Hydrological Summary for the UK: June 2007

[摘要] Over the next few years decommissioning work at the UKAEA Winfrith site will require the water table around relevant work areas to be lowered by pumping groundwater from the underlying aquifer. The anticipated discharge for these works is 15 l/s, although occasionally flows may reach 30 l/s, and will discharge into a ditch at the north of the site, which discharges into a sub-channel of the River Frome. Since the River Frome is an SSSI over much of its lower reaches, a preliminary assessment of the likely impacts of this discharge on vulnerable species was made and a list of subsequent work was proposed. The River Frome between Dorchester and Wareham is a Site of Special Scientific Interest (SSSI) and a candidate Special Area of Conservation (cSAC). Maps of the extent of the SSSI are given along with the reasons for its designation as a SSSI. The discharge has potential to disrupt the typical water crowfoot habitat in the river and may affect several vulnerable species, including: Otter (Lutra lutra), Water Vole (Arvicola terrestris), White-Clawed Native Crayfish (Austropotamobius pallipes) [now thought to be extinct in the R. Frome], Southern Damselfly (Coenagrion mercuriale), Desmoulin��s Whorl Snail (Vertigo moulinsiana), Fine-lined Pea Mussel (Pisidium tenuilineatum), Medicinal Leech (Hirudo medicinalis) native Brown Trout (Salmo trutta), Brook Lamprey (Lampetra planeri) and Salmon (Salmo salar). Exploratory investigations suggest that the volumetric flow in the river is two orders of magnitude greater than the flow in the ditch itself. As a result, the volume of the discharge is not likely to affect the main river, although any vulnerable species present could be affected, particularly during natural low flow periods during the summer. In contrast, the quality of the water, particularly pH, alkalinity and some heavy metals, discharged to the ditch from pumping could potentially impact the river. Water Quality will vary widely, depending on the location of the pumped source within the Winfrith site and so the effect of each location will need to be considered individually. Visual observation of the ditch shows clear evidence of a significant movement of particulate material, which could impact on the river if flows are maintained at higher than normal levels during pumping. Nearby are potentially confounding influences from the Wool sewage works discharging 200m upstream of the ditch and two small rivers, the Win and the Bovington stream, which have a similar sized discharge to the ditch and discharge into the R. Frome approximately 1km downstream of the ditch.

[发布日期] 2007-07-13 [发布机构] NERC/Centre for Ecology & Hydrology

[效力级别] Hydrology