基于数值模拟的岩溶地下水源保护区划分技术研究

Research on the division technology of karst groundwater source protection areas based on numerical simulation

以山东省邹城市某岩溶水源地为例,研究数值模拟方法在岩溶地下水水源地保护区划分中的应用,以及水文地质参数对于水源地保护区划分结果的影响。基于GMS软件构建了研究区三维非稳定流地下水数值模型,采用质点追踪技术,通过反向追踪示踪粒子在运移100 d、1 000 d以及25 a后的位置及迁移轨迹,对该岩溶水源地进行保护区划分;改变数值模型中的主要水文地质参数,以变化后的保护区面积作为衡量参数敏感度的指标,并计算各参数的敏感度系数,研究水文地质参数对于保护区划分范围的影响。结果表明:当参数改变幅度在20%范围内时,一层垂向渗透系数(VK_1)的敏感度系数最大可达到2.63×10^(-3),二层垂向渗透系数(VK_2)的敏感度系数最大可达到3.64×10^(-3);垂向渗透系数的敏感度明显高于其他参数,说明垂向渗透系数对保护区划分范围的影响最大。因此,在应用数值模拟法对岩溶地下水源地进行保护区划分时,应尤其注意模型中各含水层垂向渗透系数取值的准确性和合理性。

Zoucheng City is located in the southwest of Shandong Province with a total area of 1,616 km 2.Taking a karst water source in Zoucheng City as an example,the application of numerical simulation methods in the division of karst groundwater protection zoning and the effect of hydrogeological parameters on the classification results of water source protection zones were studied.The water source is located in the middle of the Guoliji monoclinic karst water system,with Wangyun river in the south.Groundwater is abstracted from the fractured karst aquifer comprising the Middle and the Lower Ordovician carbonate rocks,with the single well yield of more than 3,000 m 3·d-1.There are two abstraction well fields in the water source,of which the first well field consists of 6 production wells and 4 production wells in second one.The karst groundwater runs from the southwest to the northeast,and mainly receives the leakage recharge of the overlying porous aquifer and the lateral runoff recharge.Using GMS software,a three-dimensional unsteady groundwater numerical model was constructed.Using particle tracing technique,the protection area of the karst water source area were divided by tracing the position and the migration trajectory of tracer particles after 100 days,1,000 days and 25 years.Taking the change of the protection area after changing the parameters as the index to measure the sensitivity of the parameters,the sensitivity coefficient of each parameter was calculated and the influence of the hydrogeological parameters on the division scope of the protection area was studied.The numerical simulation shows that the maximum migration distance of the tracer particles after 100 d is 44.91 m,the maximum migration distance after 1,000 d is 301.85 m,and the maximum migration distance after 25 a is 1,523.27 m.According to this result,the area of the primary protection zone is 1.27×10 4m 2,the area of the secondary protection zone is 0.42 km 2,and the area of the quasi-protection zone is 3.47 km 2.The sensitivity analysis result shows that when the parameter change range is within 20%,the sensitivity coefficient of vertical permeability coefficient VK 1 of the first layer can reach 2.63×10-3,and the sensitivity coefficient of vertical permeability coefficient VK 2 of the second floor can reach 3.64×10-3.The sensitivity of the vertical permeability coefficient is significantly higher than other parameters,indicating that the vertical permeability coefficient has the greatest impact on the division of the protection area.Therefore,when applying the numerical simulation method to divide the protection areas of karst groundwater sources,we should pay special attention to the accuracy and rationality of the vertical permeability coefficient of each aquifer in the model.