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A general survey was carried out on the sediments of seventeen lakes, ranging from oligotrophic to eutrophic, in the English Lake District. Several variables not directly concerned with the population of bacteria were measured to provide background information. Estimates of the total population of bacteria and of the population of filamentous bacteria were made using direct counts with acridine orange and fluorescein di-acetate, and counts by an MPN technique. The counts with acridine orange showed an upward trend with increasing degree of enrichment of the lakes, particularly at the eutrophic end of the spectrum. The distribution pattern obtained with the fluorochrome fluorescein di-acetate was different with an apparent upward trend in the intermediate lakes. The viable counts of the bacterial population in the sediments did not agree with the ranking of the lakes according to published information from the Freshwater Biological Association, although a slight upward trend was observed in the distribution of the viable filamentous bacteria. The preliminary survey led to the selection of three lakes representing the oligrotrophic, mesotrophic and eutrophic states in which a more detailed investigation on the population of filamentous bacteria was made. The profundal and littoral zones of the three lakes were investigated particularly in relation to the different groups of filamentous bacteria and their vertical distribution in the sediments. The groups of filamentous bacteria were described based on morphological and cytochemical tests. A tentative key for identification of filamentous bacteria was devised.

An evaluation has been carried out of the groundwater system in Bahrain. It has involved the collection of water samples from all the water bearing formations to study the quality of the groundwater. Each water sample was tested physically, chemically, and bacteriologically. Additionally, the five day biochemical oxygen demand test and hydrogen sulphide were detected. The period of the actual sampling and testing extended from mid-1990 to the beginning of 1992. The results obtained have been compared to the results of an earlier study conducted between 1978 and 1979. The investigation has also involved a statistical analysis of the variations in the sub-surface water table level in each hydrogeologic formation. The piezometric levels have been collected from monitoring boreholes/ standpipes. The levels obtained extended from the beginning of 1980 when the earliest recording started up to the end of 1991. Bahrain abstracts its fresh water from five aquifers which in descending order are the Sanad, the Alat, the Khobar, the Rus, and the Umm-Er-Radhuma Aquifers. The quality of the groundwater appears to be deteriorating. The excessive groundwater abstraction has caused the encroachment of the sea into all the sub-surface waters. As the waters become saline, they are expected to become unsuitable for human consumption and for irrigation. The deeper aquifers are believed to consist of high values of the hydrogen sulphide because the deeper geological formations contain oil rich in sulphur. land spring water is expected not to be safe bacteriologically because it is exposed to the atmosphere unlike the other boreholes in the various aquifers.The water table levels have been changing in each aquifer. The groundwater levels in the Sanad Aquifer, which is the shallowest geological formation, are expected to rise in the future in areas where the natural drainage is obstructed. This is related to the sea coast reclamation area. The rise is expected to reduce inland depending on the application of surface irrigation as well as the possible leakages from the services systems. About two kilometres south from the original shore, around Buddayya Road, the Sanad Aquifer's water table has been shown to be falling. This fall is expected to be due to overpumping from the groundwater system. Apart from the Sanad Aquifer, the piezometric levels of the underlying aquifers are expected to fall with time. Once again the fall is due to excessive groundwater abstraction. The study concludes by re-presenting the causes for the water table rise in the near-surface Sanad Aquifer and discusses the possible geotechnical consequences. It further produces some possible solutions to control the rise of the water table level.

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Most investigations of river meanders have concentrated on classical bends that have a helical flow structure through the pool, which is carried through into the entrance of the next bend. However, it is known that flow separation can occur at the outer bank before the bend apex or at the inner bank after the apex and that this results in the breakdown of the classical flow model. Although some of the controls and the implications of flow separation are now known, the frequency of occurrence, threedimensional (3-D) flow structure, sediment dynamics, controls on separation presence, and full geomorphological implications are poorly understood. This thesis uses a combination of fieldwork and 3-D numerical flow modelling (computational fluid dynamics, CFD) to investigate meander bends where flow separation and recirculation zones are present. An initial reconnaissance survey of over 600 bends revealed that flow separation is common, being present in approximately 50% of bends. The survey also identified high bend angles of tum and the high angles of flow impingement onto the outer bank as important controls on the presence of separation. Investigations in a 22 bend sub-set indicated that expansions in channel width, breaks in bank-line curvature and the angle of inflow, as governed by upstream planform, were important in generating flow separation. Detailed fieldwork combined with validated and verified time-averaged CFD modelling in three bends with separation zones enabled identification and examination of the 3-D flow fields. The simulations reveal that the flow structure in bends with separation differs considerably from the classical flow model, with the helical motion found in classical bends being very intense in the bend entrance but dissipating at or just after the bend apex. The turbulent flow structures produced by the shear layer between the downstream and recirculating flow are also investigated in the field bends and attempts at modelling transient flow structures with large eddy simulation (LES) in a simple open channel flow expansion are detailed. The geomorphological, sedimentological, and ecological implications of both the time-averaged and the transient flow structures within the bends are examined and discussed.

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A water balance model is derived for Sitka spruce in which transpiration is estimated with a diffusion equation, and interception is predicted with the Gash model. A model drought stress index is defined. It assumes that transpiration and growth are maintained at maximum rates until the predicted soil moisture deficit equals 80% of the available water in the root zone. The model has been tested at Kirkhill forest, near Aberdeen, and at Monaughty forest, near Elgin. The drought stress index is validated by field investigations into the effects of drought on tree water status and growth at the Kirkhill podsol P60 site. At the Kirkhill podsol P49 site, the model accounts for 86% of the variation in measured stand annual volume increment (discounting suppressed trees). The model only accounts for 19-35% of the year to year variation in the measured growth of 15 trees at the Monaughty podsol P29 site. The poorer fit of the model at Monaughty is ascribed to periodic thinnings and lower quality growth data. Growth data for two Kirkhill peaty gleys (P57 and P59) demonstrates that drought stress is an unlikely occurrence on such sites. Model predictions of drought stress and evaporative demand are given for several locations across Scotland. It is shown that drought stress is rare in regions such as the West coast and Southern Uplands; in contrast to the East coast, rainfall is high and evaporation low. The model is generalised so that the effects of drought can be assessed simply as a function of annual rainfall and available water. On the basis of the limited number of sites investigated in this study, it is tentatively concluded that, given moderate available water (100-200 mm), reasonable yield classes (16-20) can be expected even when annual rainfall is as low as 700-800 mm.