The Study Of Flat Shape Of Alluvial Fans And The Model For Predicting Deposition Of Debris Flow In Inner Mongolia

Debris flow is one of the most common geological disasters in mountain areas,which occurs every day around the world. Two-thirds of total land areas are mountainareas in China. Accounting for steep terrain of mountain areas, more and more peoplelive on or near the alluvial fans for its flat terrain. Thus the alluvial fans come to bethe main issue of the whole society. It has a great significance to predict thedeposition of debris flow for the sitting of hydroelectric power stations, mitigationstructures, towns and road alignments.According to the site investigation and laboratory testing, the analysis has beenmade of the geological environment and characteristics of debris flows in Chifengpumped storage power station in Inner Mongolia. The parameters K1and K2areestablished based on the study of flat shape of alluvial fans. The equationsrepresenting the relation between the factors of characteristics of debris flow andareas of alluvial fans (S), parameters K1and K2have been made up using thenon-linear regression analysis, which compose the model for predicting the depositionof debris flow. Comparing the model with other four models established early, ananalysis has been made for discussing the advantages and disadvantages. Then therange of deposition of debris flows which’s alluvial fans have been heavily destroyedare predicted with the model. The main conclusions are as follows:The research area is located in the north of China with the temperate monsoonclimate and annual rainfall between400and800mm. Debris flows in the region arealways diluted debris flow with low frequency and the quantity of loose material isnot rich. With the developmental stages in the elderly or termination and mild-prone,their debris-flow activity is weak.The main two kinds of flat shapes of alluvial fans are fan-shaped appearing in the accumulation of debris flows in the south and oval appearing in the accumulation ofdebris flows in the research area. The parameters K1and K2are firstly used forquantitatively describing the shape of alluvial fans, which is different from theprevious qualitatively describtion. While parameters K1represents the ratio of lengthto width of the alluvial fans, parameter K2represents the basis shape of alluvial fans.When parameter K2ranges between0.5and0.67, the alluvial fans tend to befan-shaped. When it ranges between0.67and0.84, the alluvial fans tend to be ovalapproximately.The equation which is composed by the solid mass and density of debris flowand slope of alluvial fans is build up to predict the area of deposition(S). And theequation which is composed by the velocity and density of debris flow and slope ofalluvial fans is build up to predict the parameter K1. While parameter K2rangesbetween0.67and0.84, the model for predicting deposition of debris flows in researcharea has been constructed. The average error of maximum predicted value of lengthand width of alluvial fans is small relatively.Comparing the model with the other four traditional models, it can be concludedthat traditional models are based on One-dimensional features of alluvial fans withneglecting the two-dimensional features or assuming them be a given value. So therewill be a large error between predictions and facts. Accounting for the changes of flatshapes of alluvial fans, the complete deposition of debris flow can be acquired withmodeling the two-dimensional features of alluvial fans.