A hydrology-process based method for correlating debris flow density to rainfall parameters and its application on debris flow prediction

Abstract

Antecedent effective rainfall (Ar) and rainfall intensity (I) play an important role in the formation process of debris flow. Establishing Ar-I threshold curve of debris flow is hence of great importance for early warning purpose. However, conventional statistical models require sufficient observation data, which is not feasible for developing countries without adequate field observation stations. To this end, a hydrology-process based method is proposed to construct the Ar-I threshold. In this model, debris flow is considered as a soil-water mixture composed of solid and water, the loose solid sources contributing to debris flow is provided by the rainfall-induced shallow landslide, and the water is from rainfall-induced runoff. A necessity of having the characteristics of debris flow is that the density of water-soil mixture should approximate to the density of debris flow ranging from 1.2 to 2.3 g/cm3. The value of 1.2 and 2.3 g/cm3, which represent lower and upper borders of the density of debris flow, is used as the threshold for predicting debris flow. The task of the model is to find out the rainfall parameters that correlate with the border value of density and use the searched data of rainfall parameters to fit corresponding curves. Verification of the proposed threshold was conducted based on field observation data of Jiangjia Gully located in Yunnan Province, China, which indicates the false negative and false positive rates of the threshold are 26.7% and 15%, respectively. The precision of the threshold is evaluated as 82.6% by the Receiver Operator Characteristics method, which can provide a solution for debris flow early warning.