Dye tracing in the Beacon Hill Pericline, East Mendips (UBSS Proceedings v.19(1))

Abstract: Repeat tracer tests using fluorescent dyes were made on four swallets in the Carboniferous Limestone Seven Springs cathment, East Mendip. Downhead Swallet feeds a predominantly vadose conduit, with a major distributary which underflows the Seven Springs but does not feed Holwell Spring. Dairyhouse Slocker is tributary to the conduit below this distributary, but the Bottlehead conduit is independent and feeds only the Main Spring. Dewatering at Torr Quarry has caused a change in the function of the phreatic conduit from Heale Swallet, which previously was tributary to the main Downhead conduit. The conduit has not been directly intersected by quarrying but diffuse leakage induced by the steepened hydraulic gradient towards the quarry captures all the flow. The Bottlehead Slocker conduit is similarly affected, with leakage being large at low flow, but insignificant at high flow. The Downhead Swallet conduit is affected least by quarry dewatering, because of its vadose nature and greater distance from the quarry. Nevertheless movement of water from the conduit into the diffuse flow zone does occur, particularly during periods of active swallet recharge.