Despite adequate rainfall throughout the year, runoff is strongly seasonal in the
catchments draining into Slapton Ley . This is, in part, caused by high evaporation losses in the summer months but also because the deep permeable soils function like a shallow aquifer. Streamflow falls to a low level in the summer months ; high flows resume in the winter once the large soil moisture deficit has been recharged.
Despite the dominance of subsurface flow, there has been a significant increase in the incidence of surface runoff in recent years. The implications of this mixture of
hydrological pathways for the quality of water draining into the Ley are briefly discussed. Slapton Ley, itself is a shallow lake basin with a very low retention time in the winter. Outflow from the lake takes place mainly through the Torcross culvert but, in summer, when the water level is low, seepage through the shingle ridge is the only significant loss. Deposition of sediment during storm events is probably important at all times of the year and especially in the Higher Ley. In terms of eutrophication, the nutrient load of summer baseflow may be most important.