REVISITING THE KIRPICH FORMULA USING RAINFALL SIMULATOR EXPERIMENTS

Abstract

In this study, experimental investigation of overland flow time parameters was carried out at varying surface slopes (0.5% to 3%), antecedent soil moisture (8% to 28%) and rainfall intensity (45mm/hr to 90mm/hr). Thirty five experiments were conducted using Advanced Hydrologic System (Rainfall simulator) by generating rainfall on an overland flow plane of area 2 m2 (2m x 1m). A regression analysis was conducted to develop model for determining the time of concentration. It has been found that majority of the existing empirical models available in the literature under-predict the time of concentration. Specifically, this study showed that the Kirpich equation under-predicted the time of concentration by 10 times. This variation can be attributed to the fact that different models were developed under different conditions. Further, these empirical models are based on different definitions of time of concentration. Results further reveals that Kirpich has given high significance to the slope parameter whereas this study showed that the slope is the least significant parameter. Also the existing models available in the literature do not contain antecedent soil moisture (θ) parameter which has a significant role to play in determining the time of concentration. Models such as Mathur and Perumal (2007) and Izzard (1946) were showing good results at low values of antecedent soil moisture content as compared with the observed data of this study.