Design of Circular Infiltration Basin under Mounding Effects

Abstract

The operation of an infiltration basin is jointly controlled by the infiltration at the land surface and the seepage through the subsurface medium. When the operation of the basin is under a back pressure due to water mounding effects, it takes a prolonged drain time and may cause a failure. This phenomenon becomes more pronounced when the land surface infiltration is greater than the subsurface soil permeability. When selecting a basin site, it is important to assess its subsurface hydraulic adequacy relative to the design infiltration capacity. This study presents a downward axisymmetric stream function by which the required subsurface geometry underneath a circular infiltration basin can be quantified. The infiltrating flow through the unsaturated zone to the ground-water table can be depicted by this potential flow model with the consideration of anisotropic permeability and water mounding at the ground-water table. The required subsurface geometry underneath a basin is found to be related to the radius of the basin, and the required saturation depth is proportional to the ratio of infiltration rate to coefficient of permeability. This model can assist engineers to establish a quantifiable basis to compare and to select a basin site without detailed site specifics.