Seepage Face Studies

Seepage faces occur commonly in unconfined groundwater flows. Accurate estimation of the seepage face height is important in both steady-state and transient problems. Earlier modeling studies of water flow dynamics neglected the unsaturated zone but accounted for its contribution to the saturated zone (i.e., zone below the water table) using the specific yield concept. More recent studies use the more realistic variably-saturated representation of water flow, which is based on Richard's equation. Such a representation removes the artificial treatment of the water table as a sharp interface between the saturated zone and the unsaturated zone; the water table is merely the locus of points where the gauge pressure of the water is zero. Variably-saturated numerical models have since been used to investigate seepage problems under steady state and transient regimes.

(Schematic of a seepage face in a beach)

A novel dimensionless formulation for water flow in two-dimensional variably saturated media is presented. It shows that scaling physical systems requires conservation of the ratio between capillary forces and gravity forces. A direct result of this finding is that for two physical systems to be hydraulically similar, the soil in the smaller system has to be coarser than the soil in the larger system. The formulation was implemented in the numerical model MARUN (for MARine UNsaturated), a two-dimensional finite-element model for viscosity-and-density-dependent flows in variably-saturated anisotropic media.

Steady state results from the MARUN model for a coarse-textured domain (alpha=10) and for a fine-textured (alpha=0.5) domain. The figures show the water table, relative soil moisture, and velocity vectors.