This study was concerned with the submerged bottom type of river intake, which consists, essentially, of a filter located in the river bed, through which water can be pumped. This type of intake has been used recently, for example, in salmon rivers, to minimise disruption of fish movement. The problem of assessing the change in bed shear stress over the intake was studied with a view to estimating the depth of the scour hole, which was known to be a feature associated with abstraction. The literature on local scour in alluvial channels was studied, several different types of scour being covered by the survey. Although most of the methods described were limited in application to a certain type of scour, some general principles were observed. In particular, it became clear that it was important to obtain an adequate description of the modification of the flow field giving rise to the scour. Several different turbulence models were assessed before a decision was made on the approach to be adopted to the problem. The more complex models were considered unsuitable, mainly because excessive attention to detail in the flow field would be unwarranted when other aspects of the problem, such as the suction force on the grains and the relationship between grain movement and boundary shear stress, were not known with sufficient accuracy. In addition, there was some uncertainty in the modifications to such models that would be required for their application to the intake problem. The extended law of the wall for suction flows was rejected because it is valid only for suction velocities up to about 1% of the external flow velocity, whereas the suction velocity in the intake flows studied ranged from 2% to 10% of the mean flume velocity. Solutions based on the mean flow momentum equation were studied, and a model was developed which was based on the hypothesis that the increase in shear stress at the bed was related directly to the momentum given up by the abstracted fluid at the bed. This model gave significantly improved predictions compared with a previous model, in respect of both the magnitude and pattern of shear stress distribution in the suction zone. It also had an advantage over the earlier model in that the results did not depend significantly on the assumption of a hydrostatic, or any other, pressure distribution in the main flow. Measurements of the modification of the velocity field associated with abstraction were made over a suction zone in a wind tunnel. The velocity profiles at a number of different points along the suction zone were measured using a hot-wire anemometer and these provided confirmation that the profiles assumed for the purposes of calculation gave an adequate description of the flow. Shear stress measurements over a model intake in a laboratory flume were made by observing the combinations of suction and flume flow which induced threshold conditions for sand grains placed on an impermeable disc in the suction zone, whose threshold shear stress in uniform flow was known. The measurements of shear stress using this method gave results which were between five and ten times lower than the predicted values, although they were comparable to estimates of shear stress based on the near-bottom velocities measured in the wind tunnel. It was deduced that the absence of suction at the disc itself was responsible for this large difference, since tests with dye showed that the disc did not interfere noticeably with the main flow. Measurements were also made of the bed profile over the model intake in the flume at various stages in the development of the scour hole, and the bed shear stress estimated from these measurements. These estimates showed a reasonable correlation with the predictions of the new mathematical model, but it was clear that there was a need for a better understanding, especially with regard to the interpretation of the experimental data. This study has provided a means of estimating the boundary shear stress associated with abstraction, and the resulting grain dislodgement rate and scour. These estimates are approximate in nature, but ways of obtaining improved predictions have been indicated, and these should provide a sound basis for an extension of this work to the study of three-dimensional scour which is important in the application of the results to intakes in practice.

A programme of field sampling was undertaken to quantify annual organic carbon fluxes at a range of sites on the River Dee and River Don in NE Scotland. The annual fluxes of both DOC and POC in the R. Dee and R. Don were found to increase cumulatively with distance down the river system. In headwater and tributary catchments of the R. Dee, annual DOC fluxes were positively related to the coverage of peat in the catchment area. This work as supplemented by a desk study in which organic carbon exports in 1993 were calculated for 85 large British rivers, using archive information. The resulting estimates, along with data on the soil carbon content of 17 river catchments were used to develop a predictive model of British riverine DOC fluxes. Calculated and predicted DOC fluxes and estimates of POC export based on suspended solids data, were combined to produce estimates of the annual British riverine organic carbon export during 1993. The 'non-storm' flux of DOC in British rivers in tidal waters during 1993 was estimated at 0.69 Mt +/- 0.28 Mt; the corresponding POC flux estimate was 0.2 Mt. A direct method for measuring dissolved CO2 in river and lake waters was developed. Preliminary studies of rivers in NE Scotland and lakes in Northern Wisconsin, USA, suggested that lakes may act as conduits for CO 2 transport, particularly in catchments containing substantial wetland. In conclusion, soil carbon content appears to be a useful integrative measurement for predicting annual DOC fluxes in British rivers. The establishment of a link between soil carbon stores and riverine fluxes, should help to improve future modelling of the carbon cycle. These findings suggests that rivers (and lakes) may regulate increases in soil carbon pools induced by climate change.

No description available.

No description available.

In 1993 concerns were expressed by English Nature that Devon's three largest sand dune systems Braunton Burrows, Northam Burrows and Dawlish Warren were drying out to the detriment of the dune habitat flora and fauna. Research was therefore required to understand how these systems functioned hydrologically, to determine whether they were drying out and if so to recommend sustainable management options aimed at reinstating former water levels, or preventing any further lowering of the water tables. At Braunton water table elevations have been monitored on a monthly basis by the Nature Conservancy, the Nature Conservancy Council and English Nature since 1972. These data were invaluable in describing the spatial and temporal hydrological characteristics and functioning of the groundwater system. Braunton Burrows was the main study site of the research. At both Northam and Dawlish, at the start of the fieldwork programme a dipwell monitoring network was installed and water table elevations were recorded weekly. Hydrological characteristics of each dune system were related to temporal variability in effective precipitation, the tide, the underlying geology and sediment properties. The groundwater system at Braunton was mounded, with effective inputs accumulating over an impermeable basal layer close to mean sea level. The system was very sensitive to seasonal variability in effective precipitation. At the centre of the groundwater mound, during the winter months, the elevation of the water table was 10 in above OD. The groundwater mound was asymmetric, with the highest water table elevations occurring along the eastern margin of the system. The transitional zone from dune sands to marshland, of a lower permeability, was restricting the inland lateral drainage regime and was controlling both the shape and elevation of the water table. At Northam the groundwater system was also mounded and again the shape and elevation of the water table were dependent upon effective precipitation. Unfortunately the monitoring network at Dawlish proved insufficient to describe either the shape or elevation of the groundwater table. Within the smaller systems of Northam and Dawlish variable sediment properties lead to intra-site variability in annual cyclical water table fluctuations. A prominent trend in the long-term water table data for Braunton Burrows was the general overall decline in the elevation of the water table from 1983 to mid 1992. With precipitation as the primary source of groundwater recharge, consecutive years with below average effective precipitation (1983-1992) was undoubtedly the primary cause, but was exacerbated by the drainage improvement works carried out on West Boundary Drain in 1983. Scrub growth, artificial drainage of the golf course and marine erosion were also possibly influencing the groundwater drainage regime. At Northam and Dawlish, without historical data it was not possible to determine if the systems were drying out, however factors influencing annual cyclical water table elevations were identified. Again climate was the key variable controlling the long-term elevation of the water table and undoubtedly the dry spell between 1983 and 1992 would have had repercussions on the elevation of the water table within these two systems. At Northam the drainage ditch network and reduced tidal inundation were the other main factors influencing groundwater levels. At Dawlish the golf course pump drainage system and scrub encroachment were effectively reducing annual groundwater recharge. At Braunton a numerical groundwater flow model was used as a predictive management tool, to assist in the recommendation of sustainable water level management options. A range of commercial groundwater flow models were reviewed and Visual MODFLOW, incorporating the original United States Geological Survey's MODFLOW code, with a fully integrated pre and post processor, was selected as the most suitable model for the Braunton scenario. The modelling exercise had three objectives; to test whether a commercial model such as Visual MODFLOW could be applied successfully to simulate the hydrology of Braunton Burrows; to gain further detail on the hydrological functioning of the system and ultimately if the model was calibrated to test a set of management scenarios to predict the hydro-ecological consequences of introducing new management practices into the system. Having identified the most probable factors influencing water table elevations within each dune system, sustainable hydrological management options were recommended with the aim of raising water levels, or preventing any further decline in water table elevations. The management options afforded nature conservation the highest priority, but also took into consideration the long-term requirements of all the other land user groups.A t Braunton when formulating the managemenrt ecommendationst he modelling predictions were also taken into consideration. Potential areas for future research were also identified. Water level monitoring should continue at all three sites, so that the longer-term impact of any water level management strategies implemented as a result of this research can be evaluated. Also at both Northam and Dawlish a more detailed analysis of the geology and sediment properties would be invaluable in providing a more comprehensive hydrological description of the functioning of the groundwater systems. The Braunton groundwater model could be developed further, addressing and overcoming problems encountered in this study and evaluating a wider range of water level management scenarios. As a result of this research far more is understood about the hydrological functioning of Devon's three largest dune systems and the recommendation of sustainable remedial/restorative water level management options will help to ensure that these ecologically diverse habitats are conserved for future generations. This research has also provided both the applied and theoretical framework to address water resource management problems within small and large scale dune systems around the shores of Great Britain.

Natural radioelements and inert gases in solution in groundwaters have been applied to problems of groundwater flow and age measurement. The 4He content of groundwaters generally increases with age and in the Bunter Sandstone, Nottinghamshire, the 4He contents of groundwaters have been linearly related to 14C ages. In the Lincolnshire Limestone, the He contents of the groundwaters have been used to indicate mixing of recharge water and interstitial water. In the other study areas, 4He and 40Ar in groundwaters have been used as qualitative indicators of age. The 4He contents of core samples have been related to the 4 He contents of the interstitial water and the formation depth. 4He diffusion in confined and non--confined sedimentary structures has been discussed. The amounts of non-radiogenic inert gases dissolved in groundwaters have been used to estimate groundwater recharge temperatures. In the Bunter Sandstone, these have been related to palaeoclimatic history by calibrating with the 14C ages. Estimated recharge temperatures have also been related to seasonal recharge, changes in the altitude of recharge and to variations in the hydrogen and oxygen isotopic ratios. Variation of the 222Rn contents of groundwaters has been used as an indicator of aquifer variability. The relative importance of intergranular and fissure flow and the variation in efficiency of 222Rn release into groundwaters has been investigated. The fraction of 222Rn released from rocks has been determined and the mechanisms by which 222Rn is released from sandstone, limestone and granite rock fragments has been discussed. Variability of the 226Ra contents of groundwaters has been explained in terms of the relative importance of the recoil and etch mechanisms of solution and the solubility of 226Ra salts in groundwaters.

The mechanism of Rn solution in groundwaters has been studied in both laboratory simulations and in field situations. The effect of sporadic and seasonal changes in rainfall patterns on the Rn contents of perennial springs in the Mendip Hills has been investigated. The separate contributions of surface streams, soil zone residence and percolation within the rock formation have been identified. The relative importance of fissure or conduit and percolation flow in the aquifer have been shown to determine the nature of the response of Rn content to rainfall patterns. An examination of the Rn contents of air in limestone caverns has established that intergranular diffusion of Rn from below the rock surface is the primary reason for Rn release into the air space. Rn transport and release from stream inflows is relatively unimportant. Experimental determinations of the Rn diffusion coefficient in rock sections have shown that such intergranular diffusion is much more significant than intragranular diffusion. Laboratory studies of Rn release from fragmented rock samples have been used to determine the efficiency of radon release for different rock types. These studies have also confirmed that intergranular diffusion is an important process by which groundwaters acquire high Rn contents. The Ra content of geothermal groundwaters from Iceland have been determined. The Ra and U contents of calcite deposits from various depths within these geothermal systems are discussed in relation to changes in the Ra geochemistry. Rn contents have also been determined for groundwaters from the Berkshire Chalk and are shown to be dependent upon the extent to which porewater mixing has occurred.

No description available.

No description available.

No description available.