应用随机模拟方法确定复杂裂隙含水层中泉点的捕集区域

Using Stochastic Inverse Modeling Method to Obtain Probabilistic Capture Zones of a Spring in a Complex Fracture Aquifer

出于精度考量,研究场地尺度水文地质特征时,采用随机模拟技术建立多个满足场地有限地质信息的情景模型,可以较为有效地表征含(隔)水层结构,并描述目标泉点的捕集区域.但通常受条件限制,场地中的实际钻孔数量可能难以满足随机建模的数据密度要求.基于地面地质分析和一定量的实际钻孔资料,同时借助详实的瞬变电磁物探数据,在物探测点处构建虚拟钻孔,进而建立若干关于地层结构的随机模型(情景模型);采用PEST参数自动识别程序筛选符合水位观测值的情景模型,并复核这些模型的地层结构,以保证情景模型的合理性.基于74个钻孔数据点(包含虚拟钻孔)的转移概率马尔科夫链(TPORGS)共生成503个情景模型,以场地范围内9个地下水位观测点的数据为基准,通过PEST最终筛选出67个可以描述场地水文地质特征的模型,最后由筛选出的模型统计得到目标泉点的概率捕集区域.该建模流程可以在钻孔数据缺乏时,完成场地尺度的随机建模,并获得有效的场地水文地质信息.

Generating a series of stochastic models(realizations)by applying stochastic inverse modeling method is sometimes an efficient way to improve hydrogeological cognition accuracy of a site,such as obtaining a more clarity aquifer structure or a probabilistic capture zone of a spring.However,the borehole data size often cannot meet the requirements of stochastic modeling in a general project.Considering geological analysis result and borehole data,it may be a rational and effective method to translate geophysical prospecting(TEM)points into virtual boreholes to solve the data shortage problem.Using the PEST program,stochastic models established through practical boreholes and virtual boreholes can be screened with groundwater level data as the reference.The stratigraphic structure of the filtered models is then checked artificially to guarantee model geological rationality.In this paper,a total of 503 realizations are generated by using a transition probability Markov chain(T-PORGS)based on 74 data points(including virtual boreholes).With data from 9 groundwater observation points within the site as a benchmark,67 models that effectively describe the hydrogeological characteristics of the site are selected through PEST.Finally,the probabilistic capture zones of the target spring in a fracture aquifer are calculated from these selected models.This modeling process enables stochastic modeling at a site scale even in the absence of sufficient borehole data,providing valuable hydrogeological information for the site.