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

Friday, 19 December 2014: 9:45 AM
Donald O Rosenberry, USGS Central Region Office, Lakewood, CO, United States; US Geological Survey, Lakewood, CO, United States
Monitoring wells installed near surface water commonly are used to provide hydraulic gradients and estimates of horizontal hydraulic conductivity (Kh) 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 Kh 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 (Kv) 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, Kv 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 Kh and Kv. 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.