A PRELIMINARY ANALYSIS OF THE PROCESSES OF SEDIMENT YIELD IN SMALL CATCHMENT ON THE LOESS PLATEAU
黄土高原沟道流域产沙过程的初步分析

The main regions of sediment yield lie on the both sides of Huang He from Hekouzen to Lunmen, and in the upper and middle reaches of Jinhe, Lohe and Wehe river on the Loess Plateau. The sediment yield is concentrated in the period from July to September, or in one or two rainstorms.The delivery ratio approches to in the watersheds on the Plateau. Sediment yield in a small catchment is the result of both physical factors and human activities.Soil erosion is proportional to the addition of precipitation and the depth of runoff and increases with the gradient of the ground surface, while the runoff flow erosion decreases on the slope of over 25°-28°. Clayly loess is present in the south part of the Plateau and coarse loess in the north. Scrub is better for soil conservation than other vegetations. The sediment yield has been increasing in the last 30 years in the lower reaches of the Huanghe. The artificial increase is about 23-35% of the mean transporting sediment.The pattern and intensity of soil erosion vertically change from the top to bottom in the small catchment. Rill erosion dominates in the intergully, and gully bank is an area of multi-functions of water erosion, gravitational and cavern erosions. The sediment output in gully bank is abnut 59% higher that in the Loess region of gullied-hilly, and most sediment yield from the gully bank is in the Loess gullied-table areas.