Abberton Reservoir

Edersee Dam on 17 May 1943

Abberton Reservoir was first filled just before the start of World War II in 1939, and the Ministry of Defence was concerned that it might be used by German seaplanes as part of a possible invasion. To prevent this, 312 naval mines, anchored by steel cables, were laid in a grid across the reservoir. Steel cables were stretched across the part of the reservoir nearest to the pumping station, since exploding mines might have damaged the building. Some were inadvertently detonated by ice, but most were exploded after the war by soldiers firing from the banks.[7]

A German Heinkel bomber returning from a raid on Hornchurch airfield was shot down over Abberton on 24 August 1940. One of its crew bailed out from the burning plane and was captured; another drowned.[7]

The reservoir was used by the RAF's No. 617 Squadron ("The Dam Busters") for practice runs for attacks against German dams in the Ruhr during World War II (Operation Chastise). The reservoir was intended to simulate the Edersee Dam in Germany.[8] Lancaster bombers fitted with special bouncing bombs designed by Barnes Wallis were used in these trials,[9] and military police closed the causeway whilst the practice runs took place.[10] The last practice flight to Abberton was a full dress rehearsal of the Ruhr attack, and took place on the night of 14 May 1943.[11] The actual attack on the dams in Germany took place two nights later on 16 May 1943.[12] The Edersee Dam was attacked and breached after the Möhne dam had been successfully destroyed.[13]

The reservoir's current owners, Essex and Suffolk Water, part of the Northumbrian Water Group, recognised by 2007 that its capacity was insufficient to meet growing local demand,[14] and initiated a £140 million project to increase the capacity to 41,000 megalitres (9.0×10⁹ imp gal) by raising its banks. The scheme was completed in 2013,[2][5] and included replacing the existing link from the Stour to Abberton with new, higher capacity, pipes following a different route and extracting water at Wormingford instead of Stratford St. Mary.[2][15]

The other major part of the project was to enable the transfer of water from the Ouse, 141 km (88 mi) distant in Norfolk,[6] to the reservoir via the Stour.[2] Existing pipelines and associated infrastructure such as pumping stations carried water from the Ouse at Denver to Kirtling Green. From there, a new 15.5-kilometre (9.6 mi) tunnel was constructed to Wixoe, where existing pipelines completed the transfer to the Stour.[14][16]

The reservoir has a current maximum area of 535 ha (1,320 acres), and has three sections separated by the Layer Breton and Layer de la Haye causeways. The easternmost large, deep Main section, originally 410 hectares (1,000 acres) was enlarged to its current 535 ha (1,320 acres) in 2013, the Central section covers 49 ha (120 acres), and the Western section is 16 ha (40 acres).[5] The current maximum water depth is about 17 m (56 ft), 3.2 m (10 ft) more than before the enlargement.[2]

In wet years, Abberton and the other major Essex reservoir at Hanningfield can meet the requirements of the 750,000 people they serve in Essex and north east London using only water from the Stour and other local sources, but in average years 7% of the inflow involves transfers from the Ouse, rising to 35% in times of drought.[17][14]

Abberton is internationally important for gadwalls (male shown)

Abberton had been a winter roosting site for cormorants from the 1950s, and became the first tree-nesting colony in England when eight pairs bred there in 1981. There were 584 pairs by 1993, although numbers have since declined to around 180 pairs. Little egrets first nested in 2014, numbering 31 pairs by 2019, and a pair of cattle egrets bred in 2020. The area holds around 20 pairs each of Cetti's warblers and nightingales. Typical farmland species such as the corn bunting, yellowhammer and barn owl also breed in the protected areas. Up to eight pairs of little ringed plovers breed on the re-profiled margins of the reservoir.[5]

Abberton is a major site for wintering wildfowl, and has the largest numbers of any UK inland water body, typically holding around 35,000 individual birds, but rising to well over 40,000 in hard winters. It is of international importance for wintering gadwalls, shovelers and wigeons, and of national importance for mute swans, teal, pochards, tufted ducks, goldeneyes, coots and great crested grebes. Many ducks also moult during their stay at the reservoir. There are significant numbers of waders in winter, including black-tailed godwits, ruffs, lapwings and golden plovers.[5] In winter, bitterns occur regularly at the western end of the reservoir, and hen harriers, merlins, peregrine falcons and marsh harriers hunt over the bordering grassland; the last species has sometimes summered.[5]

Its proximity to the coast means that Abberton may hold scarcer species like smews and long-tailed ducks, and rarities including a blue-winged teal (1996), Britain's first canvasback (1997–2001) and a lesser scaup (2004–2005).[5] Rare terns include gull-billed, which bred in 1949 and 1950, Caspian, whiskered and white-winged black, five of the last species being present together in May 2019. Other recent rarities include ortolan bunting (2019), Bonaparte's gull (2017, 2019) Franklin's gull (2016) and desert wheatear (2012). There have been multiple records of red-footed falcons and red-rumped swallows over the years.[5]

A bird ringing scheme has operated at Abberton for more than 70 years, 90,000 ducks having been ringed in that period, including 40,000 teal. Recoveries of ringed birds have established national longevity records for 10 species, including wigeon (34 years), pochard (22 years) and gadwall (21 years).[5]

Anthribus fasciatus

Abberton has otters, water voles and brown hares, and eight species of bats, and other vertebrates include the common lizard, grass snake and great crested newt. Insects present include two rare weevils, Rhynchites auratus, which feeds on blackthorn, and a fungus specialist, Anthribus fasciatus.[5]

Introduced American signal crayfish are a problem in that they are larger and more prolific breeders than the native white-clawed crayfish, and eventually displace the latter species. They also burrow into river banks, which at Abberton may reduce the area available for aquatic vegetation and increase the amount of sediment entering the reservoir from the Layer Brook.[18]

Abberton was designated a Special Protection Area on 5 December 1991 as a result of its over-wintering populations of golden plovers, gadwalls, shovelers and teals, and for its breeding population of cormorants. There are also significant numbers of black-tailed godwits, lapwings, coots, goldeneyes,[19] tufted ducks, pochards, pintails, wigeons and great crested grebes.[19]

It is an internationally important wetland that was designated as a Ramsar site in 1981,[1][20] and became a Site of Special Scientific Interest in 1988,[21][22] three years after Hanningfield Reservoir received the same status.[23]

A small part of the site is managed as a nature reserve by the Essex Wildlife Trust.[24]