The effect of drying-Wetting cycles to the Wischmeier soil erodibility factors

Abstract

Soil erodibility is almost always determined and regarded as a constant parameter that does not change with the climate change. Indonesia has dry and wet seasons which may greatly affected the soil properties. Most erosion models and sediment prediction have been developed based on the soil erodibility factor (K) determined from Wischmeier Nomograph; although soil physical changes due to drying and wetting cycles were neglected. This paper presents the Weischmeier soil erodibility factors affected by the soil properties' change on the drying and wetting cycles. For this particular purpose, the effect of drying-wetting cycle's repetition on undisturbed soil from Manting Basin Mojokerto had been studied. The drying-wetting cycle's processes were repeated 6 times; the properties of the soil specimens were investigated at 1, 2, 4 and 6 cycle. During the drying process, the soil specimens were naturally and gradually air dried; while in the wetting process, the soil specimens were gradually wetted up to their fully saturated condition. The soil properties such as: water content (wc), degree of saturation (Sr), void ratio (e), suction and dry unit weight were measured at every desired conditions. The Weischmeier soil erodibility factors were then determined using Weischmeier Nomograph. The results showed that the soil erodibility factors were almost insignificantly unchanged on the dry condition up to around 90% degree of saturation; but then they were decreased rapidly up to 100% degree of saturation. This is thought to be due that the permeability coefficient greatly increase at nearly saturated condition; this condition change the permeability level from very slow to slow to moderate in the Weischmeier Nomograph.