黄河中游重蚀区不同下垫面的水沙效应

EFFECT OF VARIOUS LAND SURFACES ON RUNOFF AND SEDIMENT YIELD IN THE HEAVY EROSION AREA,THE MIDDLE YELLOW RIVER

通过大量野外工作,对研究区降水、径流和输沙作了系统分析,揭示了黄土、风沙和基岩等不同下垫面的水沙效应,加深了对水沙过程强度大、集中、时空多变等特点的认识,为预测灾变性雨洪的水沙效应提供了科学依居。

Located in loess plateau of China, the study area belongs to dry and semi-arid region with 12. 95 X 104knV of area. Here erosion is very heavy. It is the main source area causing channel deposition in the lower Yellow River. By a detailed analysis on characteristics of precipitation-runoff-sediment yield of various land surfaces of the area, the main points of the paper are as follows :1. Annual precipitation in the area is generally 450 mm or so. of which rainfall from June to Sept.amounts to 73 per cent of the total.Here not only is storm intensity very heavy as that a heavy storm on Aug. 1,1997. in which the maximum point rainfall of the storm centre amounted to 1 400 mm with 10 hours duration, but the storms are frequent in summer and varied in time and space.2. Surface material compositions of the area are mainly loess (62%). sand blown by the wind (24%) and bed rock (\4%).Various surfaces make a notable impact on runoff and sedi-ment runoff processes.Of mean annual runoff, only 18- 7 per cent is in the form of baseflow for the rock outcrop area.50?0 per cent for the area covered with loess, and more than 90 per cent for the area covered with sand blown by the wind. Of mean annual runoff, about 85 per cent occurs from June to Sept. for the rock area, about 65 per cent for the loess area; and 35 per cent for the area covered with sand. As to mean annual sediment yield, of which over 97 per cent falls in flood period for the rock area, about 85~97 per cent for the loess area and only 30 ?55 per cent for the area covered with sand.3. Both material composition and form structure of land surface have a great influence on erosion intensity. In sandstone area with very weak resistance to erosion the breaching extents (A.. I A) of the surface, the quotient of the gully or valley cumulative area (A,,) and the total drainage area (A), typically lie in the range 0. 4 to 0. 7 and the sediment yield module highly reach the range between 20 000 t/km' ?a and 21 000 t/knv ?a.The module generally lie in the range 10 000 t/km ?a to 18 000 t/km' ?a for loess mantle area with the values of A, IA lying between 0. 25 and 0. 48.The module often lie between 200 t/km2 ?a and 400 t/knv ?a for the sand mantle area with the values of A,,/A lying between 0. 03 to 0. 05. As to within the loess mantle area the values of erosion modulus may be from 3 to 4 times variation between various sections due to difference in morphology.