Runoff generation and water table fluctuations in blanket peat: Evidence from UK data spanning the dry summer of 1995

Understanding of the hydrology of upland blanket peatlands has been limited both by the logistical difficulties of obtaining data from such environments and by technical difficulties with plot scale investigations of peat hydrology. The relative importance of infiltration-excess and percolation-excess as runoff generating mechanisms as opposed to the saturation-excess mechanism remains unclear. This study uses catchment-scale runoff data, in combination with monitoring of water table levels, to identify the relative importance of these mechanisms for an upland peat catchment within the Moor House National Nature Reserve in the UK. Mean runoff coefficients for the catchment are 0.4 and the flood hydrographs are flashy. Monitored water table in the catchment is within 5 cm of the surface (i.e. within the acrotelm) 93% of the time. High stream flows always occur at times of high water table suggesting that overland and near surface runoff is controlled by saturation of the catotelm rather than by infiltration capacity. Depressed rates of water table recovery at the end of a prolonged period of low water table in 1995 suggest possible physical changes once the peat has dried out. The likelihood that such periods of low water table will become more common under global warming scenarios raises concern over the impact of such changes: increased erosion, water discoloration, and increased CO₂ flux may result.