Horsea Island

Horsea Island was an island located at the northern end of Portsmouth Harbour; gradually subsumed by land reclamation it is now connected to the mainland. Horsea falls within the city of Portsmouth and is wholly owned by the Ministry of Defence as part of the HMS "Excellent" shore establishment, which maintains its headquarters on Whale Island.


Horsea was originally two islands, Great and Little Horsea, the former large enough to support a dairy farm. The islands were joined to form a torpedo testing lake in 1889, using chalk excavated from Portsdown Hill, 1 km to the north, by convict labour. aircrew often sustained serious compression injuries to the spine after ejecting from submerged aircraft.

After closure of the telegraphy station in the 1960s, the northern part of the island became home to HMS "Phoenix", the naval school of firefighting and damage control. The school comprised a number of steel structures (:'trainers'), simulating three decks within a warship. Fires were set in the trainers for the purposes of instruction in various types of firefighting."The Portsmouth Papers", No. 36: Horsea Island and The Royal Navy. Portsmouth Museums, Portsmouth. ] . The kerosene and water mix burned in the trainers, known as "sullage" caused significant water and air pollution and created a health hazard for the staff exposed to the fumes for protracted periods. In 1994 the school removed to a modern gas-fired trainer on Whale Island as part of a consolidation and cost effectiveness initiative. The new facility is known as the Phoenix school of Nuclear, Biological and Chemical Defence, damage control and fire fighting.

Responsibility for training and site management was contracted out to Flagship Training UK, which was taken over by Vosper Thorneycroft in September 2008.

Current use

The original island site continues to be used by the MoD, with a number of facilities on the site predominantly focussing on diving and underwater engineering. Infrastructure includes training facilities as well as workshops, decompression chambers and equipment testing capabilities. Organisations on the site include:
*The Superintendent of Diving, a Commander, Royal Navy, who is responsible for safety and standards of diving in the Royal Navy and Royal Engineers.
*Maritime Warfare School delivers the Defence Diving School, providing new entry diving training for RN and RE divers as well as promotion courses as divers progress in their careers.
*Headquarters of the Fleet Diving Squadron, which delivers diving, underwater engineering and bomb disposal capabilities in the UK and overseas using the Northern and Southern Diving Groups, and the Fleet Diving Group.
*Southern Diving Group (East)
*Fleet Diving Group
*The Sea Survival section of Phoenix.The lake is also used by civilian diving schools and clubs and is open to recreational divers on a regular basis.


In the early 1970s, the tidal mudflats between the island and mainland at Paulsgrove to the north were reclaimed, much of the area destined to become a landfill site, the remainder to form the Port Solent leisure complex. The landfill site closed in 2006, and waste is now incinerated at a plant in east Portsmouth. The northern part of the reclamation has been developed as 'Port Solent', a complex comprising a marina, multiplex cinema, housing, retail outlets, and some business units known collectively as the 'North Harbour Business Park'. The rest of the landfill site is being developed as a recreational park featuring woodlands and meadows.


The solid geology of the site is Upper Chalk, covered by post-glacial drift deposits comprising mostly brickearth, a loess from the west of England eroded and deposited downstream by the river system which once occupied the area now known as the Solent and its margins before inundation by the sea. Much of these deposits were covered by the chalk fill imported from Ports Down to create the torpedo lake. Where still exposed, beyond the lake at the eastern end of the site, the brickearth comprises fairly equal proportions of sand, silt, and clay, with occasional flints. Owing to the high clay content, the rock is of low permeability, occasioning flooding after prolonged rainfall during winter. In the extreme south east corner of the site, brick and concrete rubble has been used to construct the bunding to enhance protection from the rising sea.

Horsea Lake

The lake, which contains a wealth of marine life, has a number of items placed for diver training including a helicopter, vehicles and a 200 year-old ship wreck, placed in the central section. The level of the lake is maintained naturally by two submerged freshwater springs.


All of the undeveloped area to the south of the lake, with the exception of the helipad, forms one of the few terrestrial parts of the Portsmouth Harbour Site of Special Scientific Interest (SSSI) on account of the rare flora and fauna Hooper, S., Smith, D. & Tomlinson, N. (1991). "The COPSE* Report" (*City Of Portsmouth Survey of the Environment). Portsmouth Urban Wildlife Group, Portsmouth. (Private publication)] which have flourished on the imported chalk, notably the Small Heath butterfly "Coenonympha pamphilus" (a UK BAP High Priority species now extinct on Ports Down); Horsea is also the only known habitat of the micromoth "Eulamprotes immaculatella" in Hampshire. The SSSI area is in poor condition however, owing to overgrazing by rabbits, and the withdrawal of Highland cattle introduced to control the scrub.

The eastern extremity of the former island, beyond the SSSI, has been used as an elm trials site for the evaluation of new disease-resistant cultivars since 2001, and currently accommodates 30 trees comprising 14 cultivars and exotic species. The site's English Elms "Ulmus procera", were home to a colony of rare White-letter Hairstreak "Satyrium w-album" butterflies until 2000, when a resurgence of Dutch elm disease killed the remaining semi-mature trees.

Portsmouth Football Club

In October 2007, Portsmouth F.C. announced plans to build a 36,000 seat football stadium on the south-east corner of Horsea Island, near to the M275 motorway. The proposed new stadium at Horsea Island is planned for completion in 2011 [cite news |title=Pompey switch site of new stadium|url= |publisher=BBC Sport |date=2007-10-26 |accessdate=2007-10-27] [cite news |title=Portsmouth outline stadium plan|url=|publisher=BBC News|date=2008-06-19|accessdate=2008-06-25] . Serious logistical problems, notably the paucity of access by road and rail (the nearest railway station, Cosham, is 6 km away), need to be addressed by plans yet to be made public, but indications are that two new junctions are to be constructed off the M275 as access to the new stadium which will also facilitate development of the nearby Stamshaw area. A railway station at Wymering has also been proposed, but this would still be 3 km away from the proposed stadium. There are question marks over the proposed housing development essential to help fund the stadium. The original schematic plan published in The News when the stadium proposal was revealed clearly showed housing south of the lake impinging on the western end of the SSSI, which if correct would be a serious obstacle to planning permission.

However, the most fundamental problem is the site's vulnerability to flooding. Less than 1 m above sea level, part of the site is already regularly inundated by sea water on spring tides. Moreover, in a study led by the US National Center for Atmospheric Research, sea levels are predicted to rise six metres by 2100 which, if correct, would see Horsea, like the Maldive Islands, submerged before 2040 Overpeck, J. T., Otto-Bliesner, B. L.,Miller, G. H., Muhs, D. R., Alley, R. B. & Kiehl, J. T. (2006). Paleoclimatic Evidence for Future Ice-Sheet Instability and Rapid Sea-Level Rise. "Science", 24 March 2006, Vol 311, no. 5768, pp 1744-1750 ] [] . A formal planning application has yet (July, 2008) to be submitted.


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