A sheet erodibility parameter for water erosion modeling in regions with low intensity rain

Soil erodibility reflects the soil effect on the detachment process by rainfall and runoff; an evaluation of this parameter for single storm events was carried out using natural runoff plot data collected for two rainfall seasons in northern Iraq. The region is characterized by a semiarid Mediterranean-type climate with normal rainfall intensity below 20 mm/h and dominant sheet erosion on agricultural land. The plots were three 30 × 3 m and three 10 × 3 m, in fallow, situated on a 6% uniform slope; the soil at the site has a silty clay loam texture and belongs to the Calciorthid suborder. Sheet erosion rate was assumed linearly proportional to the storm power and the sheet flow power; a steady-state turbulent and kinematic sheet flow was also assumed. The results indicated a dominant detachment by rainfall with a substantial variability in storm by storm calculated sheet erodibility. The two-parameter lognormal probability distribution fitted the obtained sheet erodibility values reasonably well. Using this probability distribution, a representative sheet erodibility value of 0.056 × 10⁻³kg/J was obtained for use at the experimental site.