Problems of Protection Against Piping and Surface Erosion in Central Tunisia

Abstract

The formation of quasi-tubular voids in the subsoil, known as ‘piping’, is an important form of subsoil erosion that arises when substantial volumes of subsurface lateral throughflow pass through dispersible subsoils. Amongst the environmental factors that favour the development of piping are high contents of expansible clay minerals, a severe dry season, and convexities in the slope profile. The first two of these are characteristic of considerable areas in Central Tunisia. In addition to natural slope-convexities, further topographic loci for pipe initiation and development are provided by the artificial convexities introduced into the slope profile by the construction of conservation banks. The earthworks are designed as protection against surface erosion processes, which prevail for most of the year in this part of Tunisia. However, it appears that the banking is particularly vulnerable to piping, which is causing considerable disruption. Australian experience indicates that banking should be used very sparingly on soils which are at all prone to piping, and that care is needed in both the alignment and construction of such banks as are deemed unavoidable.