Effective Saturated Hydraulic Conductivity of an Infiltration-based Stormwater Control Measure

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Infiltration rates into field soils have a large variability, and a statistical value that represents the overall infiltration in a site is needed. The Green-Ampt equation was used to develop a one-dimensional, multisoil model to predict the water surface drawdown in an infiltration-based stormwater control measure (SCM) as a function of time. Results were used to compare the accuracy of assuming the SCM was comprised of a single soil with an overall effective saturated hydraulic conductivity set equal to (1) the geometric mean of the spatially distributed hydraulic conductivity values of the multisoil SCM, (2) the arithmetic mean of the hydraulic conductivity values, and (3) a best-fit hydraulic conductivity value. Results indicated that the use of the geometric mean consistently underestimated infiltration and use of the arithmetic mean consistently overestimated infiltration. A relationship to more consistently and accurately predict the best-fit value of saturated hydraulic conductivity used a weighted sum of 0.32 times the arithmetic mean and 0.68 times the geometric mean.