Soil Piping and Stream Channel Initiation

Abstract

The hydrologic significance of soil piping has been generally ignored. Piping has been associated primarily with drylands, yet evidence of piping is available from a large range of climatic regions. In particular, soil piping is found to be widespread in the United Kingdom. Preferred locations for piping are either just above or within a horizon of low relative permeability and low aggregate stability. Chemical environment may range from acidic moorland soils to saline marshes. There are significant trends to lower aggregate stability and coarser grain size (particularly in the range above 250 μm) in the bed of a pipe than in the roof. Many pipes in the areas studied appear to be dormant or relatively inactive and may well be in approximate equilibrium with the soil pore and channel subsystems. However, when equilibrium is destroyed (e.g., by stream incision) pipes can form loci for channel extension. Studies of the spatial distribution of outlets show that to create normal channel networks, pipe clusters within the ensemble and, similarly, individual pipes within those clusters must be selected on an unequal basis. A low density random selection from pipes located on percolines would fulfill the requirements. The presence of piping may have a significant effect on the form of the hydrograph.