Browsing by Author "Taylor, Valerie."
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Item The hydrological basis for the protection of water resources to meet environmental and societal requirements.(2006) Taylor, Valerie.; Jewitt, Graham Paul Wyndham.; Schulze, Roland Edgar.In common with other natural systems, aquatic ecosystems provide a wealth of economically valuable services and long-term benefits to society. However, growing human populations, coupled with increased aspirations for improved quality of life, have lead to intense pressure on the world's finite freshwater resources. Frequently, particularly in developing countries, there are both perceived and genuine incompatibilities between ecological and societal needs for freshwater. Environmental Flow Assessment (EFA) is essentially a tool for water resources management and its ultimate goal should be the integration of ecological and societal systems. While other ecological components (i.e. biological and geomorphological) are equally important to EFA, this thesis investigates the role of the hydrological cycle and the hydrological regime in providing the ecosystem goods and services upon which society depends. Ecological and societal systems operate at different temporal, spatial and organisational scales and hydronomic zoning or sub-zoning is proposed as an appropriate water resources management technique for matching these different scales. A major component of this thesis is a review of the South African water resources management framework and, in particular, the role of the Reserve (comprising a basic human right to survival water as well as an ecological right of the aquatic resource to maintain ecological functioning) in facilitating ecologically sustainable water resources management. South African water resources management is in the early stages of water allocation reform and the Department of Water Affairs and Forestry has stated that "the water allocation process must allow for the sustainable use of water resources and must promote the efficient and non-wasteful use of water". Thus, new ways of approaching the compromise between ecological and societal needs for freshwater water are required. This thesis argues that this requires that the focus of freshwater ecosystems be extended beyond the aquatic resource, so that societal activities on the catchment are linked to the protection of instream flows. Streamflow variability plays a major role in structuring the habitat templates that sustain aquatic and riparian ecological functioning and has been associated with increased biodiversity. Biodiversity and societal well-being are interlinked. However, there is a need in EFA for knowledge of the most influential components of the streamflow regime in order that stakeholders may anticipate any change in ecosystem goods and services as a result of their disruption to the hydrological cycle. The identification of high information hydrological indicators for characterising highly variable streamflow regimes is useful to water resources management, particularly where thresholds of streamflow regime characteristics have ecological relevance. Several researchers have revisited the choice of hydrological indices in order to ascertain whether some indices explain more of the hydrological variability in different aspects of streamflow regimes than others. However, most of the research relating to hydrological indices has focused primarily on regions with temperate climates. In this thesis multivariate analysis is applied to a relatively large dataset of readily computed ecologically relevant hydrological indices (including the Indicators of Hydrological Alteration and the South African Desktop Reserve Model indices) extracted from long-term records of daily flows at 83 sites across South Africa. Principal Component Analysis is applied in order to highlight general patterns of intercorrelation, or redundancy, among the indices and to identify a minimum subset of hydrological indices which explain the majority of the variation among the indices of different components of the streamflow regimes found in South Africa. The results indicate the value of including several of the IHA indices in EFAs for South African rivers. Statistical analysis is meaningful only when calculated for a sufficiently long hydrological record, and in this thesis the length of record necessary to obtain consistent hydrological indices, with minimal influence of climatic variation, is investigated. The results provide a guide to the length of record required for analysis of the high information hydrological indices representing the main components of the streamflow regime, for different streamflow types. An ecosystem-based approach which recognises the hydrological connectivity of the catchment landscape in linking aquatic and terrestrial systems is proposed as a framework for ecologically sustainable water resources management. While this framework is intended to be generic, its potential for application in the South African Water Allocation Reform is illustrated with a case study for the Mkomazi Catchment in KwaZulu-Natal. Hydronomic sub-zoning, based on the way in which societal activities disrupt the natural hydrological processes, both off-stream and instream, is applied to assess the incompatibilities between societal and ecological freshwater needs. Reference hydrological, or pre-development, conditions in the Mkomazi Catchment are simulated using the ACRU agrohydrological model. Management targets, based on the statistical analysis of pre-development streamflow regimes, are defined to assess the degree of hydrological alteration in the high information hydrological indices of the Mkomazi Catchment as a result of different societal activities. Hydrological alteration from predevelopment conditions is assessed using the Range of Variability Approach. The results indicate that the proposed framework is useful to the formulation of stakeholder-based catchment management plans. Applying hydrological records (either observed or simulated) as an ecological resource is highly appropriate for assessing the variability that ecosystems need to maintain the biodiversity, ecological functioning and resilience that people and society desire.Item Hydrological modelling applications for water resources management in the Mkomazi Catchment.(2001) Taylor, Valerie.; Schulze, Roland Edgar.Predictions that water shortages will constrain economic growth in South Africa by 2025 have led to increased concerns among water resource managers that there is a need for comprehensive water management strategies. To this extent the new South African Water Act requires that water resource allocation be approached in a more equitable and conservative way than in the past in order to sustain water resources for catchment development. This includes protection of the water resource base by the setting aside of a health Reserve for basic human needs and for the ecological functioning of rivers. At a time when water resource management is shifting from the practice of large dam construction to reconciling water demand with water supply in more holistic strategies, the Mkomazi Catchment in KwaZulu-Natal provides an opportunity to investigate some of the major issues that dominate contemporary water resource management. Presently (2001), there are no impoundments on the Mkomazi River and the catchment is generally underdeveloped. These factors have provided the impetus for the Department of Water Affairs and Forestry's proposed inter-basin transfer scheme to use the surplus flow in the Mkomazi Catchment to augment the water resources of the neighbouring Mgeni system. Impact-of-Iand-use and development scenario studies, using the ACRU agrohydrological modelling system, were performed to simulate the impacts of (a) baseline land cover, (b) present land use, (c) the first phase of the Mkomazi-Mgeni Transfer Scheme and (d) potential climate change on the hydrological dynamics of the Mkomazi Catchment. The results indicate that the change from baseline land cover conditions to present land use conditions has little impact on the annual water resources of the Mkomazi River. This is especially so in the upper catchment where there is little anthropogenic development and from where the planned inter-basin transfer will be made from the proposed Smithfield Dam. Although the impacts of commercial forestry and irrigation in the middle and lower catchment impose local stress on streamflow generation, they do not detract substantially from the main downstream flows. Evaluation of the impacts of the proposed Smithfield Dam on annual streamflow generation revealed that there is more than sufficient water in the upper Mkomazi Catchment to sustain the inter-basin transfer under present climatic conditions. However, under potential climate change the median annual Mkomazi streamflows at the estuary could be reduced by 46% if the dam was constructed, compared with a 22% reduction under present climatic conditions. The impacts of catchment development on the seasonal low flows within the Mkomazi Catchment indicated that those areas which are already heavily utilised by afforestation and, particularly, by irrigated land use are unlikely to be able to support any further large scale commercial agricultural development, even under present climatic conditions. Water management strategies for the Mgeni system will impact on potential water allocation within the Mkomazi Catchment. The results of the impacts studies were used to assess the water demand of the major water-use sectors and the availability of streamflows for further allocation was assessed. Present total annual water demands of Mkomazi streamflows is minimal. Even allowing for the environmental demand in the Mkomazi Catchment, as identified by the Building Block Methodology during an instream flow requirements workshop, as well as the first phase of the inter-basin transfer, there would be surpluses of 66%, 43%, 42% and 45% of streamflows, respectively, at the four instream flow requirement sites on the Mkomazi River. The results of the Mkomazi instream flow requirements workshop were revisited to assess the achievability of the recommended flows within the ACRU generated daily time series of streamflows for each of the scenarios simulated, at the each of the four instream flow requirement sites on the Mkomazi River. The results confirmed the need to ascertain the Mkomazi River's natural flow variability, and to assess how much alteration is likely under development of the Mkomazi Catchment. The Indicators of Hydrologic Alteration and Range of Variability Approach methodologies were used to determine which components of the streamflow regime would be most impacted by the inter-basin transfer. Hypothetical, yet realistic, upper and lower management target thresholds were applied to determine the range of variation experienced by the streamflow regime of the Mkomazi, under both pre- and post-dam construction conditions, and to evaluate a preliminary assessment of the characteristics of the streamflow regime required to meet environmental sustainability. The issues raised by potentially conflicting water uses within catchments in South Africa have indicated that any approach to address the increasing complexity of water resource problems, and the management thereof, requires effective hydrological modelling.