Coastal erosion in the eastern half of Christchurch Bay

Abstract Christchurch Bay has a long history of shoreline recession and this has given rise to some major coastal engineering problems. An area of particular concern is Hurst Beach at its eastern end, where the maximum rate of recession has increased from 1.5 m a-1 (1867 to 1968) to 3.5 m a-1 (1968 to 1982). Hurst Castle itself is now subject to wave attack on part of its frontage. The littoral sediment movement was assumed to be essentially continuous around Christchurch Bay, but, in fact, a littoral drift sub-cell boundary (i.e. a partial barrier to littoral drift) is present in the vicinity of Hordle Cliff. Therefore, the increased recession of Hurst Beach is a local problem. Milford-on-Sea is situated on a thick sequence of Pleistocene Gravels, whose erosion contributed substantially to the maintenance of Hurst Castle Spit as a major physiographic feature. However, a series of coast protection works were constructed to protect Milford-on-Sea between 1936 and 1968, removing this important source of sediment. In the long term, without any further human interference, recession rates of up to 6 m a-1 will probably occur along Hurst Beach. A breach of Hurst Beach is a major concern, as it would create an island at Hurst Castle and expose the vulnerable, low-lying, northern coast of the West Solent, including the village of Keyhaven, to increased wave attack and tidal scour. Ecologically important saltmarshes would also be destroyed. Shingle renourishment is the only environmentally acceptable engineering solution. Limited renourishment has already commenced. Any cost benefit decisions must consider the wider implications of a breach in Hurst Beach, including environmental and ecological considerations. This case study demonstrates the importance of a detailed understanding of both the littoral and offshore sediment movement for the planning of coast protection.