STUDY ON THE PERFORMANCE OF THE INFILTRATION STRATA BY NUMERICAL ANALYSIS

Abstract

Infiltration strata is an artificially devised soil structure used to reduce urban stormwater discharge. The major functions of this strata are 1) the passage of stormwater at the surface, 2) the retention of this water within the strata and 3) the exfiltration of this water into the natural base soil. We have developed a model to predict the behavior of stormwater within the strata, based on the numerical solution of Richards' Equation with appropriate soil property functions. This model was verified using the drainage data of column experiment. The predicted drainage volume was similar to that of observed one, but rapid changes in the drainage rate produced by changes in the rainfall rate were not adequately predicted. Hysteresis effect which makes the soil property functions irreversible and many-valued was introduced using the Mualem's model, and the rapid changes in the drainage rate could be well predicted. Using this model, the performance of the strata was simulated. Clearly the performance depended on the exfiltration rate into the natural base soil. The drainage infiltration strata, which has a drainage pipe at the bottom of the strata, could be effective when the rate of exfiltration into the natural soil is small.