EROSION MODELLING AND SOIL LOSS PREDICTION UNDER CHANGING LAND USE FOR A CATCHMENT ON MAURITIUS

ABSTRACT

Sugarcane is the dominant form of agriculture on the island of Mauritius but the industry is facing increasing financial constraints that will probably lead to greater diversity in agriculture. Although sugarcane is considered a soil conservation crop, little is known of the current erosion rates on the island and the effect of changing crop types on sediment yields. Modelling of the potential soil loss in the Rivierre Des Anguilles, a southern catchment on Mauritius, was undertaken to obtain an understanding of the extent to which soil erosion is affected by different land use. Two erosion models are applied within a GIS framework: the Revised Universal Soil Loss Equation (RUSLE) and the Soil Loss Estimation Model of Southern Africa (SLEMSA). RUSLE is further used to predict soil loss for the catchment under three potential crop diversification scenarios. Although soil loss ranges considerably, model outputs show a similar trend in mean soil loss rates between the cropping systems in the catchment. Rates are generally highest on steep slopes (>20%) with high annual rainfall (2 400mm) along the river and in the upper catchment area. Predicted soil loss results indicate a strong inverse relationship with vegetation cover; infrequently disturbed land use types such as natural vegetation, tea and banana plantations have low soil loss values (1 to 4 t.ha⁻¹.yr⁻¹), whereas frequently disturbed land use types such as intercropped cane and vegetables have moderate (13 t.ha⁻¹.yr⁻¹) to very high (80 t.ha⁻¹.yr⁻¹) soil loss rates. Results show that land use change to pineapple and vegetables will have a considerable influence on soil erosion with mean soil loss for the catchment doubling and quadrupling respectively. Such crops should be confined to low slope angles and be supported by soil management practices.