Evaluation Model on Increase Coefficient of Degree of Risk about Debris Flow Ditches after the Wenchuan Earthquake

The Wenchuan Earthquake has not only induced a great deal of collapse and landslide immediately, but also reduced intensity of rock and soil mass in drainage basin, which makes them more liable to be eroded, so that abundant solid matter is provided for formation of debris flow. Activity of debris flow is frequent in disaster area after the earthquake, and great losses have been caused. Evaluation on degree of risk of debris flow ditches is necessary condition for post-disaster reconstruction. Research of evaluation on fatalness of debris flow has acquired quiet great progress at present, and is applied extensively in practice of disaster prevention and reduction. However, rock and soil mass caused by earthquake becomes more incompact, features of barrier dam shaped by earthquake are difficult to be expressed by routine parameter, consequently method for evaluation on degree of risk of debris flow established under general conditions is confined in application of evaluation of degree of risk of debris flow in disaster area after the earthquake. Three important parameters i.e. increment of solid matter after earthquake, seismic intensity and scale of barrier dam are selected in this paper, and evaluation method on increase coefficient of degree of risk of debris flow is put forward after earthquake based on design flow of debris flow. By validation of calculation of 9 typical debris flow ditches in disaster area, increase of degree of risk of debris flow in May 12th disaster area after earthquake can be assessed by this new method rapidly and precisely.