Using MODFLOW code to approach transient hydraulic head with a sharp‐interface solution |
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| Authors: | Carlos Llopis‐Albert David Pulido‐Velazquez |
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| Affiliation: | 1. Instituto Geológico y Minero de Espa?a (IGME), Valencia, Spain;2. Instituto Geológico y Minero de Espa?a (IGME), Granada, Spain;3. Departamento de Ciencias Politécnicas, Escuela Universitaria Politécnica, UCAM Universidad Católica San Antonio de Murcia, Murcia, Spain |
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| Abstract: | Saltwater intrusion problems have been usually tackled through analytical models because of its simplicity, easy implementation and low computational cost. Most of these models are based on the sharp‐interface approximation and the Ghyben–Herzberg relation, which neglects mixing of fresh water and seawater and implicitly assumes that salt water remains static. This paper provides insight into the validity of a sharp‐interface approximation defined from a steady state solution when applied to transient seawater intrusion problems. The validation tests have been performed on a 3D unconfined synthetic aquifer, which include spatial and temporal distribution of recharge and pumping wells. Using a change of variable, the governing equation of the steady state sharp‐interface problem can be written with the same structure of the steady confined groundwater flow equation as a function of a single potential variable (?). We propose to approach also the transient problem solving a single potential equation (using also the ? variable) with the same structure of the confined groundwater flow equation. It will allow solving the problem by using the classical MODFLOW code. We have used the parameter estimation model PEST to calibrate the parameters of the transient sharp‐interface equation. We show how after the calibration process, the sharp‐interface approach may provide accurate enough results when applied to transient problems and improve the steady state results, thus avoiding the need of implementing a density‐dependent model and reducing the computational cost. This has been proved by comparing results with those obtained using the finite difference numerical code SEAWAT for solving the coupled partial differential equations of flow and density‐dependent transport. The comparison was performed in terms of piezometric heads, seawater penetration, transition zone width and critical pumping rates. Copyright © 2014 John Wiley & Sons, Ltd. |
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| Keywords: | seawater intrusion analytical solutions sharp interface coastal aquifers critical pumping rates Ghyben– Herzberg calibration |
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