Experimental Study on Effects of Plot Length on Runoff Depth Under Natural Precipitation

This paper focuses on the experimental study to determine the relationship of slope length on runoff depth and runoff coefficient. Based on the thorough review of different plot sizes (lengths) for soil loss estimation, the slope of the current experimental plots was designed with an angle of 22.78° from horizontal. The plots were grouped into Plot A (1 m wide x 1 m slope long), Plot B (1 m wide x 2 m slope long) and Plot C (1 m wide x 3 m slope long). Homogenous soil samples were used for all the 3 experimental plots and a tipping bucket rain gauge with automatic data logger was installed at the experimental plot for rainfall intensities collection for the individual rainfall events. Runoff volumes were recorded for the individual rainfall events for determination of runoff coefficients. The rainfall intensities are grouped into ⩽30 mm/h, 30-60 mm/h and ⩾60 mm/h. It was found that the shorter plot (Plot A) has the highest runoff coefficients of 96.34%, 69.89% and 96.26% for 3 different precipitation groups ⩽30 mm/h, 30-60 mm/h and ⩾60 mm/h, respectively. Based on results, the longest plot (Plot C) shows that an increase in mean values of 33.59%, 38.30% and 49.45% as the intensity increased from ⩽30 mm/h to ⩾60 mm/h. From this study, it can be concluded that comparatively longer slope length tends to result in lower runoff depth.