In the last 200 years, there has been significant erosion of the mudflats off the coast of western Hampshire, particularly in the area around Lymington. Today they are receding at the rate of four metres a year. This steady decline, which can be attributed to seas level change, threatens a nationally important nature reserve that is home to many rare wader birds.
However, the erosion has another, less obvious impact. As the mud recedes, a buried, prehistoric landscape is being exposed. Primarily this landscape consists of peat deposits, which can be compared to the upper peats of Bouldnor Cliff on the other side of the Solent. Initially, the main focus of investigations into this landscape was the area of mudflats between Hurst Castle to the west of Lymington, and Pitts Deep, halfway between Lymington and the mouth of the Beaulieu River.
Various methods were used to identify and record the peat beds; drift dives allowed divers to view and record changes in the seabed over large areas, whilst spot dives were carried out at specific locations where an underwater cliff had been identified. The peat deposits were sampled using an auger core. All of the information gathered in this way, started to build a better picture of the landscape that existed when the Solent was a river valley and area of habitation, before becoming the drowned valley which we see today.
In 2001, this project gained a massive boost when SEA Ltd (Submetrix) carried out a swath bathemetric survey of the north-west Solent coast, in the area of the mouth of the Lymington River. The high resolution data produced has provided detailed information on the submerged deposits, which has allowed us to plot the underwater cliff that marks the extent of the deposits. This enabled diving to target very specific areas of interest, including the cliff at the deposits’ edge and interesting channels which may be the remains of palaeochannels.
During 2001 and 2002 survey, monitoring and sampling were carried out at several sites. At Tanners Hard, east of Lymington, erosion was uncovering more peat and submerged land surfaces each year. Samples were taken from a section of underwater cliff, radio carbon dated and analysed. The results of this work revealed an interesting sequence of environmental changes connected to the formation of the Solent River and the severing of the Isle of Wight from the mainland. Monitoring pins are now in place at Tanners Hard to measure rates of erosion.
The area west of Hurst Spit was also subject to survey; initial drift dives identified further peat deposits. The seabed in this area is subjected to different tidal and biological regimes, which have resulted in the peat being heavily scoured and pitted.
In 2009 Hawker’s Lake at Keyhaven was surveyed. This site nestles in the shelter of Hurst Spit and contains the remains of a landscape drowned thousands of years ago. Visible on the seabed are trees and vegetation entwined within peat deposits. Until recently these deposits were entombed within marine clays which had protected them; only now are they being revealed by coastal erosion. Samples of the ancient forest were collected, which will tell us about the past environment when this part of the Solent was dry land.
More recently, a large abandoned anchor of unknown date was discovered embedded in the seafloor. This was recorded, but further study may reveal the origin of the anchor.