The Cadland to Calshot Coastline

In response to many requests from GCSE and 'A' level geography students, this page has been designed to give information about the Cadland to Calshot coastline which, it is hoped, will help with project work being undertaken. The Field Studies Department at Calshot does not engage in primary research work, but we do collect information gathered by students on field courses at the Centre. Some of this is presented here. See Data (182Kb). If there are gaps, or you have suggestions for other topics that we might add to these pages, please e-mail the Field Studies Department

GEOLOGY

This section of the Hampshire coast forms an area approximately one kilometre in length, from Stonepoint in the west to Calshot in the East, and is primarily post glacial in origin. The Cadland cliffline in Stanswood Bay comprises of an eight hundred metre section situated about 600 metres to the west of Calshot. See Maps A (118Kb)and B. (137Kb) The cliff line is composed of fluvial gravels and sands which are superbly exposed. The cliffs expose terrace gravels of the Solent River system. Although the Solent River no longer exists, since most of its course has been drowned by eustatic sea level rise during the Flandrian, it previously flowed in an easterly direction across south-east Dorset and south Hampshire as an extension of the River Frome. At the end of the last ice age, sea level rises drowned this system, and marine erosion began to mould the Hampshire/Dorset coast.

GEOMORPHOLOGY

Because of their friable nature, the cliffs at Cadland have been rapidly eroded backwards. The process has largely been one of 'cliff retreat' as the sea has 'undercut' the sand/gravel layers. Evidence for this rapid erosion is plentiful and easily seen on the cliff and beach. See Cliff Photos (185Kb). As such the cliffs may be seen as being particularly 'active' geomorphologically.

Longshore drift on this coast is primaily SW to NE, and the gravels released from the cliff form a large proportion of the beach sediment. Sediment is moved east, evidence being found in the the effects of 'attrition' upon pebble size. See Data (182Kb). As one moves west towards Calshot, it is possible to see the effects of LSD and deposition in the increased width of the beach. The effects of this process on the cliff line are also evident in the way that cliff erosion reduces to the point where the cliffs become extremely stable. Their angle reduces from the 70/80 degrees of the eroded cliff to 35/45 degrees below Calshot Village. The protective effects of the beach are therefore well seen, absorbing wave energy before the cliffs can be effected. The human response to this is to 'colonise' the upper shingle with a variety of small and large beach huts, some of which are akin to small bungalows. See Beach Photos (42Kb).

As one progresses further East, so the width, height and steepness of the deposited beach increases, and the height of the cliffs reduces until we reach the pre-glacial turn in the coast line just past Calshot Village. See Data (182Kb). At this point the coast turned sharply North, towards present day Southampton. At the end of the last ice age (+/- 10,000 years BP), gravel was reworked on the shore by rising sea levels to create Calshot Spit. LSD processes have subsequently moulded the spit into its current position. Wave energy falls markedly as one approaches Calshot Spit, and the deeper water that lies just offshore. Consequently, depositional processes dominate. The spit is some 600 metres long, with a substantial recurve created by the interaction of currents down Southampton Water with those of the east and west Solent. See Spit Photos (32Kb). The deposition is historically stable, and the first permanent human use took place in the form of the building of Calshot Castle by Henry VIII in 1539. See Castle Photos (32Kb).Later, in 1904, an airbase was established on the spit, which grew to become a large base during the first and second world wars. In 1963 Hampshire County Council took over the site to develop Calshot Activities Centre, the largest outdoor education centre in the country.

RECENT GEOGRAPHICAL CHANGES

After 10,000 years of relative stability, this coastline is beginning to show signs of accelerated change. Areas of formally stable cliffline to the west are revealing some signs of increased erosion/undercutting at high tide, and Calshot Spit has been inundated several times in the early 1990's. The cause of this is under debate, but may be related to the building of protective groynes below the western cliffs in the 1960's. These are largely degraded today, although some sections have been renewed. Additionally, it is likely that global sea level changes will have an impact upon the spit, which effectvely lies at sea level.

Action to offset major flooding was carried out in 1994/5 by New Forest District Council, who constructed a series of revetment and groyne defences along Calshot Spit. See Management Photos (57Kb). This has resulted in a slowing down of the erosion rate noted in the early 1990's, and a rapid increase in beach height on the south facing side of the spit. Unfortunately, these groynes were not built all the way along the spit, and the north eastern end has recently revealed some signs of stress from high tides.