GroMoPo Metadata for Mahantango Creek MODFLOW model

Surface refraction seismic surveys were conducted within a 7.3 km(2) east-central Pennsylvania watershed to characterize the geometry of its shallow layered and fractured bedrock, These data were augmented with observations from 29 rock cores, Hydraulic conductivity (K) of the bedrock was determined by interval packer testing within the boreholes. Finally, the MODFLOW ground water model was applied to the layered aquifer geometry in a three-dimensional format to determine watershed-scale aquifer parameters by model calibration to observed watershed data. Seismic testing showed that the aquifer could be characterized by four distinct layers, each with its own characteristic seismic velocity Hydraulic conductivity determined by field testing decreased with depth, ranging from greater than 1.0 m day(-1) in the shallow, highly fractured layer to approximately 0.01 m day(-1) in the regional aquifer, Its distribution with depth reflected the increase in seismic velocities and decrease in extent of fracturing observed in the cores. Aquifer geometry determined from seismic testing and rock cores was used to define model layer geometry, and K values from model calibration compared favorably to those determined by field testing. The ground water model was also used in calibration mode to determine specific yields (S-y) of the characteristic fracture layers, These were all low, ranging from 0.005 in the highly fractured layer to 0.0001 in the regional aquifer. When aquifer geometry determined from detailed seismic surveys is used as the basis for watershed-scale ground water modeling in these shallow layered and fractured systems, hydraulic parameters derived by field testing compare well to those determined by model calibration.本研究于宾夕法尼亚州中东部一处面积7.3平方千米的流域内开展了地表折射地震勘探，以刻画其浅层层状裂隙基岩的几何形态。本次研究辅以29组岩芯观测数据对勘探结果进行补充。通过钻孔内的间隔封隔器测试，测定了基岩的导水系数（Hydraulic conductivity, K）。最后，将三维格式的层状含水层几何结构导入MODFLOW地下水模型，通过匹配流域观测数据开展模型校准，以此推求流域尺度的含水层参数。地震勘探结果表明，该含水层可划分为4个特征迥异的层位，各层均具有独特的地震波速。野外实测得到的导水系数随深度增加而降低：浅层高裂隙层的导水系数大于1.0米/天，而区域含水层的导水系数约为0.01米/天。导水系数随深度的分布规律，与岩芯观测到的地震波速升高、裂隙发育程度降低的趋势一致。基于地震勘探与岩芯分析得到的含水层几何结构，用于确定模型的层位设置，且模型校准得到的导水系数与野外实测结果吻合良好。本次地下水模型还通过校准模式，推求了各特征裂隙层的给水度（specific yields, S_y），其数值普遍偏低：高裂隙层的给水度为0.005，区域含水层的给水度则为0.0001。当以精细地震勘探得到的含水层几何结构作为这类浅层层状裂隙流域地下水模型的构建基础时，野外实测得到的水力参数与模型校准得到的参数具有良好的一致性。