Soil Water Migration & Entironment Effect In Shenfu-Dongsheng Subsidence Area

Shenfu-Dongsheng mining area is located in the arid and semi-arid region of northwest of China, with frangible entironment and deficient water resources. With the durative development of coal mine resources, it made the ground collapsing extensively and ground water level decreasing to a large extent and the geological and entironmental problem is increasingly prominent. How to use soil water resources reasonably and efficiently is highly important for physiological water requirement of vegetation and entironmental reconstruction of subsidence area. In consideration of the entironment reconstruction in Shendfu-Dongsheng subsidence area, soil water of mining area, as a limiting factor of entironment reconstruction, is focused on. Using geologic survey, physical simulation in laboratory, in situ field experiments and field measurement, this paper researches the migration of soil water and entironment effect in Shenfu-Dongsheng subsidence area. The main results are as follows:(1) In unsteady phase, ground fissures caused by collapsing facilitate the loss of soil water. The soil water content of fissure district is about 50% less than that of non-fissure district of subsidence area, which close to or below wilting coefficient. This will be a great threat for the survival and growth of vegetation.(2) Contrast to non-subsidence area, the steady subsidence area has stronger ability to accept precipitation, which can be concluded from the truth that soil water content of steady subsidence area is apparently larger than that of non-subsidence area. This will be helpful to the entironment reconstruction of subsidence area. But in dry spring, the steady subsidence area has a lower water-storing capacity in shallow layer (above 30cm) than that of non- subsidence area, which will be a disadvantage for the budding of short-root vegetation.(3) In steady phase, fissures in shallow layer of unsaturated zone are filled up, but some hidden fissures are still exist in middle and deep layer, which are no use for transmitting water in unsaturated condition. Thus, we used pore structure instead of pore-fissure structure in the simulation of soil water migration in steady phase.(4) In the condition of constant rainfall intensity, the process of wetting front moving in fine sand and coarse sand can be divided into two phases. In the first phase (i.e. during rainfall), the depth of wetting front is linear with rainfall time. In the second phase (i.e. after rainfall or the course of soil water redistribution), power function works. Migration velocity of infiltration water is an exponential decline with depth. It shows that the recharge of groundwater by rainfall needs a very long time in the condition of thick unsaturated zone in steady phase.