Browsing by Author "Chrystal, Robynne Angela Lawrie."

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Anthropogenic impacts and biophysical interactions in Lake St Lucia.
(2013) Chrystal, Robynne Angela Lawrie.; Stretch, Derek Dewey.
The St Lucia estuarine lake system in South Africa is part of a UN- ESCO World Heritage site and a Ramsar wetland of international importance. Like many estuarine systems worldwide St Lucia has experienced signi cant anthropogenic impacts over the past century including catchment land use changes, water diversions/abstractions and inlet manipulation. In addition, the system has recently su ered losses in species diversity and abundance following unprecedented hy- persaline conditions and desiccation. Questions regarding its sustain- ability have motivated a reevaluation of management decisions made in the past and of options for the future. To understand the func- tioning of the system, it is necessary to analyse it holistically in terms of the physical processes and their interaction with the biology. This study focusses on aspects of the biophysical interactions in the estu- arine complex, and aims to provide new knowledge to underpin the development of improved models for predicting the response of the system to anthropogenic interventions. A model for the water and salt budgets was used to investigate what if scenarios in terms of past anthropogenic interventions, in particular the e ects of diverting the Mfolozi River from St Lucia. Furthermore, the risks of hypersalinity and desiccation were assessed for each sce- nario. Integrating these modeled scenarios with observed biological responses to physicochemical changes suggested that large long-term changes in the ecological structure can be expected in the di erent management scenarios. To validate this, the ecosystem response to changing environmental responses was quantitatively assessed using ecological network analysis. Long-term simulations show that the separation of the Mfolozi and St Lucia mouths had a signi cant impact on the functioning of the St Lucia system. The Mfolozi plays a pivotal role in maintaining a more stable mouth state regime and provides a vital source of freshwater during dry conditions. The con guration of the Mfolozi/St Lucia inlet plays a key role in the physico-chemical environment of the system and in uences the system's susceptibility to desiccation and hypersaline conditions. Ecosystem indices revealed that the water level, salinity and mouth state have a signi cant impact on species abundance and diversity as well as the ecological structure and functioning of the system. In addition, ecosystem indices show that the system recovers rapidly during favourable conditions. The arti cial separation of the St Lucia and Mfolozi inlets underpins the most signi cant impacts on the water and salt budget of the lake and its reversal is key to the sustainability of the system.
The use of small scale hydroelectric power in South Africa, hydro and economic potential for rural electrification.
(2012) Reddy, Devan.; Chrystal, Robynne Angela Lawrie.; Stretch, Derek Dewey.
Small hydro generation refers to generating capacity of less than 10 MW with the most common being Run-of-River. In South Africa, the level of rural electrification is approximately 50 percent with most of the energy needs being met with biomass fuels. The purpose of this study was to investigate the hydropotential regions that were identified by Eskom and the Department of Minerals and Energy in 2002 and determine sites for small scale development for rural electrification purposes. Technical and feasible analyses were carried out in order to assess the applicability of this kind of energy generating system. The aim of this study was to consider the Free Basic Electrification policy and Solar Home Systems to assess the electrical demand of rural households and possible funding transfer scheme respectively. Furthermore, to formulate an appropriate methodology that can be used given the available data and resources currently available in South Africa. In total, six sites were identified and analysed in this paper, namely: (1) Berg River at gauge G1H013, (2) Mzimvubu River at gauge T3H008, (3) Orange River at gauge D1H003, (4) Mlambonja River at gauge V1H041, (5) Thukela River at gauge V1H002 and (6) Mkomazi River at gauge U1H005 which are in the Eastern Cape, Western Cape and KwaZulu-Natal Provinces. Flow gauge data were analysed in order to develop monthly mean Flow Duration Curves which were used to determine the design flow, power generation (through Power Duration Curve construction) and renewable energy potentially produced from each scheme. Costing functions were utilised in order to determine the initial capital cost of the system which was used to assess the project’s feasibility. In order to predict potential power output of the schemes, the streamflow and hydraulic head of the six rivers were assessed. The potential renewable energy production ranged from about 240 to 6060 MWh/year. Through this energy production, it was found between 165 and 10100 houses could be electrified depending on the electrical allowance provided. This significantly exceeds existing housing numbers. Costing bands ranged from 3 – 7 R/kWh which was high but within reason based on the community income and the transfer of the Solar Home Systems pricing policy. The results of this study provide a good foundation for future work in the estimation of hydropower potential in South Africa and will hopefully be a stepping stone to better estimation of both technical and exploitable hydropower potential for South Africa.