Título:
Mechanisms of flooding in the Mawddach catchment
Resumo:
A research project is in progress to model flooding in the Mawddach catchment, North Wales. A range of field investigations has been carried out to help in the selection of appropriate computer models. Rainfall distribution recorded at 22 raingauges does not correlate well with ground elevation, suggesting instead that maximum precipitation is generated at valley heads where maximum uplift of air masses occurs. Streams within the Mawddach catchment have their sources in upland blanket bogs; water table monitoring shows the water storage capacity of older humified peat to be very limited, with saturation possible during a single storm event. Large thicknesses of glacial and periglacial deposits infill river gorges in the catchment; saturation of these deposits can create conditions for rapid runoff and flooding downstream. Temperature monitoring of river bed sediments has identified resurgence of groundwater after prolonged rainfall. It is concluded that surface water and groundwater interactions are essential for the modelling of antecedent effects on storm runoff. Surface water models predict that floodplain forestry within the catchment can provide significant temporary storage for peak discharge, reducing flood levels downstream.
Autores:
Graham Hall, Roger Cratchley