Ponded Infiltration From a Single Ring: I. Analysis of Steady Flow

Abstract A new analysis of steady, ponded infiltration from within a single ring takes soil hydraulic properties, ring radius, depth of ring insertion, and depth of ponding into account. It also provides a means for determining the field‐saturated hydraulic conductivity ( K fs ) and the matric flux potential (φ m ). The analysis employs numerically determined shape factors ( G ) that are found to depend significantly on ring radius ( a ) and depth of ring insertion ( d ), but only slightly on depth of ponding ( H ) and soil hydraulic properties. As a consequence, averaged G values ( G e ) can be developed for specified d and a that apply to a wide range of ponded heads and soil types. Procedures for calculating K fs and φ m are based on G or G e , and on the ponding of one, two, or multiple H levels in the ring. Test calculations based on G e suggest that K fs can be obtained with an accuracy of about ±20% for H = 0.05 to 0.25 m and α = 1 to 36 m −1 , where α is the soil parameter of the exponential hydraulic conductivity‐pressure head relationship. A similar level of accuracy (using G e ) is obtained for φ m when α is small (α ≤ 4 m −1 ), and when both α and H are large (α > 4 m −1 , H ≥ 0.20 m). Significant errors in φ m can occur, however, when α is large but H is small. Potentially important features of this single ring method include low sensitivity of the K fs calculation to errors in G e , reduced measurement errors resulting from small‐scale soil variability, and the ability to pond large heads in order to increase flow rates in low‐permeability materials.