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This thesis integrates existing work on surface accretion rates with more recent advances in the understanding of creek hydrodynamics. Concepts drawn from various disciplines are formulated into a revised framework within which marsh sedimentation may be better understood. Channel flux studies that treat the marsh as a 'black box' contribute little to our understanding of marsh functioning, whatever the accuracy of their execution. Marshes are better conceptualised as complex bio-sedimentary systems, characterised not only by an intimate relationship with adjacent tidal waters, but also by numerous internal pathways along which transport of water and materials may take place. Data relating to surface sediments, surface sedimentation, channel and over-marsh hydrodynamics, and suspended sediment composition and settling behaviour have been obtained within a relatively mature back-barrier marsh, 54 ha in area, at Scolt Head Island, on the north Norfolk coast. Tidal range averages 3.2m at neaps and 6.4m at springs. The annual sediment input to the marsh surface is estimated at 675 tonnes, equivalent to a mean accretion rate of approximately 0.26 cm/year. The broad pattern in sedimentation reflects surface topography via its control over inundation frequency. Locally, however, proximity to the creek system as an intermediate sediment source determines the rate and nature of sedimentation. The formation of composite particles via the action of flocculation and organic binding agents determines the depositional behaviour of fine cohesive sediment introduced to the marsh. Particle fall velocities are thereby enhanced, with settling from over-marsh tidal flows being a continuous process and not confined to slack water. Reworking of newly deposited material by deposit feeding gastropods appears to be intense over much of the marsh, and may be an explanation for the paucity of sedimentary structures. The marsh surface acts as a topographic threshold separating markedly different spring and neap creek flow regimes. Morphological development of the creeks is effectively confined to ebb-dominated spring tides, when export of sand occurs. Though the creeks act as effective conduits for material transport, a large proportion of the total spring tidal prism may be exchanged directly over the marsh edge. These results may be viewed in the context of present concern over rising sea levels linked to human-induced global warming. Scenarios for future sea-level change vary widely, though most estimates put the present rate of eustatic rise at approximately 1-2 mm/year. Subsidence along this coast is around 1mm/year. Thus many marshes exist in delicate equilibrium with present relative sea level. A numerical model incorporating quasi-continuous deposition, annual tide data, and eustatic and crustal movements successfully simulates historic marsh sedimentation along the north Norfolk coast and provides an insight into the possible effects of future eustatic changes.

Flood warning systems have been researched and discussed for several decades and there is a high degree of consensus in the literature that the most effective structure for a flood warning system is that of an integrated system. Experience suggests however, that few, if any, operational systems are designed in an integrated way and that few practitioners fully appreciate the benefits of integration. Through an analysis of arrangements in the Thames Basin, this research addresses this issue by identifying the necessary criteria and actions required to introduce an integrated system. The limited number of models that attempt to conceptualise flood warning systems in an integrated way have been critically examined and have found to focus too narrowly on selective integrative criteria. It is concluded that there is a need for a wider and multidimensional perspective. This study rectifies this deficiency by presenting a conceptual model that is derived from a more comprehensive assessment of the most relevant integrative factors. A two-staged process is adopted with an initial identification of a wide range of issues and variables, leading to a more focused set of factors presented under four main headings that are used to structure the substantive chapters of this thesis. These integrative factors can be conceptualised as crosscutting strands running through and drawing together the main components of a flood warning system (detection, forecasting, dissemination and response) that help ensure that these components work together collaboratively towards a common aim. Few of the integrative factors identified in this research were found in operational flood warning practices in England and Wales prior to 1996. A number of improvements were made with the establishment of the Environment Agency as the lead authority in both flood forecasting and flood warning dissemination, but a number of weakness still prevail. Through the use of case studies the plausibility of introducing a fully integrated approach to future arrangements has been tested and found to be both practical and feasible.

Development of the shallow alluvial groundwater of the Hadejia-Jama'are-Yobe River valley flood plain (northern Nigeria) has been taking place with increasing intensity over the past decade. However little has previously been known about the nature of the Yobe River-aquifer interaction, including the recharge mechanisms. This thesis reports on a study of the river-aquifer interaction in the middle section of the basin, centred on a field site near Gashua, Yobe State. Detailed field studies were undertaken over a period of 14-months, which involved geoelectical sounding, drilling and water level monitoring. The results of the field study show that the Yobe basin is underlain by a sand and gravel aquifer, which is covered by an average of 1-3m of clay. The Yobe River is in hydraulic continuity with the adjacent alluvial aquifer and variations in aquifer storativity have been recognised as an important factor in understanding the hydraulic behaviour of the Yobe River-alluvial groundwater system. A confinedunconfined groundwater regime exists within the present site and is an inherent characteristic of the alluvial groundwater system. The recognition of this state enables a conceptual flow model of the system to be developed. A multi-layer, spatially distributed model is proposed, in which transitions between confined and unconfined conditions can be realistically represented. A numerical model needs to be designed with these concepts in mind in order to simulate the system. The research techniques employed in the study are appropriate for the assessment of the Yobe basin system where detailed data is currently not available. The combination of detailed geophysical survey, water level monitoring and conceptual modelling has led to a good understanding of the Yobe River-alluvial aquifer interaction. It is for this reason that the techniques employed in this study can be adapted for investigating the remainder of the basin downstream of the present site.

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