394366 - One-Dimensional Analytical Solutions for Vertical Seepage of Perched Water Under Transient Condition
Wednesday, June 6
10:30 AM - 12:00 PM
Location: Lakeshore B
Mike Riley, Olympia, Washington – Anchor QEA, LLC
A perched zone is formed in the vadose zone when the vertical flow of water that infiltrates from the ground surface is restricted by a low-permeability layer. Although the flow of perched water is three dimensional, one-dimensional analytical solutions for vertical seepage through a restricting layer are applicable to large areas where three-dimensional effects at the edge of the perched area are relatively minor compared to vertical seepage.
An existing one-dimensional analytical solution (e.g., Bouwer 1999) solves for the height of perched water under steady state when the infiltration rate is constant. In this presentation, a number of transient solutions are presented for when the infiltration rate is variable, including how long it takes a perched water mound to dissipate when infiltration becomes zero (e.g., by an ideal cap); how fast the perched water mound declines if infiltration is reduced (e.g., by a non-ideal cap); and how the perched water mound changes if infiltration is reduced to zero first and then increases to an asymptotic level (e.g., as a cap deteriorates over time).
When empirical data are available for the change of perched water mound over time, these analytical solutions can be used to estimate hydraulic parameters and predict perched water mound and seepage rate through a restricting layer under various capping scenarios aimed at reducing infiltration. Hypothetical examples are presented to demonstrate potential applications of these solutions.