The Eden valley or Vale of Eden is a fault-bounded basin, lying between the uplands of the North Pennines to the east, and the Lake District to the west (Figure G1). The main aquifer formations are the St Bees and Penrith Permo-Triassic sandstones, which are moderately permeable. The Carboniferous geology, which conprises layered limestones, sandstones, mudstones and coals also acts as a complex minor aquifer. Around 75% of the bedrock is covered by superficial deposits of variable lithology (clay-gravel size) and thickness (up to 30 m). Quaternary superficial deposits are important, consisting mainly of glacial till but also including alluvial soils, peat and river terrace/outwash gravels (see Allen et al. 2010).
Figure G1. Perspective view from the north east showing the Eden catchment bedrock geology. The black outlines indicate the three DTC subcatchments.
There is substantial abstraction of groundwater from the sandstone aquifers under the valley floor, supporting public water supply, industry and farm use. The minor aquifer can also support lesser abstractions and may discharge to overlying sandstone units or to surface waters. United Utilities extract 420 million litres of water from the Eden catchment annually, to supply Eden residents but also the Greater Manchester connurbation. The river Eden gains over most of its 145 km length, due to recharge from underlying aquifers. The groundwater resource and baseflows in the river Eden are at risk from increasing nitrate concentrations in response to agricultural intensification (see Butcher et al. 2003 & 2008).
The conceptual model hypothesises that the Quaternary superficial deposits are likely to control the hydrogeology of the DTC subcatchments. Investigation of these indicates complex lithostratigraphy. Interdigitations of sand, gravel, silt and clay may result in perched water tables, which may link to and interact with the stream network at catchment scale. These shallow groundwater sources may have short residence times compared to groundwater transfers through the main aquifers. The volume and residence time of the shallow groundwater is expected to influence the stream response to agricultural management practices.
Flow – quantity, timescale
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