Publications
Effect on estuarine fine-sediment transport of intermittent pump discharge at Pagham Harbour, West Sussex, by S. B. Mitchell, B.Sc., M.Sc., Ph.D., C.Eng., M.I.C.E., H. M. Burgess, B.Eng., M.Eng. and D. J. Pope, Ph.D., published March 2004 in Water and Environment Journal (vol. 18, issue 1, article, pp.39-43) View Online
Abstract:Field investigations were undertaken to identify the mechanisms of fine-sediment transport at a landward limit of Pagham Harbour. Which is a semi-enclosed natural harbour in West Sussex, UK. Measurements of water level, velocity, salinity and turbidity were made during three tidal cycles between June and August 2002. Near-bed measurements revealed that, for spring tides, the most significant transport occurs during the flood tide, with smaller turbidity peaks recorded at times of intermittent pumped discharges at low water. Vertical profiling revealed that the timing of these discharges acts as a control on the landward transport of fine sediment by increasing salinity stratification. The resulting graphs show that, while increased near-bed velocity leads to increased turbidity and sediment transport, the degree of vertical salinity gradient is also linked with landward transport of fine sediment. These results help to explain the role of tides and fresh-water flow in controlling the transport of fine sediment in natural harbours, emphasising the importance of taking stratification into account when using 2-D depth-averaged predictive numerical models.
Stratification and fine sediment transport mechanisms in a semi-enclosed tidal lagoon (PaghamHarbour, West Sussex), by S. B. Mitchell, H. M. Burgess and D. J. Pope, published December 2006 in Water and Environment Journal (vol. 20, issue 4, article, pp.248-255) View Online
Abstract:Preliminary analysis of data collected at a macrotidal semi-enclosed lagoon (Pagham Harbour, UK) has revealed useful information about long-term patterns of siltation and some of the related mechanisms. Sediment surface-level measurements made over 2 years at different sites within Pagham Harbour have shown a steady siltation, in common with earlier measurements, which is moderated by seasonal effects due to erosion by locally generated waves. Furthermore, inspection of vertical profiles of salinity and turbidity over individual tidal cycles has revealed that the degree of sediment transport on the flood tide is related to the vertical salinity gradient. Thus, at the Ferry Pool site, which is characterised by episodic pumped discharges from a nearby sewage treatment plant, landward sediment transport is enhanced by the high degree of salinity stratification observed during the flood tide. The mobility of the sediment, and the greater distribution of softer, less well-consolidated sediment deposits, is greater here than at the other significant freshwater inflow at the Salthouse site, where the fresh water flow is instead moderated by a tidal flap gate. Preliminary analyses suggest that the higher the salinity stratification, the greater the landward sediment transport during the flood tide. Such analyses could help inform future policy on the methods of land drainage to macrotidal lagoons, and on the potential for managed realignment at such sites.