Modified runoff curve numbers for bare crust forming sandy soils

Abstract

Runoff curve numbers (CN) for bare crust-forming sandy soils in the Indian Arid Zone were derived from rainfall and runoff data recorded over a period of 7 years from 1975 to 1981. Contrary to the Soil Conservation Service (SCS) handbook value of 77, the actual optimized CN for 0.5% and 5-10% slopes were found to be 87 and 91, respectively, indicating a greater volume of generated runoff from these soils than estimated by the SCS method. The handbook CN value underpredicted runoff by 47-68% for storms >100 mm and 163-400% for storms <25 mm. A significant correlation (r = 0.898, n = 227) was found between the observed and predicted values using a modified CN based on the measurements.