Determination of Unsaturated Hydraulic Properties for Low Impact Developments

ABSTRACT: With the increase in extreme rainfall events and rapid urbanization, the risk of flooding has increased substantially. Low Impact Developments (LIDs) can assist in decreasing this risk within certain areas. The soil is generally considered to be completely saturated when designing for the LIDs. However, this may not always be an accurate or realistic approach, as the soil could be variably unsaturated leading to inaccurate designs. To analyze the flow under variably unsaturated conditions, Richards’ equation can be used. In order to solve the Richards’ equation, two nonlinear hydraulic properties namely, soil water characteristic curve (SWCC) and the unsaturated hydraulic conductivity function are required. Laboratory and field measurements of unsaturated hydraulic properties are cumbersome, expensive and time-consuming. An alternative approach is to estimate unsaturated hydraulic properties using pedotransfer functions. Pedotransfer functions estimate soil hydraulic properties using routinely measured soil properties, such as soil texture, grain size distribution, bulk density, or porosity. This research presents a comparison between the direct measurement obtained through experimental procedures and the use of pedotransfer functions to estimate soil hydraulic properties for two green roof and three bioretention soil medias. Design implications are also part of this research effort.