Estimation of effective porosity in large-scale groundwater models by combining particle tracking, auto-calibration and <sup>14</sup>C dating
<p>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...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-09-01
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| Series: | Hydrology and Earth System Sciences |
| Online Access: | https://www.hydrol-earth-syst-sci.net/22/4843/2018/hess-22-4843-2018.pdf |
| Summary: | <p>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<sup>2</sup>
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 <sup>14</sup>C 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.</p> |
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| ISSN: | 1027-5606 1607-7938 |