What is the Solent?

Strictly speaking the Solent is the area of water bounded in the west by Hurst Narrows and in the East by the Palmerston forts. However SPS interests extend to the view from the water and the immediate shoreside facilities. The shaded area on the map gives an approximate; idea of our interests. See also “About the Solent”

Solent Map

The Solent Forum have assembled many facts about the Solent in their Solentpedia website

 Geological History – Summary

[Source: Solent Estuaries – Introduction: Geology of the Wessex Coast of Southern England by Ian West]

The Solent Estuarine System consists of Southampton Water, the West Solent, the East Solent and Spithead, Portsmouth, Langstone and Chichester Harbour. These are all drowned Pleistocene river systems above Tertiary (mostly Eocene) clays and sands with minor limestones. The Solent River extended from west to east and swung round the eastern end of the Isle of Wight at a time when sea-level was low and the English Channel was dry.  This river channel has a series of terraces which descend to about 40 metres below sea level at the east of the Isle of Wight. The old valley is now flooded and is quite wide and relatively straight with coastal erosion at the margins.

Southampton Water is above the Pleistocene valley of the combined Test and Itchen and resembles in Solent in general geomorphology, except that the upper parts are not subject to significant coast erosion. However, from the Hamble Estuary southward coast erosion is now increasing. The Beaulieu River Estuary, the Hamble Estuary and the Itchen Estuary have incised meanders. The meanders may have developed on a Hoxnian marine surface, the Slindon Boxgrove Raised Beach (at about 30m). As sea-level fell during the Devensian, they were incised, even though the subsequent glacial phase rivers were probably of braided rather than meandering type. Meanders are only visible on a map where only the lowest gravels are flooded and the higher, wider terraces are not under water. There is also a well-developed incised meander in the former Test Valley under the West Quay Shopping Centre, Southampton (reclaimed land).

The eastern estuaries, Portsmouth Harbour, Langstone Harbour and Chichester Harbour are quite different. They represent short dendritic river systems, that are approximately limited to the north by the former cliff line of the Ipswichian Raised Beach (of the Selsey – Portsmouth area). The river system has originated in Devensian times on this beach and low level terrace. It has fairly steep slope to the outflows at the narrow harbour entrances (further narrowed by spit developments). The buried channels at these harbour entrances are at about 20m below sea-level (and may be slightly more).

The underlying geology is well-known from numerous shallow engineering boreholes (many thousands), and a few deep boreholes (e.g. Southampton No.1 and Marchwood No.1). There have been studies of sections in the Fawley Transmission Tunnel (under Southampton Water), the Fawley Outfall Tunnel (into the West Solent), the Sewage Outfall Tunnel from the Gosport area, the water pipeline excavations from Lepe southward, the study for the proposed railway tunnel from Lymington, etc. In addition there are coastal exposures in the Solent and there have also been geophysical studies. There are British Geological Survey memoirs and geological maps of the area, numerous papers and other publications. The geology is fairly simple. It is an easy area to study, assuming you have a basic knowledge of the local   Eocene.