal influence was both observed and captured by water level monitors despite the perched nature of the estuary. Closure generally occurred at high tide trapping saline water within the estuary. The two case studies provided a good basis for exploring the affects of different flow conditions on estuaries, with Mdloti Estuary experiencing the effects of the Hazelmere Dam and abstractions, while Mhlanga Estuary has increased flow due to the discharge of treated effluent to the system. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2004.

Climate change and variability have great impact on the hydrological cycle and consequently on the availability of water resources. Variations in temperature and precipitation trends that are occurring are a consequent of the increase in the concentrations of greenhouse gases, which are subsequently affecting the hydrological cycle. This in turn affects water quantity and quality, which is essential for agriculture, domestic and industrial uses. This study, done in Elliot Town and the surrounding areas of Sakhisizwe Municipality in the Eastern Cape Province of South Africa, evaluates how climate change and variability is affecting water availability and its quality in the town. The impact climate change and variability on agricultural production is also assessed. Remote Sensing, Geographic Information Systems (GIS), databases and some statistical packages have been used to collect, analyse and create spatial maps used to derive concrete conclusions. The methods used aided in spatially analysing the changes in temperature and rainfall along the years and make a comparative analysis. The study has shown that the spatial changes in the amount, intensity and frequency of rainfall affects the magnitude and frequency of stream flows; consequently, increasing the intensity of floods and droughts that have been recurring in the last few decades. The municipality is more affected by climate variability than change, and the resultant extreme climate events are affecting the water resources resulting in domestic water cuts, poor water quality and low agriculture productivity. This study recommends the importance of an awareness campaigns on climate change and variability and their effect directed towards the community, especially on novel water harvesting technologies. The study also highlights the importance of a robust early warning system to prepare the community in case of a climate shock, which is an area that needs further research. / Environmental Sciences / M. Sc. (Environmental Science)