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Environmental problems associated with the use of water are inherently complex, involving the interaction of several different systems. Further, there is often limited data on the interaction, because of its location between disciplines. In order to study these problems in a quantitative, policy relevant way, a numerical model is required that integrates the different systems and is tailored to contain the processes important to the interaction. A numerical water resource system model is developed to study the problems associated with the interaction between agriculture and water. The model integrates an econometric model of farmer behaviour with a dynamic model of water flow and solute transport. The Argolid valley in Greece represents an area where severe environmental problems have arisen as a result of the overexploitation of groundwater for agriculture. When applied to the Argolid valley the water resource system model reproduces the evolution of the environmental problems that have arisen. It is then demonstrated that the model can be used to investigate some future scenarios and policy options related to the environmental problems that have developed. The main contribution of this research is to demonstrate that a properly designed numerical model that reproduces the dynamic interaction between human behaviour and the physical environment can enable the exploration of the evolution of environmental problems despite a lack of calibration data. Having achieved this the model can then be used in a policy relevant way to investigate the implications from a range of different, possible policy options.

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Flood inundation phenomena typically occur over reach lengths of 5- 30 km and incorporate a number of complex flow mechanisms. These include a momentum transfer between the main channel and floodplain and turbulent mixing caused by the delivery of water to the floodplain from the channela nd its subsequenrte turn. However, currently available one dimensional schemes applicable at scales appropriate to floodplain inundation processes cannot effectively simulate such processes. This is due to both an incomplete description of the flow physics and a failure to treat floodplain areas in realistic fashion. More complex two and three dimensional models, which have these capabilities, have only been applied over very short reach lengths (c. 0.5 -2 km) and rarely to compound meandering channels. This thesis reports on the further development of a generalized two dimensional, finite element code (RMA-2) to meet this research need. This is achieved via a series of modifications to the numerical model and to the physical representation by finite elements that enable river channel/floodplain flow at the long reach scale to be effectively simulated. Evaluationo f the enhancedR MA-2 schemef ollows a three stages trategy. Firstly, the assumptions underlying the scheme are examined to identify possible inconsistencies. Secondly, tests are undertaken to assess whether the specified physical model has been correctly transferred into computer code. This is achieved via sensitivity analysis, examination of numerical stability issues and investigation of model response to abnormal parameterization. Thirdly, model predictions of flow field information are compared to observed field data in the context of an application of the enhanced model to an 11 km reach of the River Culm, Devon, UK. Results from this evaluation process indicate that the enhanced RMA-2 model is capable of simulating main channel/floodplain momentum transfer and the two dimensionale ffects associatedw ith compoundm eanderingc hannelsa t this scale. Model simulations compare favourably to field data, both for specific cross sections and over the entire mesh. Finally, extension of this core modelling capability is begun via the development of two model application scenarios. These demonstrate the likely utility of the enhanceds chemef or the assessmenotf flood risk and the investigationo f sediment depositionp rocessesin floodplain systems.

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In the course of my duties as a hydrologist with a British regional water authority, I am frequently required to derive riverflow statistics for catchments for which there is little or no measured flow data. Whilst there are many existing methods by which flows may be estimated, my experience has been that the majority of these approaches are unreliable. This thesis describes the development of a suite of alternative, user orientated, high and low flow estimation techniques for application in ungauged catchments. As the derived methods require the cross reference between a large number of figures, these have grouped together as a separate volume, together with appendicies which include all analysed data. However, second copies of selected figures and all summary tables have been included within the main text as an aid to explanation.

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No description available.