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| Breckland |
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| Habitat: Rivers and streams (of local significance) |
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Rivers and streams from bank top to bank top, including the open water area, fringing vegetation and exposed sediments.
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Three westward-flowing rivers and their tributaries incise the low plateau of Breckland. TheLittle Ouse, Lark and Wissey with their tributaries comprise some 240 kilometres of riverwithin the Natural Area. All are chalk rivers fed by groundwater, which can contribute up to70% of total annual river flow. They drain an extensively arable upland catchment. Therivers and their major tributaries, the Thet, Sapiston/Black Bourne and Watton Brook, rise tothe east in the East Anglian Plains Natural Area. The three flow to the Ely-Ouse or, in timesof flood, are diverted into the Cut Off Channel and then to the Tidal River via the ReliefChannel, downstream of Denver. On average they contribute to the flow of the Ely-Ouse asfollows; River Wissey 17%, River Little Ouse 36% and River Lark 12%.
A remarkable feature of the Norfolk rivers is their use to transfer groundwater, which can bepumped from a selection of river support boreholes in the Thet and Little Ouse sub-catchments, to meet public water demands in Essex. In especially dry years this watersupplements that which is diverted at Denver from the Ely/Ouse river into the Cut OffChannel to be subsequently pumped from the Cut Off Channel at Blackdyke through tunnels,pipelines and Essex watercourses to major reservoirs in south east Essex.
Water quality in these chalk rivers is typically good with beds of aquatic and emergent plantssuch as water-crowfoots, pondweeds and reed and branched bur-reed abundant on gravellysubstrates. Riffle-pool systems exist on most upstream sections, with the river Wissey beingthe finest example. Brown trout breeds on the Lark, Wissey, Thet and parts of the Sapiston. Angling for this species is a widespread activity on the Lark and Wissey supported bystocking and natural populations. Trout are absent from the Little Ouse which supportsroach, dace, chubb and pike. The native white clawed crayfish has been recorded inBreckland rivers.
Otters are an important species on Breckland rivers, their natural populations having beensupported by careful introduction programmes in recent years. Breeding is confirmed andthis elusive animal makes good use of the carr woodlands for shelter. Water vole is anotherimportant species but there is little knowledge of its Breckland population trends which maymirror a national decline. Other typical species of rivers include dragonflies and damselfliessuch as the beautiful banded demoiselle. Breeding waterfowl include mallard, tufted duckand gadwall.
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