Proposing an Empirical Equation for Estimation of the Sediment Concentration of Debris Flow (Case Study: Jiangjia Gully in China)

Debris flow, as a severe geological disaster, causes huge damages in the mountainous areas every year. The peak discharge of flood and the hydraulic roughness of flow are affected by sediment concentration of debris flow. Therefore, the estimation of sediment concentration based on physical characteristics of basin, sediment and precipitation are necessary. The aim of this study is proposing an empirical equation for the determination of the sediment concentration of the debris flows in the study area using the rainfall parameters, so that the weakness of applying the fixed value for the debris flow concentration proposed by previous researchers can be removed. For this purpose, the relations between each of the parameters including cumulative rainfall, antecedent rainfall and the total rainfall (sum of cumulative and antecedent rainfalls) parameters with sediment concentration of the debris flows were investigated by using of the rainfall and the debris flow density recorded in the international research station, Jiangjia Gully, for the period of 1999-2004 years. To derive the best equation, cross validation method was used and the relations error were determined by statistical indicators including coefficient of determination, R2, Mean Absolute Relative Error (MARE) and Nash-Sutcliffe Efficiency (NSE) coefficient. Results showed that higher correctness was obtained using the sum of cumulative rainfall and antecedent rainfall parameters (total rainfall) for determining of the sediment concentration of debris flow. The statistical indices of the proposed model (MARE=0.06, R2=0.86 and NSE=0.84) represent the high ability of the proposed equation in the estimation of the sediment concentration of debris flows where the estimation error of the sediment concentration was reduced on average about 80% comparing to other researchers’ equations. The range of the relative density of sediment is between 1.63-2.23 gr/cm3. Moreover, the range for the cumulative rainfall and the antecedent rainfall are varied between 3.36-75.36 and 0.772-92.59 mm, respectively. After calibration of the proposed equation of this research, it can be used for estimation of the sediment concentration of debris flow in the other prone basins, which have the similar storms.