| Groundwater is an important part of water resources. In most areas of our country, the present situation of groundwater is not optimistic. Changwu Tableland is the area in shortage of groundwater resources, where the contradiction between water supplies and demands is serious year by year due to the long-term blind and excess exploitation leading to continuous groundwater lowering. Therefore, it is important to study the variation of groundwater and predicate the change tendency for water resource utilization.This study is based on the detailed analyses of relevant data and the results of previous studies and combined with the analysis of the precipitation data during 1957-2008 in order to understand the shortage of groundwater resources on Changwu Tableland. A preliminary understanding of the changing situation of groundwater and the influence factors has been reached. The situation of rainfall in the area and the effects of rainfall on groundwater level change are systematically analyzed. The time-series analysis theory is applied to analyze and forecast the dynamic variation of groundwater on Changwu Tableland. First, the trend component of groundwater level dynamic variation is picked up by polynomial calibration, the periodic component is extracted by spectrum analysis, and the stochastic component is simulated by using autoregression (AR) model. Then, a forecasting model is established through superposition of the three components. According to the monthly averaged groundwater level data of the five wells on Changwu Tableland, the dynamic simulating model and forecasting model of groundwater level are established by using SAS, respectively, and the accuracy of models are analyzed. The main research contents and conclusions of this thesis are as follows:(1) The analysis of the rainfall data from the Changwu Weather Bureau indicates that the distribution of monthly rainfall in the area is not uniform. The continued dry season is longer than the continued wet season. The total annual precipitation varies greatly from year to year.(2) According to the data from the monitoring well No. 552 with complete data preservation, the groundwater level depth drops from 25.30 to 31.84 m, a total decline of 6.54 m during the 32 years, with a slow decrease from 1976 to 2008 and a significant decrease from 1996 to 2008. In the recent years, the decline amplitude of groundwater level has become larger and larger. The prediction for the years after 2008 indicates that a continuing decline of groundwater level exists in some districts of the area. The decline must be controlled in time.(3) Based on the Time-Series method, the data observed from the five representative wells on Changwu Tableland are mainly analyzed and the Time-Series model is established. The analysis of the model shows that the variation of groundwater level in the area presents two major periods. One is the 1 year period, which may reflect the seasonal variation of groundwater level. Another is the 7.4 to 10 years period, which has the same trend as the period of rainfall and becomes longer and longer.(4) The accuracy of the prediction model is higher. The model can better simulate the variation of groundwater level in the area. Moreover, the model can forecast the prospective situation of groundwater level under the premise that the restrictive factors does not change. The prediction error can magnify with the change of the outside factors. Therefore, basic data should be updated in time and a prediction model should be established with new data in order to improve the accuracy.
|
PDF Full Text Request