A Study Of The Characteristics And Regulation-Storage Capacity Of The Zhangfang Karst-groundwater Reservoir In Beijing

Beijing is in the north of Huabei Plain, is the big city in the world which usesgroundwater as the main water supply source. Two thirds of water is groundwater.The precipitation distributes irregularly and alternates abundance and deficiency,which leads to low efficiency of water use and contradiction between supply anddemand. Water shortage restricts the sustainable development of society andeconomy. Using storage capacity of aquifer to set up the groundwater reservoir,which can realize water storage and adjustment and improve the water utilizationefficiency, is the main approach to relax the tension of water resources.The karst-water is the import water resources in Beijing, which has complex systemcharacteristics due to irregular storage media. The paper discussed the characteristics of theZhangfang karst-water system based on water source site selection, engineering investigation andwater production. Considering the dominating factors such as paleoclimate, topography andgeological structure, the author used geophysical and hydrogeological exploration,hydrochemistry and isotope method to analyze regional tectonic stress field, hydrochemical fieldand groundwater dynamic field. Then, the condition of recharge, runoff and discharge wasdiscussed, and the groundwater age was tested by using deuterium and oxygen isotope and CFCstracer. Three water-rich zones were classified named Baidai, Shiwo and Changgou, whichdetermined the range of karst-water reservoir. The reservoir area is about 401 km~2, in which themountain area for recharge is 280 km~2. The result of research shows that the distribution ofkarst-water is dominated by geological structure. The water yield property distributes irregularly.The recharge condition is good and water circulates fast. On the basis above and dynamicmonitoring of groundwater level, the numerical groundwater flow model was established toforecast the drawdown of groundwater table and evaluate the regulation-storage capacity ofgroundwater reservoir. Thereafter, the joint regulation-storage plan of surface water andgroundwater was put forward.The Zhangfang karst groundwater reservoir is in the Piedmont, which isbelongs to the semi-open type karst-water system and has good recharge condition.The average annual groundwater could be product is 2330×10~4m~3/a, and the largestregulation-storage capacity is 4690×10~4m~3/a. The Juma river enters the karst-waterreservoir in northwest with runoff of 11804×10~4m~3/a. The karst-water region hasjoint regulation-storage condition. The Shengtian trench can be used to adjust watersupply of karst-water reservoir which has excellent storage function and remediesthe deficiency of surface water. So, the utilization efficiency of water resourcescould be improved. The research shows that the joint regulation-storage can meetwater supply 1.3-1.5×108m~3/a.