The Solent is a major estuarine system on the south coast of England with examples of four coastal plain estuaries (Yar, Medina, King’s Quay Shore and Hamble) and four bar-built estuaries (Newtown Harbour, Beaulieu, Langstone Harbour, Chichester Harbour). It has the largest number of small estuaries in the tightest cluster anywhere in Great Britain and is located in one of only a few major sheltered channels in Europe, lying between a substantial island (the Isle of Wight) and the mainland. The Solent and its inlets are unique in Britain and Europe for their complex tidal regime, with long periods of tidal stand at high and low tide, and for the complexity and particularly dynamic nature of the marine and estuarine habitats present within the area. There is a wide variety of marine sediment habitats influenced by a range of salinities, wave shelter and intensity of tidal streams, resulting in a uniquely complex site.
Most of the shoreline is exposed to a substantially less energetic wave climate and therefore less severe wave attack and shoreline erosion, than most of the English south coast. Erosional cliffed coasts can be found facing open water on the Isle of Wight and the Solent approaches. These prevailing conditions have allowed a wide range of coastal geomorphological features to evolve, such as barrier beaches and spits, dunes and soft cliffs, estuaries and rivers, harbours and lagoons. Much of the Solent shoreline receives natural coast and flood protection from severe wave attack, by the presence of the saltmarshes and extensive inter-tidal mudflats.
The offshore areas also show complex morphology with offshore banks and deeply-incised channels. The Solent generally has modest water depths which rarely exceed 20 metres, with localised deeps at Spithead and Hurst Narrows.
Large sections of the coastline have experienced extensive industrial and residential development, including land reclamation, and the seabed has been subject to dredging for navigational purposes and for offshore sand and gravel extraction.