北京西山奥陶系岩溶水数值模拟及地下水开采环境效应分析

【作者】 朱锋；

【导师】 宫辉力；

【作者基本信息】 首都师范大学 ， 地图学与地理信息系统， 2014， 博士

【摘要】 北京西山奥陶系岩溶水分布在北京西山山区及山前地带,属于大清河水系大石河流域和永定河水系,水质优良,开发潜力高,是北京市的重要后备水源之一。为了合理开发利用该区地下水资源,缓解由于地下水开采所引发的地质环境问题,本文通过收集整理该区气象水文数据、基础地质数据、水文地质数据等相关资料,以水文地质学、地下水动力学理论为基础,在GIS技术支持下,综合分析地下水水位数据、水文地质钻孔及剖面、抽水试验结果、水化学及同位素结果,系统研究了西山奥陶系岩溶水的补径排特征,进一步探明了该区水文地质条件；在此基础上,结合RS技术与GIS空间分析方法及可视化技术确定了该区水文地质参数的分区及取值,并采用数值模拟技术构建了以奥陶系岩溶水为主体的概念模型和数值模型,通过评价西山奥陶系岩溶水补给资源量及可采资源量,确定了该区地下水的最佳开采方案,研究结果可以为西山地区奥陶系岩溶水资源的合理开发利用提供科学依据。在模型的构建及运用过程中,主要针对以下内容进行了研究并取得了相关结论：1、构造对奥陶系岩溶水径流模式的影响研究区褶皱断裂众多,对奥陶系岩溶水的补径排条件起着重要的控制作用,本次研究通过分析收集的相关资料,采用地下水水位曲线法、地下水水化学方法及数值模拟方法,着重分析了香峪向斜及永定河断裂对奥陶系岩溶水径流模式的影响,提出了西山奥陶系岩溶水径流模式的新认识：香峪向斜具有明显的阻水作用,军庄地区奥陶系岩溶水不能以深循环的形式通过该向斜,永定河断裂则是重要的导水通道,军庄地区奥陶系岩溶水接受补给后,约有75%的水量会沿着该断裂向八宝山断裂进行径流,并最终向玉泉山地区进行排泄,其余25%的水量则沿着香峪向斜北翼向温泉地区径流。2、奥陶系岩溶水资源评价研究区已有奥陶系岩溶水资源评价主要围绕水源地建设进行,较少考虑奥陶系岩溶水的系统性。本文利用数值模型,从地下水补给资源量及可采资源量两个角度对北京西山奥陶系岩溶水资源进行了首次系统评价。结果表明：2000年-2012年,奥陶系岩溶水系统年均补给量约为11777×104m3/a,其中永定河河道渗漏补给和大气降水入渗补给是主要补给源：永定河河道年均渗漏补给量约为9027×104m3/a,约占总补给量的76%；年均大气降水补给量约为2472×104m3/a,占总补给量的21%。其他补给源还包括边界侧向流入、大石河侧向补给以及其他含水层的越流补给,但补给量少,仅占总补给量的3%左右。北京西山奥陶系岩溶水年均可采资源量约为8422×104m3/a,最大可采资源量约为11699×104m3,最小可采资源量仅为3657×104m3。目前奥陶系岩溶水已经超采,其年均超采量约为2868×104m3/a。3、地下水最佳开采方案本次研究以北京市供水规划为基础,依据不同目标设计了现状开采方案、理想开采方案(按年均可采资源量开采)以及逐年压采方案,并对不同方案进行了模拟预测。结果表明：2013年-2030年预测期内,现状开采条件下,北京西山地下水开采量达34962×104m3/a,但水位下降速度快,地下水超采比较严重,其中第四系地下水超采4465×104m3/a,奥陶系岩溶水超采量约为442×104m3/a；理想开采方案和压采方案条件下,地下水水位都有所回升,地下水系统处于正均衡状态；从开采量来看,理想开采方案开采量约为27988×104m3/a,分期压采方案开采量约为28521×104m3/a。对比地下水开采量、地下水水位变化以及地下水水均衡状况可知,分期压采是研究区地下水最佳开采方案。4、地下水开采环境效应分析研究区已有地质环境问题主要包括：沙河地区地面沉降、玉泉山地区奥陶系岩溶水水质污染以及洼里地区岩溶塌陷风险,而已有研究主要考虑该区供水安全,对地下水开采导致的地质环境问题关注相对较少。本次研究利用数值模型对不同开采方案进行了模拟,并对诱发的地质环境问题进行了分析,结果表明：按方案一现状开采量进行开采,2013年-2030年,沙河地区第四系承压水水位不断下降,其年均下降速率最小值约为1.7m/a,超过水位下降速率临界值1m/a,地面沉降发生风险大；玉泉山地区奥陶系岩溶水和第四系地下水水位下降速率均约为1.2m/a,奥陶系岩溶水补给第四系地下水水量为144×104m3/a,第四系地下水补给奥陶系岩溶水水量约为64×104m3/a,奥陶系岩溶水水质污染风险较大；洼里地区水位下降速度约为0.87m/a,预测末期,洼里砾岩地下水水位低于洼里砾岩顶板标高,岩溶塌陷风险大。方案二按年均可采资源量进行开采,沙河地区第四系承压水水位下降趋势得到了遏制,预测末期水位和预测初期水位基本一致,地面沉降风险较小；玉泉山地区奥陶系岩溶水和第四系地下水水位回升速度分别为0.08m/a和0.02m/a,不存在第四系地下水补给奥陶系岩溶水现象,奥陶系岩溶水越流补给第四系地下水水量约为925×10-4m3/a；洼里砾岩地下水预测末期水位达10.6m,高于洼里砾岩顶板标高,预测期内岩溶塌陷风险小。方案三按分期压采方案进行开采,沙河地区第四系承压水水位回升速度达到了0.3m/a,地面沉降发生风险降低；玉泉山地区奥陶系岩溶水水位和第四系水位不断回升,其中奥陶系岩溶水补给第四系地下水水量达到了1450×104m3/a,奥陶系岩溶水水质污染风险小；洼里砾岩地下水预测末期水位9.7m,高于洼里砾岩顶板标高,,发生岩溶塌陷的风险较小。更多还原

【Abstract】 Beijing Xishan Ordovician karst water is one of the most importment back-up water sources in Beijing. The karst water distributes in Beijing Xishan Mountain and piedmont area, and be-longs to Dashi River basin of Daqing River system and Yongdinghe River system. The water quality is excellent and the mining potential is high. To exploit the water source scientigically and legitimately and ease the geological environment problems caused by the groundwater over-exploitation, some meteorological and hydrological data, basic geological data, hydro-geological data and other related data are collected and managed by the GIS software. Based on the Hydrogeology, groundwater dynamics theory, combined with the analysis of groundwater level data, hydrogeological drilling and profilem, pumping test results, water chemistry and iso-topic results, the system features of the Karst water’s supply, run-off and excretion are re-searched and makes the hydrogeological condition more distinct. On the basis, the conceptual model and numerical model of Ordovician karst water as main are builted with RS, GIS and nu-merical simulation. With the model, the resources of the Ordovician karst water is evaluated, and the best exploitation plan is determined. The results can prove scientific basis for grounderwater exploitation. In the process of building model, some conclusions are acquired as follows:1.The runoff pattern analysis of Ordovician karst water affected by the geological structureNumerous folds and faults distribute in the study area and control the boundary of Ordovi-cian karst water. By analysing the related data, with the groundwater level curve, groundwater chemistry methods and numerical simulation, the affection of the Xiangyu syncline and the Yongding River fracture to the run-off patterns of Ordovician karst water is paid close atten-tion.The results show that: the karst water can not go through the syncline and the Yongding River fracture is an important water channel. About75%of the water will go along the fault to Babaoshan fracture, and the other25%of the water will run along the north owing of the syn-cline to Wenquan area.2. Resources assessment of Ordovician karst waterThe resources evaluation results of Ordovician karst water using the numerical model show that:from2000to2012, the average annual recharge is about11777×104m3/a, which Yongding riverleakage recharge accounts for about76%, the average annual of precipitation supply is about2472×104m3/a; the annual recoverable resources of about8422×104m3/a, the most recov-erable resources is about11699x104m3/a and the least recoverable resources is only about36572×104m3/a. Recently, the karst water has been exploited redundantly and the average annual water balance is about-2868×104m3/a. 3. The research of optimum exploitationAccording to the different status of the target,3programs are designed including status quo exploitation, ideal exploitation (according to the average annual amount of recoverable resource and reducing exploitation yearly. All the programs are simulated using the numerical models.The results show that:from2013to2030, in program1, about34962×l04m3water will be exploited every year, but the water level drops quickly, the water balance of Ordovician karst water is about-4465×104m3/a and that of Quaternary groundwater is about-442×104m3/a; the ground-water level in program2and program3is rising and both water balance is positive,which indi-cates that program2and program3will not cause a large drawdown. Consider the quantity of exploitation, the gorounderwater level and the balance of the groundwater sysytem, the amount of water supplied in program3is the most (28521×104m3/a), and program2is about27988×104m3/a, so program3can be used as the best mining plan.4. Analysis of Environmental impaction caused by groundwater exploitationThe geological environment problems in study area include land subsidence in Shahe, Or-dovician Karst Water pollution in Yuquan Mountain and karst collapse risk in Wali. The differ-ent simulation results show that:As status puo mining plan,the confined water level of Quaternary is falling in Shahe area and the annual rate is about1.7m/a, exceeds the critical rate of decline(lm/a) and will induce land subsidence disaster; Ordovician karst water and Quaternary water level decline in Yuquan Mountain area, the annual rate is about1.2m/a, the Ordovician karst water and Quaternary groundwater can recharge each other, which will lead to the pollution of Ordovician karst wa-ter.The recharge water is about144x104m3/a from Ordovician karst water to Quaternary groundwater, and about64×10m/a from Quaternary groundwater to Ordovician karst water; The groundwater level drops fastest (0.87m/a), the groundwater level below the Wali conglom-erate gravel rock roof elevation, karst collapse risk will be high.According to program2, the confined water level decline has been effectively curbed in Shahe area, and the water level rise slowly; Under the program, Ordovician karst water and Quaternary groundwater level in Yuquan Mountain is recovering, the recovery rate was0.08m/a and0.02m/a respectively. There is no water from Quaternary groundwater to Ordovician karst water, and about925×10m3/a from the Ordovician karst water to Quaternary groundwater;The final level of the groundwater in Wali area is high up to10.6m, higher than Wali conglomerate roof elevation, which means the karst collapse risk is low.Under program3,the confined water level rises rapidly, reaching0.3m/a, which indicates that the risk of the occurrence of ground subsidence is smaller;the Ordovician karst water level and the Quaternary groundwater level continue to recover in YuQuan mountain, the water from Ordovician karst groundwater to Quaternary water reached1450×104m3/a, Ordovician Karst Water pollution risk will reduce; the final water level is about9.7m in Wali area, and the karst collapse risk is also very small.更多还原