Piping and pipeflow in a deep peat catchment

Abstract

Natural pipes are common in many upland blanket peats, yet little is known about pipe network morphology or pipeflow processes. Most information on soil piping comes from the shallow peaty podzols of the Welsh uplands, where monitoring suggests that pipes may be important contributors to streamflow. This paper presents information on piping and pipeflow from a deep upland blanket peat catchment in the Pennine Hills of Northern England. Pipe outlets are found throughout the soil profile ranging from the underlying substrate at ∼3-m depth to pipes which are within a few centimetres of the surface. Mean pipe diameters range from 3 to 70 cm; some pipes are over 150 m long. Slopes in the catchment are less steep than those usually associated with soil piping. Continuous flow records were obtained from 15 gauging sites on 8 separate pipes. The pipeflow response from deep blanket peat was found to be different to that reported in the shallow peaty podzols of the Welsh uplands; the distinction between ‘ephemeral’ and ‘perennial’ pipe types does not appear to be useful within the deep Pennine blanket peat. Response times from all of the pipes are short, even from pipes deep within the peat. At the same time pipes have a prolonged recession limb such that they maintain low flow for longer periods than most other runoff production processes within the catchment. Pipeflow contributes around 10% of the streamflow volume, but can at times contribute up to 30%. Soil pipes may, therefore, be far more important in some upland peat catchments than previous work has hitherto suggested.