Rapid infiltration measurement of lid best management practices

Infiltration is an essential process of most stormwater low impact development (LID) practices. Measurements of the infiltration capacity applied to a design storm are needed to determine performance, schedule maintenance and meet regulatory requirements. Infiltration rates, however, have great spatial variation and most existing infiltration measurement techniques are relatively slow and require a substantial amount of water. These measurements, therefore, are typically made at only one location. The Modified Philip-Dunne (MPD) infiltrometer is a new technique to measure the saturated hydraulic conductivity (K_sat) of the surface layer of a soil. It is a fast, simple and inexpensive falling head device; suitable for infiltration practices because it can be performed relatively quickly with minimal water to allow one the flexibility to capture the large spatial variability that occurs with infiltration capacities. A user-friendly spreadsheet program and a manual have made the application of the MPD infiltrometer straight-forward so that the infiltration capacity of soil can be obtained quickly. A comparison between the value of K_sat obtained from the MPD, from Double Ring Infiltrometer and from numerical simulations of the three-dimesional axisymmetric Richards equation for homogeneous and non-homogeneous soil will be presented. The MPD infiltrometer has been used in several LID practices, such as rain gardens, infiltration basins and swales. This method, developed for field application, has a simple experimental apparatus, straight-forward mathematical model and requires a small volume of water to perform the test.