There is currently worldwide interest in the effect of human activity on tile global environment, especially the effect of greenhouse gases and land-use change on the global climate, and models are being developed to study both global change and the local effects of global change. The research reported here (funded by CNPq-Brazil) involves the development of GRASP:Groundwater Recharge modelling Approach with a Scaling up Procedure. GRASP has been integrated into the UP (Upscaled Physically-based) macromodel, developed under the UK NERC TIGER programme, which is designed for studying the effects of climate and land-use change on the availability and quality of water resources. The UP macromodel will be coupled to the UK Meteorological. Office's Unified (weather and climate) model to create a state-of-the-art coupled atmospheric/hydrological model. Several important requirements for the design of new large-scale hydrological models are identified in a wide ranging review on GCMs; (General Circulation Models) and physically -based hydrological modelling, and these requirements have been applied in the development of GRASP(and UP). The main requirements are a physical basis, proper treatment of spatial variability, and simplicity. Using the concept of partial analysis, two point-scale models, SM (Soil Moisture content approach) and TF (Transfer Function approach), are developed for recharge, both based on the one-dimensional Richards' equation. SM is a simple two-parameter model relating recharge to water storage in the unsaturated zone, and several unsuccessful attempts are made to link its parameters to physical propcrties. TF is a transfer function model, and is parameterised using the matric potential and unsaturated hydraulic conductivity functions using a new approach developed especially for GRASP. Both SM and TF are verified against numerical solutions of Richards' equation.

An analysis of a number of flood routing methods has been carried out in this study. These methods are namely, the Muskingum-Cunge Method, the Variable Parameter Diffusion Method, the State Variable Kinematic Wave Model, and the state variable modelling of nonlinear Muskingum Model. The Muskingum-Cunge and Variable Parameter Diffusion Methods are recommended for use on British Rivers by the Natural Environment Research Council flood studies report, 1975.In using numerical flood routing model, it is very important to calculate the model parameters. For instance storage routing models require a suitable form of storage-discharge relationship. Past flow records were used for the above calculation. The state Variable Kinematic Wave Model has been applied for routing the flood hydrograph through river reaches. The stage and discharge are computed by a kinematic wave routing technique using the state variable approach in which the one-dimensional differential equations of unsteady flow are solved by state and output equations of the state variable model. The nonlinear Muskingum equation has been solved using the state variable modelling technique. Two parameter estimation techniques namely, Hooke-Jeeves and linear regression, are employed for the calibration of the nonlinear Muskingum model parameters (a, x, and m).The applicability of the flood routing model computer programs to different flood events of different seasons for reaches of both the Rivers Wear and Tees is demonstrated. Discriptions of the geology and hydrological data for reaches of both the Rivers Wear and Tees are given in this study. The computed and observed hydrographs of flood routing models used in this study are compared.

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The purpose of the study was to undertake a quantitative assessment of the proportions of river sediment derived from the various rock types within the catchment.b) to determine the rate of removal of sediment from the catchment. The former purpose involved the determination of the mineralogy of source rocks, soils, alluvium and sediment by X.R.D. and heavy mineral analysis. The data indicate that each source rock has a characteristic mineralogy, but that this is not sufficiently variable for a quantitative assessment of proportions of sediment from each source rock to be determined. Certain conclusions, however, are drawn from the data, including a tentative formation, by sorting on a basis of specific gravity, of heavy mineral assemblage zones in channel sediment, that are probably indicative of areas of aggradation and degradation. To determine the rate of sediment loss from the catchment, the dissolved load, the suspended load and thebed load were investigated. The dissolved load includes Ca2+ and HCO3 formed from the solution of Chalk, anderosion rates of CaCO3 have been estimated at approximately 39.8 tonnes/km. 2/year. Suspended sediment concentrations were determined for samples collected from a variety of stations during a variety of flow conditions. An estimated 2,182 tonnes of suspended sediment was lost from the catchment in 1972 , of which 1,720 tonnes was non-organic. The data indicate that the frequency and duration of storm events is a major controlling factor for suspended sediment concentration. Pates of bed load movement were determined using fluorescent sand tracers for two stretches of the Pother and a relationship between grain size, river discharge and sediment loss is presented for each. Modifications of techniques and methodology for use of fluorescent tracers are suggested and the data indicate the probability of aggradation of sizes of medium sand and larger between the two experimental stretches.

This thesis investigates the inter-relationship between hydrological and water quality variations with reference to backwaters and dead zones in rivers. The examination of a series of controlled reservoir releases to an upland channel in Wales showed "in-channel" dead zones were important solute source and storage areas. Physico-chemical data have been presented to show the influence of main channel flow and quality variations on the hydrochemistry of a range of seven backwaters within the Trent basin. The hydrological regime of the mainstream seasonally modified backwater quality. The degree of main-flow influence declined with decreasing hydrological connectivity of the backwater environments with the mainstream. Furthermore other hydrological, biological and biogeochemical factors influenced backwater physico-chemistry. A generalised typology of permanent floodplain water bodies in the R. Trent catchment based upon water chemistry was established. An applied study examined the effect of reservoir cleaning/emptying operations and flood events on backwater hydrochemistry on the French Upper River Rhone. The simultaneous occurrence of decreasing mainstream discharge with the passage of the sediment laden release wave reduced its impact on backwater environments. Anthropogenic influences on riverine systems as a result of intensification of agriculture and urbanisation (e.g. nitrate pollution and river regulation) have influenced the hydrological and physico-chemical functioning of fluvial hydrosystems. In view of rising nitrate levels in many British rivers, trends within the Trent basin have been investigated. Rates of increase in concentration of 0.06 mg.l-1 N yr-1 were typical of rural catchments, whilst rates of up to 0.20 mg.l-1 N yr-1 were recorded in urbanised tributaries. Furthermore the impact of rising nitrate levels in the Trent catchment and river regulation on backwater hydrochemistry and ecology have been examined.

Investigations were initially carried out to characterize the materials present in shape, mineralogical and chemical composition, and particle size distribution. A micro-electrophoresis apparatus was constructed to determine the electrokinetic parameters of the colliery waste-water. The origin of the surface charge which forms on minerals immersed in water is important in flocculation. The nature of the charges on the fines were determined to be both positive and negative. This could be due to the coating of the particles by the addition of the froth flotation reagent used. The electrophoretic mobilities of the particles were measured at the various pH values and at different depths within the electrophoretic cells. These values of the electrophoretic mobilities were used to calculate the values of the zeta potential by the application of Smoluchowski's equation. The iso-electric point (IEP) and the zero point of charge (ZPC) were also investigated and found to coincide at all the different levels of depth within the electrophoretic cell. Finally the colliery waste-water was clarified successfully by flocculating it using the polyacrylamide solution.

The thesis examines the theoretical bases for determining optimal pollution levels in the Trent River Basin, demonstrates that neither the organization of a so-called "market in pollution rights" nor the construction of marginal effluent treatment cost and marginal damage functions is a practical means of finding those levels, and proposes ways for using existing data and the Trent Research Programme river model to determine "roughly optimal" pollution levels.