Research On The Function Of The Water Conservation And The Soil Protection Of Forest In The Three-Gorges Area, Yangtze River

Forest is the main part of the earth, and it is also the active factors to prevent soil and water loss. Based on the mechanism of the Soil and water conservation function of forest of the main forest in the Three Gorges, the soil and water function of different forest were analyzed. The effects of land utilization change on runoff and sediment in small watershed were simulated.On slope scale, hydrological function mechanism of typical forest communities were investigated and evaluated based on the quantitative analysis in hydrological effects of soil layers and slope runoff characteristics in the 14 rainfalls conditions by the methods of modeling, statistical method, PCA (principal component analysis), and so on. The water holding capacity is different in each soil layer and the water capacity in shallow soil layers were bigger than that in deep soil layers. The sequence steady infiltration rate of different stands is evergreen broadleaf shrub forest(10.169 mm/min)> Phyllostachys pubescence forest (0.927 mm/min)>mixed Pinus massoniana-deciduous forest (0.743 mm/min) > evergreen broadleaf forest (0.551 mm/min) . The primary surface runoff duration of evergreen broadleaf shrub forest was the longest(2.37h), and then evergreen broadleaf forest (2.11h) , and that of mixed Pinus massoniana-deciduous forest was the shortest (1.41h) . Everage surface runoff duration of mixed Pinus massoniana-deciduous forest was the longest (31.63h), and evergreen broadleaf forest was the shortest(25.21h). Forest has obvious function to decrease flood peak, and the effect of evergreen broadleaf shrub forest was the biggest, and the Phyllostachys pubescence forest has the smallest effect.The coordinative comprehensive evaluation method was used to evaluate the soil and water conservation function of different forest. The results showed that evergreen broadleaf shrub forest has the biggest capability to prevent soil and water loss(0.0653), and mixed Pinus massoniana-deciduous forest is the second(1.7835), and then is the evergreen broadleaf forest (2.1877)and the Phyllostachyspubescence forest(2.5718).The analysisi of change of forest and runoff and sediment in Xiangxihe watershed showed that annual runoff depth was negatively correlated to forest cover rate, runoff depth will increase by 17.5 mm if forest cover decreases by 1%. And scanty runoff depth will decrease by 0.13 mm if forest volume decreases by 104 m~3. At the same time, ratio of peak discharge to low flow will increase by 0.3 if forest cover decreases by 1%. Annual sediment delivery modulus is negatively correlated to forest change.