River mouths are characterised by a conflict between marine and fluvial processes, in which the planimetry of the mouth is dependent on the relative contribution of wave, tide and current, which may be manifested in spit and barrier accumulation forms, and the often opposing force of river discharge. Analysis of historical geomorphological evidence shows that the Donmouth has a history of constant change. In 1975-74, in order to assess the relative importance of fluvial and marine factors in explaining this change, monthly and seasonal tacheometric and sediment sampling was undertaken on the spit-bar which extends north across the mouth, and on the updrift beach. The dynamics of both form and material were measured. Hydro™ . graphic surveys of the estuary, nearshore and offshore morphology and material, and measurements of waves and currents were also conducted in the field. Field'data was analysed in_the laboratory and-by computer to produce quantitative results which serve to complement the qualitative description,. Results of the various analyses serve to illustrate a model example of rlver-mouth variability and dynamic equilibrium. The Donmouth Is located in a stretch of soft coastline characterised by a strong south to north wave and current energy continuum, which is reflected in northerly increases in elements of beach, nearshore and offshore form, process and material, out of the wave shadow provided by the rock headland at the southern extremity of th© bay. a s part of this continuum, the Donmouth is largely characterised by a marine-formed spit-bar, whose dimensions are dependent on the level of river and estuarine discharge. Models of spit-bar variability and of river-mouth planimetry were thus facilitated and are presented.

Thesis (Ph. D.)--Louisiana State University, 1979. / Vita. Includes bibliographical references (leaves 87-92).