Research Of Different Vegetation Types Affect Runoff Process In The Three-Gorges Area Of Yangtze River

In this paper, the main problem was studied on different vegetations affect runoff processs in Three-Gorges of Yangtze River. To select and research on mixed broadleaf-conifer forest, broad-leaved forest, phyllostachys pubescens forest, shrub forest and farmland in Jinyun Mountain in Chongqing. After researching rainfall characteristics, canopy interception, water retention of litter on the slope land and soil infiltration, and analyzing the process of the surface runoff and infiltrated flow in same precipitation. Estimated water and flood regulation in different sort vegetations, the main conclusions were as the following:(1) By the grey system theory, calculated the grey correlation degree of factors influencing canopy interception. Mixed broadleaf-conifer forest had the highest grey correlation degree, it reach 0.87. Broad-leaved forest had approximate grey correlation degree. Precipitation had maximal effect to Phyllostachys pubescens forest, shrub forest and farmland, and the grey correlation degree of precipitation is 0.97, 0.89 and 0.91.(2) In Jinyun Mountain in Chongqing in Three-Gorges area of Yangtze River, the water-holding ability of the litters were shrub forest > mixed broadleaf-conifer forest > broad-leaved forest >phyllostachys pubescens forest. It was greatly change in firstly 2 hours, the water-holding amount of every layer would reach saturation in 8 hours. The water-holding amount of undecomposed layer was less than half-decomposed layer and decomposed layer. Regression analysis indicated that thewater-holding amount of every layer and soaking time had Q = a ln t + b relationship. Litter had fast water absorption speed in the first 2 hours, shrub forest had the fastest water absorption speed, and it reached 22.208 mm·h^-1 Water absorption speed of 4 kinds of vegetations were mixed broadleaf-conifer forest > shrub forest > broad-leaved forest >phyllostachys pubescens forest. The relationship of thewater absorption rate and soaking time was V = ktⁿ.(3) In the same precipitation, the amount of surface runoff of 5 typical vegetations slope land in order was phyllostachys pubescens forest, farmland, mixed broadleaf-conifer forest, shrub forest and broad-leaved forest. The amount of infiltrated flow in order were broad-leaved forest, mixed broadleaf-conifer forest, shrub forest, farmland and phyllostachys pubescens forest. The fore precipitation greatly affected the processes of surface runoff and infiltrated flow. The process of infiltrated flow last time longer than surface runoff, the peak value of curvilinear of infiltrated flow fell slowly. In the same precipitation, broad-leaved forest had the largest ability to control flood among 5 typical vegetations.By contrasting and analyzing the data form the surface runoff and infiltrated flow in the same precipitation, with the same precipitation, the ability of flood control of mixed broadleaf-conifer forest was the second. Shrub forest and farmland had the equivalent effect to control flood. Phyllostachys pubescens forest has the weakest ability of control flood among the 5 typical vegetations. Throughregression analysis on the surface runoff (Q_{地表径流} ) and rainfall ( P) indifferent vegetations slope land,there was cubic equation between surface runoff and rainfall in mixed broadleaf-conifer forest, broad-leaved forest and phyllostachys pubescens forest. There was exponential function between surface runoff and rainfall in shrub forest and farmland.(4) The average soil water holding capacity under 100 centimeter in experimental area in order were shrub forest (131700 t·hm^-2) , mixed broadleaf-conifer forest (116200 t·hm^-2) , phyllostachys pubescens forest (113100t·hm^-2) , broad-leaved forest (95000 t·hm^-2) and farmland (65000t·hm^-2).(5) Based on the grey system theory, and analysed the factors which effected surface runoff coefficient, found out the grey correlation degree of forest crown closure, the largest amount of canopy water holding, shrub and herbage coverage, litter thickness, the most amount water holding capacity of litter, soil non-capillary porosity, soil infiltration rate, soil saturated water holding capacity, etc., were excess of 0.5. Hydrologic function of soil layer had decisive effect whole vegetable system to regulate water and control flood. After analysd the factors of forestry vegetations which regulate water and reduce silt. Established regression model to surface runoff and infiltrated flow in different vegetations. Selected broad-leaved forest and mixed broadleaf-conifer forest as the best vegetation types to regulate water and control flood in Jinyun Mountain in Chongqing.