Dynamic Characteristics And Analogue Simulation Of Shallow Groundwater For Hedong Irrigation District In Ningxia

The study of groundwater dynamic is an effective way to awareness of groundwater resources in the formation, evolution and reveals the internal state characteristics of the groundwater system. Hedong Irrigation District in Ningxia Hui Autonomous Region is situated in the northwest of China, a typical irrigation area of arid region. Eco-environment issues caused by long-term irrigation have become a restraining factor for social and economic development. In order to address the problem of regional groundwater, exploit reasonably and manage the groundwater resources, it is important to study the regional groundwater regime, understand the dynamic characteristics of groundwater, simulation and forecast groundwater dynamic.In this paper, the author analyzed the structure of groundwater aquifer, characteristics of recharge, runoff and discharge, combined with field survey and second-hand data. Based on long-term monitoring data, the groundwater dynamic and influencing factors were analyzed, and groundwater balance in target area was calculated. Supported by GIS technology, the fractal dimension of groundwater level on different time scale was calculated. Then the spatial variability of groundwater level was analyzed using geostatistics method, and the different period of groundwater level maps were made by ordinary Kriging interpolation. In MATLAB platform, the BP-ANN groundwater dynamic simulation model was established and used to predict the groundwater table under the different scenario. The main conclusions were summarized as follows:(1)General Characteristics of Groundwater DynamicThe dynamic type of shallow groundwater in Hedong Irrigation District is irrigation-evaporation. Due to the effect of irrigation, the change of groundwater level in distinct zone exist obvious periodicity, which steady in inter-annual and fluctuate largely in one year. Man-made factors such as diverted water volume and displacement are the main influence factors for groundwater dynamic. Meteorological factors such as precipitation, temperature, sunshine hours distributed unevenly in area and time, and its affect on groundwater level are distinct in different areas. In Hedong Irrigation District, groundwater dynamic is proper equilibrium during equilibrium period, the relatively balanced deviation is1.04%, and in a state of equilibrium basically.(2)Fractal Characteristics and Spatial Variation of Groundwater LevelFractal dimension of inter-annual groundwater level hydrograph in Hedong Irrigation District was between1and1.1, and it was close to1for the year, which indicated the level of distribution of groundwater irregularities and complexity were small in time and space. The complexity of groundwater dynamic process was difference in unlike regions, but the changes were not severe on the whole.There was a normal distribution of groundwater level sample in Hedong Irrigation District was obviously U trends in the east-west direction, and direction of stable linear trend in the north-south. The result of variability analysis showed that the structural factors influenced on the spatial variability of groundwater level were weakening, and human activities such as irrigation, groundwater exploitation were strengthening. Groundwater level had a strong spatial correlation and the more groundwater depth was shallow, the more correlation was enhanced. Spatial correlation that in natural state was small that was remarkable increased by irrigation. Ordinary Kringing interpolation showed that the inter-annual change of groundwater level was small and was comparatively large for the year in Hedong Irrigation District.(3)Simulation and Prediction of Groundwater DynamicSimulation model of BP-ANN on groundwater dynamic with high generalization capability reflected the characteristics of change about groundwater level dynamic comprehensively, which could be used to predict the change of groundwater dynamic in Hedong Irrigation District. The results of model prediction showed that groundwater level significantly dropped when diverted water volume reduced and sunshine hours increased, but the effect of increase on sunshine hours was more remarkable than increase of diverted water volume. When diverted water volume increased and sunshine hours reduced, groundwater level was significantly increased but the influence of rise range of groundwater level on increase of diverted water volume was much higher than that sunshine hours. It was obvious that diverted water volume had a function of recharge on shallow groundwater in Hedong Irrigation District, which in the future diverted water volume sharply cut would have a directly influence on the groundwater depth. Therefore, to implement the conversion of water rights and water-saving transformation process continually in the future, the effect of diverted water volume to groundwater recharge should be given full consideration, and it is appropriate that diverted water volume from Yellow River keeping in900million m3can ensure appropriate groundwater depth.