Erosion Intensity in a Mountain Watershed in the Himalayan Region

A simple method for mapping of erosion intensity in a mountain watershed based on assignment of qualitative indices to various categories of geomorphic features, mean ground slopes and lithological cum structural state of the bedrock is proposed.

A preliminary case study has been conducted in a part of the Ravi drainage basin in the Himalayan region. The major geomorphic features observed are fill-cut and strath terraces, alluvial fans, landslides, small talus cones and debris-flow deposits. The slopes range from 4° to 41° and have been divided into seven classes consisting of 6° intervals each. Lithologically, the area consists of phyllite, quartzite, slate, limestone, conglomerate and granite. An erosion intensity map of this region indicates that most of the high erosion areas lie close to the main river and their distribution is controlled mainly by the recent drift material and the valleyside slopes.

Although this method is qualitative, it can be useful for a preliminary evaluation of erosion intensity. and for delimiting high erosion areas for environmental planning.