Pagham beach and harbour entrance
Pagham Harbour is a natural tidal inlet just east of Selsey in West Sussex. Its narrow entrance, which cuts through a shingle barrier beach, occasionally shifted position until it was stabilised by a training wall in the 1960s. The harbour, and the beaches either side of its entrance are designated as a Special Protection Area (SPA), both because of the plants and animals found there and because it is a rare example of an active geomorphological processes. In recognition of this, and because there are few assets at risk, the 2009 Coastal Defence Strategy for this frontage recommended a policy of adaptive management of the defences against coastal erosion and flooding.
In contrast, east of its entrance, there has been a gradual increase in the number and value of houses forming Pagham Beach Estate since the late 1940s. The present coastal defence strategy here is to “hold the line”, i.e. to maintain the present standard of coastal defence. The risk of flooding in this area has been modest in the past because of the width and height of the natural shingle beach.
HR Wallingford has helped to form a conceptual model of coastal geomorphological processes to guide the future management of the beaches and the flood embankments around the harbour. Just as this study started, the spit to the west of the harbour had rapidly extended across its entrance, deflecting the low water channel out of its mouth. This had disrupted the eastward longshore drift and caused beach erosion at Pagham Beach Estate.
The main objectives of our involvement in this study were to:
To achieve these aims we undertook data analysis and numerical modelling of the changes in the plan-shape and the profile of the beach east of the harbour entrance. The plan-shape modelling was carried to reflect the uncertainties regarding future wave conditions and how much sediment might be transported across a future harbour entrance. The modelling of the changes in the profile of the shingle barrier beach took into account the prescribed allowances for the effects of climate change, for example an increase in mean sea level, to ensure that the probability of flooding of the houses behind the beach would be appropriately low.
Main image courtesy Simon Carey.