The Quantity Of The Water Requirements For The Ecological Environment Of The Typical Small Watershed Of The North Shaanxi Loess Plateau

Aimed at the current problems of the ecological protection and the water resource collocation for the ecological environment occurring in the North Shaanxi Loess Plateau, the quantity of water requirement for the ecological environment in the Liudaogao watershed, which locates in the center of the water-wind overlapped erosion region and is typical of the Loess Plateau, is analyzed and discussed in order to have more understandings of these problems. In this dissertation, the dynamic variation characteristics of soil water content of different land use patterns, the water-consuming properties of the typical vegetation and the spatio-temporal distribution of the soil water in the watershed are studied through the field observation and measurement of the soil water content of standard runoff plots and fixed sampling locations. The quantity of water requirements for the watershed and North Shaanxi Loess Plateau are calculated and discussed by means of the experimental observation of water balance analysis. The main results are as follows.(1) The results obtained by traditional statistical method indicate that the variation extent of the soil infiltration properties of a field slope is medium and the geo-statistical method shows the similar result to this. The variation extent of the soil bulk density is weak and that of the capillary moisture content and saturated moisture content is medium in the catchment. When using the geo-statistical method, the semi-variance variograms of these parameters are both floating and other approaches may be needed to have a deeper insigh.(2) The vertical change of soil water in the profile is obviously different in layers. Based on the standard deviation and variation coefficient, the soil water change of natural grassland plot can be divided into four layers and that of the soybean plot, the millet plot, the returned grassland plot from farming and the Caragana Korshinskii plot can be divided into three layers by cluster analysis.(3) The temporal dynamic change tendency of water-storage capacity of the five land use patterns is accordant with that of natural rainfall, the moisture circulation processes of the five land use patterns nearly were all "compensation-consumption- compensation". The sort order of the evapo-transpiration within the observation period is Caragana Korshinskii, natural grassland, de-farming grassland, soybean, and millet, and that of total runoff produced in each runoff plot within the observation period is soybean, millet, de-farming grassland, natural grassland, and Caragana Korshinskii; For the Caragana Korshinskii and natural grassland, their transpiration and evaporation capacity are the maximum while their total runoff is the minimum, which shows that its efficiency of water application is high and they have better effects for the soil and water conservation.(4) Different site types influence the soil water content obviously. For the diverse location of slope, the soil water content at the slope bottoms is generally higher than that at the slope tops. For the different slope azimuth, the soil water of the shady slope is always higher than that of the sunny slope, however, if there are great differences among the vegetation, the soil texture, the original water content and other factors, the soil water of the shady slope is no higher than that of the sunny slope. For the various topographies, the sort order of the average soil water is dam land, shallow channel, the top ofloess hill, and the gully channel.(5) The rainfall distribution in the watershed shows certain unsteadiness in the temporal distribution, the rainfall which happens in the flood season takes a percentage of above 67% of the total rainfall in the observation period. The ground runoff mainly produces in the flood season, and the total ground runoff in the No.1 catchment, No. 2 catchment and the whole watershed is 9160, 6772, and 18384 m3 respectively, with the corresponding runoff depth being 35.67, 13.11, and 44.93mm, the water-storage capacity in them all decrease, and their tota...