INFLUENCE OF VERTICAL FLOW ON GROUNDWATER TRANSPORT

Two-dimensional analysis of ground-water flow using graphical flow net analysis or numerical modeling is applied to many field settings. However, the assumption of hydrostatic head conditions, implicit in two-dimensional depth-averaged planimetric analyses, is not correct for situations where there is vertical flow such as near a partially penetrating stream. Vertical flow is particularly important when predicting flow paths for contaminant transport. An analytical solution is presented, which calculates the flow paths in the vicinity of a partially penetrating stream. The derivation assumes radial flow towards the stream in the vicinity of the stream, and predominantly horizontal Dupuit flow in the remainder of the region. The analytical solution may be used as a correction to apply to flow paths generated by two-dimensional analysis, or as a screening tool to determine the error when vertical flow is neglected by two-dimensional analysis. To verify the analytical solution, it is compared to numerical simulations of three-dimensional flow in an idealized aquifer for a number of cases with varying degrees of hydraulic conductivity anisotropy. An example illustrates the use of the analytical solution. For the example presented, two-dimensional analysis can underestimate the distance which a contaminant travels before discharging into the stream by almost a mile.