Research On The Formation Condition And Dynamic Of Groundwater In Weibei Loess Mesa Irrigation District

Weibei loess mesa irrigated district locates in the southeast part of loess plateau of China—the middle part of rich Qinchuan. The precipitation of this district is few, whose distribution of space—time is not asymmetry. The constant rate flow of the river here is small, and the rate of the runoff is large. Also in recent years, population increases and agriculture and industry develop fast. All of which make the water problem of this district particularly outstanding. Some areas regard exploiting groundwater in a large amount as a main method of solving water resources shortage, which caused a series of environment problems, and affect the sustainable utilization of the groundwater resources and ecological environment security of the irrigated district seriously. Therefore, study on the formation condition, dynamic types, characteristics and prediction of the groundwater in Weibei loess mesa irrigated district could supply scientific basis for the whole irrigated district's groundwater resources management organization publishing administrative order or technical measure, it also has very important theory meaning and application value to sustainable utilization and constructions of ecological environment of groundwater resources at the same time.On the basis of consulting previous research, this paper summarized and analyzed the geological and geomorphological characteristics, physical structure and hydrolytic weakening properties which had close relations with the formation, storage and migration of groundwater, and illustrated the loess plateau had large room to store groundwater.Groundwater often participates natural water circulation constantly. Proceed from the angle of input, systematic entity and output, the paper discussed supply source of the groundwater through analyzing space—time distribution characteristic of rainfall, natural and artificial surface water (mainly irrigation) and water source supplied from side direction. While the porosity and development characteristics of the loess are the basic conditions which the groundwater could be replenished in the loess area. The discharge forms of groundwater are divided into horizontal and vertical discharge forms. Groundwater dynamic types were analyzed before and after the establishment of the irrigated district, and groundwater dynamic annual and inter-annual variation characteristics of this district were especially discussed. Groundwater system is an open natural and artificial compound system, and contacts closely with human activities, ecological environment and surface water, from which, the paper illustrated the influences of natural factors (weather), environment factors (geology), artificial factors (irrigation and exploitation) to the groundwater dynamic of the district, emphatically analyzed the time complementarity and effects additive of rainfall and irrigation to groundwater dynamic. This paper used the improved gray related analytical method to analyze the relationship between groundwater dynamic and rainfall, irrigation, evaporation and exploitation in recent years (1991~2001), and got the results that irrigation was the main factor affecting the groundwater dynamic.Finally, one of the Artificial Neural Network algorithms--BP algorithm and traditional method GM(1,1) model were used to simulate groundwater dynamic (1991~2002) of 201# well which locates in Zhoucheng Sufang billabong, and the materials of 2003 of this well were used to model checking and prediction. The results showed the precision of BP algorithm was high, reflecting the advantages of ANN model in groundwater dynamic prediction, which had guiding significance to water table monitoring and prediction, reasonable developing and utilizing groundwater in this irrigated district.