Analysis Of Eco-hydrological Effects Of Vegetation Change

Vegetation construction is an important policy measure to control soil and water loss and to improve ecological environment. So the study on eco-hydrological effects of vegetation construction/change has great practical significance.Based on the measured data in Xiangyanggou and parallel-contrast watersheds of Wangjiahe with Dangjiachuan and Baozigou with Liugou, respectively, and with large amount of references, the eco-hydrological effects of vegetation change in watershed are generally analyzed by the methods of contrasting and modeling. The main findings of this paper are as follows:1. Based on the measured data of runoff plots and Xiangyanggou watershed from 1996 to 2001, the impacts of vegetation change on runoff yield, sediment yield, runoff forming process and the content of soil water have been analyzed. The results showed that, with the increase of vegetation coverage in watershed: (i)Storm runoff and sediment yields are reduced; (ii)The total flood volume is reduced, the flood duration is prolonged, the peak flow is decreased dramatically, and the flood hydrograph is characterized by the rapid rise and mitigatory recession; (iii)The percentage of ground runoff is increased and the ratio of water source components changed obviously; and (iv)The relative content ofsoil water in 0-100 cm soil layer decreased with the increase of vegetation coverage.2. The impacts of vegetation change of small watershed in loess hilly area on storm runoff and sediment yields and flood process are analyzed by parallel observation in the comparable watersheds and by historic data in one watershed. The results are as follows: the watershed with high vegetation coverage can largely intercept water and sediment, decrease flood peak, lengthen flood process and intensify variation coefficient in storm runoff.3. Based on the data of from many watersheds in different scales and hydrological regions, the eco-hydrological effects of forest change on rainfall interception, runoff regulation, soil erosion, and water quality were comprehensively analysed. The results showed that, with the increase of forest coverage, the rainfall interception, flow in dry season, and runoff uniformity are increased, the peak flow and the ratio of runoff depth in flood season to that in dry season are decreased, the distribution of runoff components changed, the soil erosion is reduced, and the water quality is purified. However, the impacts of forest change on water yield vary greatly among different hydrological regions due to the widespread environmental heterogeneity.4. Considering the vegetation factor, the structural frame of eco-hydrological model was proposed from the point of view of hydrology. At the same time, the 18 storm runoff events happened in Xiangyanggou watershed from 1996 to 1998 are simulated by applying SCS model, and the results showed that the simulation effects is acceptable and the model can meet the general needs.