Pore Structure and Unsaturated Hydraulic Conductivity of Engineered Media for Living Roofs and Bioretention Based on Water Retention Data

Characterizing pore structure and hydraulic properties of engineered media used in stormwater control measures (e.g., green roofs and bioretention) is critical for accurately predicting water and contaminant flow characteristics, water availability to plants, and aeration status. In this study, unsaturated hydraulic properties, namely, the water retention characteristic (WRC) and unsaturated hydraulic conductivity (K), were measured for 14 engineered media with varying compositions. Their WRCs were also used to investigate pore structures and estimate hydraulic conductivities. Results indicate that water retention dynamics in 10 pumice-based media involve complex interactions between interaggregate and intra-aggregate pores, for which the commonly used van Genuchten function is not suitable. The majority of the pores in the tested media have radii less than 1 mm, for which the Richards equation is applicable. A predictive K function based on WRC and Mualem’s approach tends to underestimate K at low water contents. More research is needed to study hydrological behavior of engineered media with complex pore systems under various flow conditions.