Study On Permeability Coefficient's Evolvement In Wei Bei Loess Tableland Irrigation Area

With the development of irrigation engineering, agricultural water conditions of Wei bei loess tableland has got great improvement. Its agricultural production and economic development had increased promptly. At the same time, its natural ecological environment, geological condition and hydro-geological conditions had changed enormously as the water riching. All these were because of the special structural characteristic of loess.The space system of the loess is a complicated system which connected by small opening, hole and cranny. The loess of different time and dissimilar burying depth had different crevice system characteristics. These not only caused the permeability and water characteristic of loess increasing when its burying depth reduced, but also caused the permeability of identical epoch loess have differences in the horizontal direction, and its characteristics have aeolotropy in the vertical and horizontal direction .The differences of the loess aquifer and the other rocks were the loess aquifer's interspaces and hydraulic properties were variable, which determined by the solubility of the loess. Under irrigation condition, the filter water should happen a series of physics and chemical action constantly when it filtered in the aerated zone and motioned in the aquifer, the interspace was transformed by the corrosion constantly. It showed that the hydro-geological parameter of the loess is not a fixed number, it evolved with hydro-geological conditions constantly. Therefore, studying the hydro-geological parameter (the quota target of stratum's water-bearing attribute) had largely significance.The papper made a series of permeated simulated test, approved the permeability coefficient's evolvement rules of the loess aquifer. The rules were showed as follows:(1)Under a certain fixed water stress, the permeability coefficient of the loess aquifer should be augment with the salinity of supply water's reducing.(2)Under a certain fixed salinity, the permeability coefficient of the loess aquifer should be augment with the salinity of supply water's increasing.(3)Under the influences of water stress and salinity, the permeability coefficient of the loess aquifer should be varied regularly with the water stress's increasing.The paper had drawn the conclusion through the analysis as follows:(1)The new aquifer's forming was because of Longly irrigating in Wei bei loess tableland. In this area, irrigation and rains supplied groundwater supplementary and their intensify enhanced mutually, thus irrigation water had obvious permeability.(2)The infiltrated water should happen a series of physics and chemical action constantly when it filtered in the aerated zone of aquifer.The irrigation water had less quality than the rain water, thus caused the hardness index of ground water enlarged.(3)After undergoed long-time irrigation, the hydro-geological conditions of Wei bei loess tableland had changed at all. The hydraulic properties of loess had great changed,its hydro-geological parameter should be very considerable(as compared the natural condition).