Determination of Scale-Appropriate Hydraulic Parameters for Simulations of Exchange Between Groundwater and Surface Water

Abstract:

Monitoring wells installed near surface water commonly are used to provide hydraulic gradients and estimates of horizontal hydraulic conductivity (K_h) for simulating exchange between groundwater and surface water. Measurement scale depends on the distances that monitoring wells are situated from the surface-water bodies of interest, commonly ranging from several to hundreds of meters. Determining K_h with a single-well slug test implies that hydrogeologic properties at the well are representative of the porous media between the well and the surface-water body; usually a poor assumption. Measurements of hydraulic gradient and hydraulic conductivity in the vertical direction (K_v) also can be accomplished with shallow piezometers installed in the bed of a stream or lake or wetland. The scale of these measurements is generally on the order of centimeters to a meter or two. Estimates of anisotropy can be obtained when data from in-water piezometers are combined with data from near-shore monitoring wells although, once again, K_v determined at the screened interval of the piezometer may not adequately represent the interval between the screen and the sediment-water interface. However, combining measurements of flow across the sediment-water interface with hydraulic gradients determined from in-water piezometers and near-shore monitoring wells provides the ability to calculate spatially integrated values for both K_h and K_v. These values are scaled based on the locations of the wells and are usually more appropriate as calibration parameters for groundwater-flow models that simulate groundwater-surface-water exchange.