Lanslides distribution and geological enviroment in main towns of Three-Gorge China

Take 1:10,000 ortho-image made from 1:50,000 aerophoto taken in 2003-03 as the remote sensing data, and digital 1:10,000 topography map as the geographic coordinate control, by using ldquodigital landsliderdquo technique the basic information on distribution and developing geological environment of 826 landslides, each area larger than 1000 m², in the eight study area in front half part of Three Gorge Reservoir of Yangtze River China have been obtained.The landslide distribution density is very different for each area that it is only 1.6%o in the head part of Three Gorge Reservoir and it reached 8% and 7.6% in Badong and Fengjie area. The back and front edge of the landslide body in all of the study area is in the limitation of 970-65 m above sea level. The highest elevation for each landslide distribution is corresponding to the hypsography of the region, and the lowest to the river erosion level. Over 80% landslide in the area distribute in the elevation of 100-400 m above sea level where human being activities frequency. The study revealed that the litho-logy stratum is the most important factor of geological environment for controlling landslide distribution, and "Easy Sliding "index-ES and "Regional Easy Sliding "index-RES are proposed for illustrate the capacity for developing landslide of each litho-logy stratum and the middle Triassic Badong Group clay-limestone, sand and shale inter-bedding- T₂b and middle Jurassic Shaximiao Group clay, sand stone inter-bedding-J₂s are two most important strata for landslide developing. Fold is the major tectonic form of the study area. While the strike line of the fold is parallel to the river, the most landslides developed in the consequent slope, especially near the fold axes. While the folds strike cross the river it has no obvious effect for controlling landslide developing. River Erosion is the important factor for induce the landslides which activities will more frequency and enhanced- after the water storage completed for Three Gorge Reservoir and water level rise from 65-100 m above sea level to 175 m.