GEOGRAPHICAL RESEARCH ›› 2006, Vol. 25 ›› Issue (1): 71-78.

• Earth Surface Processes •

### Rate estimation of geomorphic process of the slope in the reservoir area of Three Gorges Project

HAN Zhi-yong, LI Xu-sheng, XU Qin-mian, CHEN Ke-feng, YANG Da-yuan

1. Department of Urban and Resources Sciences,Nanjing University,Nanjing 210093,China
• Received:2005-04-08 Revised:2005-08-25 Online:2006-02-15 Published:2006-02-15

Abstract:

In the area of Three Gorges,two slope types,namely the deep weathering slope and the colluvium-debris slope,are identified according to our field survey from Fengjie to Badong.Deposits on the deep weathering slope are mainly composed of eluvial materials,and the shallow layer landslide is probably one of the forms of deposit accumulation on the lower part of the slope.The colluvium-debris slope is characteristic of the occurrence of escarpment on the upper part of the slope.Deposits here can be treated as the assemblage of two end members,i.e.,the collapsed block mass and fine slopewash.The amount of the collapsed blocks decreases downslope,while the slopewash layer thickens gradually.The poor stability of deposits on these two types of slopes is revealed by the high rate of denudation and accumulation.The depositing rate can be roughly estimated by dividing total thickness by the deposition age.However,this approach is complicated by the lack of reliable dating of the slopewash.Since the thermoluminescence signals of the slopewash are not completely bleached when deposition,the measured ages can only be treated as the maximum ages in general.As a result,the activity period of the shallow layer landslide on the deep weathering slope is evaluated to be about 1.5ka,the corresponding deposition rate is about 33cm/ka.The main period of the collapse of escarpment is 40ka60ka,and the deposition rate on the middle part of the colluvium-debris slope is approximately 4cm/ka.The distorted trees are often found on this type of slopes.The distortion is caused by deposit creeping,and the distortion extent is an indicator of the creeping rate.The considerable high creeping rate is the denudation rate on the middle part of the slope,as well as the rate of detritus supply to the lower part of the slope.This shows the denudation rate and the deposition rate vary greatly from one place to another place.Although the periodicity of earthy landslide based on the deposition rate cannot be directly derived from this study,we still believe the deposition process controls the occurrence of the earthy landslide to some extent.According to these findings,we assume that efforts of putting an earthy landslide under control should pay attention to the deposition rate in the areas of being prone to slide.These findings should also be taken into consideration when we attempt to prevent soil erosion.