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A sub‐grid representation of groundwater discharge using a one‐dimensional groundwater model

Simple models of groundwater flow have limited capability of representing spatial waterlogging/salinization due to the mismatch in scale between model cell size/process conceptualization and actual process scale. This paper presents a method for utilizing increasingly available high‐resolution digital elevation data to develop a sub‐grid parameterization for groundwater discharge and surface waterlogging. This enables simple groundwater models to represent the actual area of waterlogging/salinization better. The approach utilizes a ‘zero‐piezometric surface’ (i.e. a planar surface that passes through the lowest point of each element in a groundwater model). The difference in elevation between the zero‐piezometric surface and a high‐resolution digital elevation model (DEM) provides a distribution of depth to the zero‐piezometric surface (at the DEM scale) for each element in the model. Traditional methods for evaluating surface discharge can then be applied at the DEM cell scale to the distribution of depth to zero‐piezometric surface to derive a relationship between depth to piezometric surface and net recharge/discharge, for each element in the model. A simple one dimensional groundwater flow model, FLOWTUBE, is used to demonstrate the approach. Copyright © 2003 John Wiley & Sons, Ltd.