GroMoPo Metadata for Wadden Sea advective transport model

Effective porosity plays an important role in contaminant management. However, the effective porosity is often assumed to be constant in space and hence heterogeneity is either neglected or simplified in transport model calibration. Based on a calibrated highly parametrized flow model, a three-dimensional advective transport model (MODPATH) of a 1300 km(2) coastal area of southern Denmark and northern Germany is presented. A detailed voxel model represents the highly heterogeneous geological composition of the area. Inverse modelling of advective transport is used to estimate the effective porosity of 7 spatially distributed units based on apparent groundwater ages inferred from 11 C-14 measurements in Pleistocene and Miocene aquifers, corrected for the effects of diffusion and geochemical reactions. By calibration of the seven effective porosity units, the match between the observed and simulated ages is improved significantly, resulting in a reduction of ME of 99 % and RMS of 82 % compared to a uniform porosity approach. Groundwater ages range from a few hundred years in the Pleistocene to several thousand years in Miocene aquifers. The advective age distributions derived from particle tracking at each sampling well show unimodal (for younger ages) to multimodal (for older ages) shapes and thus reflect the heterogeneity that particles encounter along their travel path. The estimated effective porosity field, with values ranging between 4.3 % in clay and 45 % in sand formations, is used in a direct simulation of distributed mean groundwater ages. Although the absolute ages are affected by various uncertainties, a unique insight into the complex three-dimensional age distribution pattern and potential advance of young contaminated groundwater in the investigated regional aquifer system is provided, highlighting the importance of estimating effective porosity in groundwater transport modelling and the implications for groundwater quantity and quality assessment and management.

有效孔隙率在污染物管理中扮演着至关重要的角色。然而，有效孔隙率通常被假定为在空间上保持恒定，因此该区域的异质性要么被忽略，要么在传输模型校准过程中被简化处理。基于校准的高参数化流动模型，本文提出了一项针对丹麦南部和德国北部1300平方公里海岸地区的三维对流传输模型（MODPATH）。一个详细的体素模型代表了该区域高度异质的地质组成。通过对流传输的反向建模，根据从更新世和米奥辛含水层中推断出的11个碳-14测量的地下水流年龄（已校正扩散和地球化学反应的影响），对7个空间分布单元的有效孔隙率进行了估算。通过校准这七个有效孔隙率单元，显著提高了观测值与模拟值之间的匹配度，与均匀孔隙率方法相比，模型误差（ME）降低了99%，均方根误差（RMS）降低了82%。地下水流年龄范围从更新世几百年的时间跨度到米奥辛含水层几千年的时间跨度不等。在各个采样井处的粒子追踪得到的对流年龄分布显示，对于较年轻的年龄，呈现出单峰（对于较老的年龄，呈现出多峰）形状，从而反映了粒子在其迁移路径上所遭遇的异质性。估算出的有效孔隙率场，其值介于粘土层的4.3%和沙层形成的45%之间，被用于分布式平均地下水流年龄的直接模拟。尽管绝对年龄受到各种不确定性的影响，但本研究提供了对所研究区域含水层系统中复杂的三维年龄分布模式和年轻污染物地下水潜在推进的独特见解，突出了在地下水传输模型中估算有效孔隙率的重要性及其对地下水数量和质量评估与管理的影响。