| Groundwater in Beijing has long played an important role in urban water supply. Especiallyin the late of1970s, groundwater accounted for about two-thirds of the total water supply,guaranteeing residential demand and development of industry and agriculture. The naturalwater resources per capita consumption in Beijing is less than300m~3, facing the problem oflacking water. After1990, Beijing’s rapid development in economy and society, with theincreasing size of city, overexploitation of groundwater, results in serious deficit ofgroundwater resources and deterioration of groundwater environment, demonstrating crisis ofwater resources. Shortage of water resources has become the greatest bottleneck in thedevelopment of Beijing and stability of society. In2010, Beijing proposed the development goalof constructing International City with Chinese characteristics, demanding a substantialincrease in water resource guarantee capacity. In order to alleviate water crisis in Beijing,Tianjin and North China, the Party Central Committee and State Council decided to build theNorth Water Transfer Project.When the project come into operation, water supply in Beijing willbe composed by water from the North Water Transfer Project, local surface water, localgroundwater and renewable water. In order to guarantee water supply security of the capitaland make the best use of multiple water resources, the water from the North Water TransferProject, local surface water, local groundwater and renewable water is going to be dispatcheduniformly and supplied together, using water resources scientifically and reasonably andexploiting comprehensive benefit of water resources.Groundwater storage and regulation is going to be a critical component for water resourcesreasonable distribution and scientific dispatch when water from the North Water TransferProject arrives Beijing. Building groundwater reservoir using underground space is a methodto adjust water space-time distribution artificially, storing water from the North Water TransferProject and surplus water from reservoir in flooding year, and extracting in the dry year andfacing incidence, which is helpful in using water from the North Water Transfer Projecteffectively and completely, improving response to water crisis and water supply guaranteedegree. The western suburb groundwater reservoir is located in the Yongdinghe alluvial andpluvial fan. The site has good water storage capacity due to thick sand gravel layers, naturalwater resistant boundaries, permeable river course and sand gravel pits, and the1,2,3,4and7well fields. It is also a proper site for water storage and regulation for its location close to theNorth Water Transfer Project instrument. The site could be used to build a groundwaterreservoir to store surplus water from the North Water Transfer Project, raising groundwaterlevel in the middle-up stream of the Yongdinghe alluvial and pluvial fan, and exploitinggroundwater in the3rd well field near the groundwater reservoir to meet demand of the cityduring dry years.The recharge mode, recharge capacity and recharge projection method are analsizedbased on collected material, field investigation, groundwater numerical simulation andcomprehensive study in Beijing during the past years.Conclusions following could be drawn:The single and thick layer with coarse grains in the middle-up stream of the Yongdinghealluvial and pluvial fan is the main well fields for Beijing. The multiple sand layers in thedownstream in the Yongdinghe alluvial and pluvial fan is the natural water resistant boundary.Therefore, the aquifer in the middle-up stream of the Yongdinghe alluvial and pluvial fan couldbe used to build groundwater reservoir.The groundwater level in June of1983, which was close to the environment andengineering warning line compared with groundwater level between1960s and1980s, couldbe set as recovery groundwater level of Beijing Plain. The storage volume of groundwaterreservoir was calculated to be9.6×108m3based on groundwater level in2010and recoverygroundwater level.Seven pits in Nanhanhe river course, the Jingyuan railway bridge over Yongdinghe riverand Lugou bridge flood diversion sluice river course, Daotian and Machang flood detentionreservoir, Huangcun, Laoshan and Qiaohuying and180large diameter wells in Nanhanhe,green land along the sides of Yongdinghe inlet channel to reject. The total recharge capacity ofthe western groundwater reservoir was calculated to be41.19m3/s based on the comparisonof historical and current recharge experiment results. The water source will be composed by the surplus water from the North Water TransferProject, surplus water from local reservoir and flood from the gorges between Guantingreservoir and Sanjiadian reservoir and flood from the Yongdinghe. The flow rate could beadjusted artificially when surplus water from the North Water Transfer Project, surplus waterfrom local reservoir and flood from the gorges between Guanting reservoir and Sanjiadianreservoir will be used, but flood from the Yongdinghe could not be controlled, which means apassively recharge. Controllable water source (mode I) and great flood (mode II) could beclassified due to source and characteristics of recharge water.The total recharge capacity of the project could calculated to be6.20m3/s and12.73m3/swhen large diameter wells will have been built in Nanhanhe and inlet channel of Yongdingheunder the mode I. The total recharge capacity of the project could calculated to be14.70m3/sand7.56m~3/s when groundwater reservoir will have been built in Yongdinghe and flooddetention reservoir under the mode II.Seven recharge modes, including current mode, increasing large diameter wells andprojection-union, were proposed, the total recharge capacity of the recharge projection wascalculated to be2.93×108m~3. Groundwater level will rise32m, the influence area will be340km2, and the influence area will be widen gradually. The average storage rate in thegroundwater reservoir could be52.87%after5years’ recharge and the average storage ratecould be71.86%in the simulation region. The recharge water could create great benefit in thefuture.Total hardness, TDS and nitrate of groundwater in City suburb can decrease when upperand middle section of Yongdinghe alluvial and pluvial fan is recharged by high quality waterfrom the North Water Transfer Project and surplus water from reservoir in flooding, and thewater quality beyond standard is improved subsequently, which has significance onguaranteeing water supply of the third, fourth and the seventh water plants. |
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