Effect on estuarine fine sediment transport of intermittent pump discharge at Pagham Harbour, West Sussex

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.