Evolution And Conservation Of Groundwater In Hebei Plain To The South Of Beijing And Tianjin

Hebei Plain to the south of Beijing and Tianjin is considered as the region where the water resource problems are the worst in Huabei area, as well as the main area which is going to accept the water from south-to-north water transferring project. In the past 50 years, because of many events such as surface water retention projects, channel regulation works, artificial exploitation of shallow groundwater and deep groundwater and the decrease of precipitation etc, there gradually emerge many water resource environment problems: drop of regional water level, occurrence of depression cones, depletion of channels and lowlands, shrinking of swamps, seawater intrusion, land subsidence, serious water shortage and so on. In this paper, by studying the evolution characteristics and mechanism of groundwater, as well as by identifying the dominated factor and the extent of its influence on groundwater evolution, ways and measures of restoring and conserving the regional groundwater after the practice of the middle route of the South-to-north water transferring project are carefully discussed.Groundwater extraction of study area assumes 90 percent or so of total water supply, and this has been providing guarantee for increase of regional population and food supplies. Among shallow groundwater exploitation and deep groundwater mining, the agricultural extraction occupies 83.35 percent and 66.1 percent respectively. As a result, groundwater overdraft reaches 25.4×10~8m~3/a and the accumulated consumption of shallow storage resource arrives at 380.6×10~8m~3. At present, the regional depression cones are embedded and multiplied each other, consequently groundwater flow direction transforms from natural situation flowing from west to east to another condition that water flows from surroundings of each depression cone to its center. Meanwhile, the artificial mining makes up the main part of groundwater discharge.Precipitation of study area presents a decreasing trend on the whole, in 1980s and 1990s the average precipitation decreased by 73.1mm and 61.3mm respectively, and the groundwater resource reduced by 23.8 percent. Now the current groundwater extraction is about 105.45×10~8m~3, and the available resource reaches 80.08×10~8m~3/a. Moreover, the correlation degree between groundwater mining and groundwater drawdown and that between precipitation and groundwater drawdown is 0.711 and 0.601 separately. Conclusion from the analysis indicates that falling of groundwater level results from human activities, groundwater exploitation is the major influence factor and surface runoff retention from the mountain outlet takes the second place.The reservoir area of the plain, ahead of TaiHang Mountain, occupies 81.8 percent of the total reservoir areas, and its reservoir capacity reaches 192×10~8m~3 under the current water level condition. So it is feasible to make groundwater conservation aimed at recovery and utilization of groundwater. Under the control of the following three rules, which are groundwater utilization restriction, subsurface reservoir capacity and optimization use of multi-source water, patterns of groundwater conservation can be classified into three kinds: decrease of groundwater mining, use of storm flood and retention of foreign water from south-to-north water transferring project. Among these patterns, the first one belongs to indirect reservoir, instead the last two ones belongs to direct reservoir.