Experimental Verification of the Effect of Slope and Land Use on SCS Runoff Curve Number

The present study investigates experimentally the effect of watershed (i.e. field plot of 22 m × 5 m) slope on rainfall-generated runoff and, in turn, the runoff curve numbers (CN) resulting from field plots (with land use of maize and sugarcane on the soil falling in Hydrologic Soil Group C) located in Roorkee, (India). The results indicated that the plot of 5 % slope yielded the largest runoff and, in turn, CN compared to those due to the plots of 3 and 1 % grades, for the same rainfall, soil, and land use. The CN derived from the present study were quite close to the NEH-4 CN-values, indicating satisfactory match between the two. The use of slope adjusted CN-values in the standard CN method significantly (at 5 % level) improved the otherwise underestimated large runoff events, i.e. model efficiency E improved from 0.47 to 0.78, and R² from 0.71 to 0.83.