Hydrological response of a volcanic medium as a potential substrate for green roofs

This study aimed at evaluating the hydrological response of a volcanic medium (VM) obtained from ash deposition that followed the recent eruptions of Mount Etna (Italy). Due to its lightness and sustainability, this material appears appropriate for preparing “engineered soils” suitable as substrates for green roofs. Simulated rainfall experiments were conducted on microcosms to assess both detention and retention capacities of VM under dynamic conditions. Furthermore, to improve the physical and hydraulic properties of VM, the particle distribution was graded by artificially increasing or decreasing the coarse fraction. Starting from initial dry conditions, the green roof was able to detain from 19.3% to 46.0% of the total rain volume in line with the results of the literature. When initial wet conditions were considered, detention was reduced but anyway in the order of 10% of the total rainfall. Decreasing the VM coarse fraction reduced the distribution of macroporosity and increased that of mesoporosity thus enhancing the drainable water capacity with positive effects on the substrate’s detention capacity.