Hydraulic Properties of Bioretention Mixes.

Bioretention media are usually engineered systems designed to modulate the stormwater hydrograph and to remove and attenuate contaminants from stormwater. Many different media mixes and designs are in use, and research is ongoing to find optimal media mixes and designs. An optimal bioretention system to remove pollutants from stormwater should have a high capacity to retain a variety of pollutants and, at the same time, should let the water permeate through the system. Several mesocosms (zero-tension lysimeters) were filled with different types of bioretention mixes in 2010. The mixes consisted of different mixes of sand, compost, and biochar. We determined hydraulic properties, i.e., water retention characteristics and hydraulic conductivities, of these mixes and monitored the temporal evolution of hydraulic conductivities. Water content and water potentials were also measured in situ and compared with laboratory measured water retention data. Compost and biochar amendments increased hydraulic conductivity and water holding capacity. Hydraulic properties remained stable over the 4-years of monitoring.