Hydraulic conductivity and impact on retrofit stormwater biofiltration - case study of the design, assessment and function of retrofit raingardens using different filter media in Sydney

This paper presents a case study of the design and performance of various biofiltration systems using different filter media and different methods to measure hydraulic conductivity. Modelling undertaken as part of this study indicated that for small systems a high hydraulic conductivity will result in a better overall performance. Assessment of the hydraulic performance of four biofiltration systems was carried out using two different methods, both using a single ring infiltrometer but using different formulas to calculate the hydraulic conductivity. The results showed that biofiltration using sandy loam reported significantly lower hydraulic conductivity using both methods than that previously reported in laboratory tests. In all testing there was great variability in the results suggesting the need for caution to rely on any single test or method to accurately report the hydraulic conductivity. From a design and operational perspective this study supports the use of sand over sandy loam as a filter media particularly where there is insufficient space to size the biofiltration system according to best practice guidelines.