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.

Engineered media used in living roofs and bioretention plays a crucial role in determining stormwater mitigation performance. Engineered media with compositions varying in four aggregates, volumetric ratio of compost (0, 10, and 20%) and three amendments (zeolite, paving sand, and topsoil) were prepared in the laboratory. Media basic properties including particle-size distribution (PSD), dry bulk density, particle density, porosity, and saturated hydraulic conductivity (Ks), were characterized and investigated as a function of the varying composition. All media are classified as poorly-graded sand (SP), exhibiting porosity greater than 0.51, with magnitudes of Ks ranging from 10−2 to 10−1 cm/s. Media with pumice-based aggregates have particle densities between 2.21 and 2.48 g/cm3. The Ks of a pure aggregate classified as SP is positively related to the particle size corresponding to 50% fines on the cumulative PSD curve. Ks values of four aggregates either remain unchanged or decrease by 73% at ...