长江三峡香溪—莲沱段水土流失的研究

A STUDY ON WATER LOSS AND SOLL EROSION IN XIANGXI——LIANTUO REACH OF THREE GORGES OF THE CHANGJIANG RIVER

长江三峡香溪—莲沱段的水土流失可分为水蚀与重力侵蚀两类。据诸多自然地理因素的定量指标与产沙模数的关系,建立了产沙模数的经验公式[即式(1)],用式(1)计算出区内产沙量。据历史记载资料与地质地貌调查,探讨了区内新滩与链子崖的巨型崩塌-滑坡的成因与发展。在此基础上,研究了区内水土流失对自然环境及三峡工程的影响。

Xiangxi-Liantuo Reach of Three Gorges of the Changjiang River,with a length A8km,has a total watershed area of 3812km2,it belonging to mountain region. According to regional geologic and physiographic characteristics, water loss and soil erosion can be divided into two patterns, namely,water erosion and gravitational erosion.The main physiographic factors affecting water erosion are thickness of weatering crust(T m), runoff depth (R,m/y), dissected density of valley and gullies (D, km/km2) , rate of forest cover(P,%), etc. Then on the basis of the relationship between their quantitative indices and sediment yield modulus(As,t/km2Xy )using the Least Square Method,an equationCl) is set up to calculate sediment yield,it is calculated that sediment yield is 4. 628 ×108t/y of which the bed load takes up 83. 1% of total.Because forest was denuded,rate of forest cover has been decreased from 45. 1% In 1956 to 21. 7% in 1980,thus causing water loss and soil erosion sediment yield increased 47. 0% than in 1956.Gravitational erosion is namely.rock fall and landslide. Huge rock fall and landslide lies in the Xintan of Three Gorges. A huge slip occurred in June 12, 1985,the volume of slumped mass amount to 18. 91×10m3. According to the historical records,since A. D. 377 there have been four times huge rock fall and landslide occerred at Xintan and Lianziyan,brought about,development of water loss and soil erosion.This regional environment deteriorate with, increasing aggradation of the river bed and valley plain,and the outward expansion of stony and rugged land.