Spatial and temporal scales of the morphodynamic evolution within the Studland complex.

Abstract

This research has analysed the large sandy beach at Studland Peninsula over a range of spatial and temporal scales, recording a range of geomorphic features and the processes by which they evolve. The aim was to understand better the morphodynamic evolution of the coastal system over different temporal and spatial scales and identify the extent of changes operating along the beach system. The research has sought to quantify shoreline change from the historical archive by providing an interpretation of the evolutionary sequence of the Studland system over the last 500 years. The linkage between the ebb tidal delta and shoreline progradation has been reviewed. In addition,the temporal variability of the beach system between 2001 and 2004 has been examined. These objectives have been combined to produce a nested hierarchy of spatial and temporal change in the Studland system in order to re-evaluate already existing conceptual models of sediment transportand process. Historic change within the system has been undertaken by a review of historic maps, charts and aerial photographs. Ground Penetration Radar was used to determine the subsurface stratigraphy, providing an indicator of the extent of onlapping and offlapping sand sheets and an interpretation of the morphostratigraphy. Swath bathymetry was used to examine contemporary seabed change within Studland Bay. Regular beach profiles provided datafora time series analysis to be applied to determine temporaland spatial beach behaviour. This study has contributed to furthering the understanding of beach systems by providing a comprehensive overview of beach behaviour on a variety of levels, from the littoral cell to a morphological feature. The study has progressed the understanding of beach sensitivity, and the interplay between ebb tidal deltas and beaches.The results reveal that the Studland Beach system operates as a nested hierarchy of scales, responding to a range of timescales from the historical to the annual. Morphological changes operate at high and low frequencies. The historical trend is for foreshore progradationin the north and erosion in the south. The pattern of variability revealed the importance of sediment feed from the ebb tidal delta to the beach,confirmingthe Poole Harbour entrance is a major contributor to foreshore change. The decadal trends illustrate an accumulation of short-term trends with on and off shore sediment feed via the ebbtidal delta; beach change is muted or hidden by more dynamic frequency variations. Conceptual models were developed to understand geographical relationships between form, process and scale, thus illustrating the relationships between controlling variables, temporal and spatial beach form variability and the system's hierarchy. Profile variability revealed several distinct patterns of spatial and temporal change, enabling discrete sets of profiles to be grouped together to illustrate the complicated relationship caused by geographical and spatial profile variation. Wider beaches with greater profile variability signified stability and accumulation. Scarcity of morphologicalfeatures reflected greater susceptibility to erosion. Furthermore,the study allowed morphological variability to be mapped out, thus providing a complete understanding of the relationships between form and process, at a level of scales never undertaken before.The models have revealed a compartmentalised hierarchical sediment system related to the survivability of beach features; morphological variability and beach stability,linking the components of the system with the whole of the Bournemouth Bay littoral cell.