Hydraulic Performance of Fully Permeable Highway Shoulder for Storm Water Runoff Management

Abstract

This paper summarizes the results of numerous simulations to assess the hydraulic performance of fully permeable highway shoulder retrofits designed to capture all the rainfall runoff falling onto conventional highway surface pavements. The simulations were performed using commercially available HYDRUS software that uses unsaturated flow theory. The hydraulic properties of subgrade soil and pavement materials were measured in the laboratory and used as input for numerical simulation. The simulations were performed for three rainfall regions in California representing high, medium, and low annual rainfall events. The simulations were performed based on 24-h actual rainfall data using 2-, 50-, and 100-year storm recurrences to determine the critical thickness of aggregate needed to capture the highway runoff volume without surface ponding and/or overflow. Sensitivity analyses were performed to evaluate the influence of material, hydrologic, and geometric factors on the critical aggregate base thickness. Results indicated that an aggregate depth of about 1.5 m was adequate for most California areas with two-lane highways. Sensitivity analyses also revealed that the saturated hydraulic conductivity (