Taking an abandoned quarry watershed in Beijing City as the research object

the parameters of watershed and landform were extracted and analyzed using the raster DEM at the different resolutions from 0.3to 7 m.Results showed that the morphological structure of drainage networks extracted from the different resolution DEMs had significant differences.The structures of drainage networks had significant differences between the two sets of gird size:one was with 7

4and 3mand the other was with 2

1

0.7

0.5

0.4and 0.3m.Positions of the two main channels changed dramatically.But there was no marked qualitative difference among drainage area

channel length and gradient

average slope and elevation.The difference was obvious between the total channel length and drainage density.According to the results

the optimal resolution of DEM was estimated to be 0.5m.The main components

i.e.

elevation and slope

were obtained using the PCA(principal component analysis).By se tting four runoff plots of 20°

25°

30°and 35°in the research area

the relationships among rainfall

slope

runoff and soil erosion were analyzed and obtained.Then

the average runoff and soil erosion of the whole drainage basin were computed for different slope grades and rainfall levels.The research results can provide reference for the restoration and ecological reconstruction of abandoned quarry.