Recent coastal protection and associated temporary exposures to the Middle Eocene coastal sections at Lee-on-the-Solent, Gosport, Hampshire
by D.J.Kemp MPhil, Keeper of Geology
Hampshire County Council Museums Service, October 1999Recent coastal protection work at Lee-on-the-Solent, Gosport, Hampshire has had a substantial effect on the foreshore. This paper examines the impact on this nationally important Middle Eocene, (Barton and Bracklesham Group), geological Site of Special Scientific Interest (SSSI).
The changes to this site before, during and after contract completion and the long-term effects are examined. The engineering impact is discussed, additional geological and palaeontological data is recorded and two comprehensive faunal lists are given.
On-going groyne damage, associated beach loss and subcrop erosion, followed by a recent sea wall failure at Lee-on-the-Solent, Hampshire, have all individually contributed to the need for this major coastal protection initiative. This scheme and the increased erosion have provided numerous opportunities to collect from and record new exposures in the Barton Clay and Selsey Formations, Barton and Bracklesham Groups, Middle Eocene. The coastal protection work is now completed and has resulted in the almost total covering of the lower foreshore by imported sand, gravel and rock. Future developments here will therefore require close monitoring.
History of coast protection and erosion
The succession and stratigraphy of the Barton Clay & Selsey Formations at Lee-on-the-Solent was first described by Fisher (1862) and more recently by Kemp, King, King and Quayle (1979) and Kemp (1985). Since then, changes to the Middle Eocene stratigraphic nomenclature include relegation of the Elmore Formation to Member status and the adoption of the Selsey Formation by Todd (1990). The cliff in central area [SU 5616 0051] formerly the site of Lee pier and the near-by railway terminus was protected by a sea wall in the latter part of the 1880s (see Edelman 1993 and Burton & Peacey for details).
The remaining wave washed cliff at Lee-on-the-Solent and Elmore was protected by a sea wall and wooden groynes in the early 1960s. Clearly coastal erosion and longshore drift is controlled by the tides and weather, particularly gale force winds, the most devastating of which are well documented by the meteorological office, these include the "Great Storm" of 15th-16th October 1987, followed by the January storms of 1990. During the 1990 storm the local coastguards recorded south-westerly winds with gusts exceeding 100mph over the Solent.
The original gravel capped cliff and shingle beach at Lee-on-the-Solent, looking north-west towards Monks Hill, Hill Head, on the lower foreshore weed covered nodules of bed L7, can clearly be seen extending out into the sea from the beach toe c1920.
The already greatly reduced beach slope aggregates at Lee-on-the-Solent, between [SU 5630 0030 & 5602 0070] were further reduced by these storms, also some localised wooden groyne failure was noted. In addition, substantial undercutting of several crucial wooden groynes occurred; this clearly accelerated the erosion of underlying clay.
Beach slope and toe erosion showing narrow exposure of the Selsey Formation and undercutting of wooden groynes (arrowed), looking south-east towards groyne 6, Lee-on-the-Solent, March 1997
Following this, one area of Lee-on-the-Solent beach centred around [SU 5614 0050] never properly recovered with new, previously unseen clay exposures sporadically appearing at the beach toe and in various positions on the beach slope. By the latter part of 1991, the reduced beach shingle levels and concentrated erosion necessitated remedial buttress work along the base of the higher, central section of the sea defences. Also, nearby at [SU 5629 0014], there was complete failure of one short section of sea wall , originally built by the Lee-on-the-Solent Railway Company in 1894 Mitchell & Smith (1986). The resulting exposure and other associated exposures are included in the following text.
Sea defence failure looking north-west towards central part of Lee-on-the-Solent, 18 January 1992
More recently a coastal survey of Lee-on-the-Solent was commissioned by the Gosport Borough Council, who were reviewing the on-going maintenance problems of the ageing concrete sea defences and wooden groynes.This survey recommended the construction of rock groynes and advancing the shore line by reclaiming with new shingle Cooper & Harlow (1998), rather than encouraging the least disruptive option of holding the line by beach recharging between the fully restored, existing wooden groynes Brampton (1998).
In September 1996 the appointed contractor Dean & Dyball commenced work on the 11 rock groynes under the supervision of Sir William Halcrow & Partners, consulting engineers to the client. Groyne construction was completed by late March 1997 and the beach regeneration using aggregates dredged from Southampton Water was completed by July 1997.The adopted proposal appears not to have fully recognised the significance of this internationally important, geological SSSI and that the Lee-on-the-Solent section is one of only three known coastal localities of this age in Europe (see site notification, English Nature 1992, and Hooke 1998 for details).
Beach regeneration between groynes 6 and 7, Lee-on-the-Solent 1997.
In addition, the comprehensive faunal list recorded here since 1960 includes evidence of rare, previously unrecorded invertebrate & vertebrate fauna and more importantly thirteen unique scientific species (see Collins & Quayle 1981, Crane & Quayle 1986, Harrison & Walker 1979, Quayle 1987, Ward 1977 and Ward 1978 for details
The author wishes to express his sincere thanks to the project manager/contract engineer, Dr Roger Maddrell (Sir William Halcrow and Partners, Consulting Engineers), for making site plans available and for giving permission to use them in the printed version of this paper.
Ms Rachel Fowler, resident engineer, gave permission to visit the site. Mr Steve Kenny and his colleagues from Dean and Dyball are particularly acknowledged for on site co-operation and friendly manner in otherwise frequently difficult working conditions.
Mr. Ian Edelman and Mr Stephen Locke critically read the manuscript, also Dr Chris King gave valued comments on the main elements of the text and kindly helped with the speciation of the mollusca collected from the Barton Clay Formation.
Mr Alan Kemp, Mrs Elizabeth Kemp and Mr Brian Forhead are each thanked for their active assistance on site, Mr Brian Forhead, also helped afterwards preparing and sorting samples in the museum laboratory. Mr Mike Jurd provided additional vertebrate records from the groyne 2 excavations and Mr Steve Tracey is thanked for his help with speciating the mollusca collected from the Selsey Formation.