Impact of Monsoon Rainfall on Soil Erosion

Indrani Pal, Cambridge University, Geotechnical Engineering Group

Abstract

Monsoons are seasons. Monsoon rainfall is a major source of soil erosion. Soil erosion poses a range of significant environmental problems. Sediment, the product of soil erosion, is unique in that it can act, not only as a pollutant itself, but also as a transport medium for other pollutants that may be adsorbed onto soil particles. A practical and direct means of minimising contaminant transport through sediment generation is the stabilisation of the sediment source by controlling soil erosion through the use of proper management practices.

The objective of this study is to estimate rainfall induced soil erosion in Kerala, a region in south-west India, which experiences high monsoon rainfall every year and is home to soils highly susceptible to erosion, using RUSLE2 a computerised erosion model. Emphasis has been placed on rainfall erosivity the climatological factor of RUSLE2 which was determined using a 50-year rainfall data introducing a new methodology and assumptions for disaggregating daily to hourly data to fit into a unit energy model utilised obtaining erosivity estimates. This methodology was validated using north Australian monsoon data and found to be satisfactory. Sensitivity of soil erosion to variations in the model parameters, which apart from erosivity include soil erodibility, slope length, slope steepness and cover-management conditions, was analysed. The results from this study estimate current soil erosion rates for Kerala to be in the order of 19-150 tonne/ha/yr depending on the rainfall fluctuations and other given/assumed parameter conditions which are higher as compared to non-monsoon rainfall erosion of the UK and contaminant movement of 0.23-1.5 tonne/ha from a typical contaminated site. The results also show that a bare soil surface subjected to mechanical disturbance and exposed to high rainfall quantity and intensity is very much vulnerable to erosion and that, systems with vegetative cover and surface mulch applications can reduce soil erosion by as much as 92% thus potentially reducing the environmental damage that could be caused by soil erosion from contaminated land.