The Influence Of Vegetation Change On Hydrologic Factor In Nanxiaohegou

Vegetation structure is an important measure to control soil and water loss and to improve ecological environment. So the study on eco-hydrological effects of vegetation structure/change has great practical significance.Based on the data measured from different runoff plot in Yangjiagou and Nanxiaohegou watershed and refer to a large amount of documents, the aquatic environment effects of man's activity and vegetation change in watershed are generally analyzed by the methods of pairing, quantization and modeling. The main findings of this study are as fallows:1. Based on the measured date of Yangjiagou watershed, the yearly average benefit of dammed up runoff is 57.9% by comparing with Dongzhuanggou, the dammed up sediment is 81.3%. Through comparing and pairing runoff yield and sediment yield with the every period, the increase water quantity which is influenced by man's activity accounting to 45.13% before the harnessing; the reduced yearly average sediment accounting to 10.9% before the harnessing. In flood season, the influence of different vegetation change on the runoff, the sediment, the raindrop energy and the erosion resistance have been analyzed, and have established empirical relationships, along with vegetation increase, the runoff and the sediment decrease; the benefit of impoundment and sediment trapping increasing.2. The impacts of vegetation change of small watershed in loess gulley area on yearly runoff and sediment are analyzed by parallel observation in the comparable watershed and by historic date in one watershed. With the increase of vegetation coverage the runoff and the sediment decrease. The relationship of runoff in flood season is analyzed at the same rainfall, the result of runoff coefficient shows: the runoff and sediment yield of farmland is the biggest.3. The impacts of vegetation change of different runoff plot on the soil moisture content are analyzed, the identical vegetation, the soil moisture content increase with increase of antecedent rainfall amount , at the same time also came under the rain strong influence; The soil moisture content reduce with soil increase of layer depth.4.The BP neural network is applied in Yangjiagou to simulate and predict the runoff and the sediment yield, based on the date of rainfall, and the simulation results is good; The BP neural network is applied indifferent runoff plot to simulate and predict the runoff generation and the sediment yield, based on the date of rainfall, the most heavy rain intensity in a short duration, the soil moisture content before raining and the vegetation coverage from the 1978 to 1984, the result meets the general practical requirements.