Veranstaltungsprogramm

Stormwater engineers need to predict how Low Impact Development (LID) assets (e.g. green roofs and bioretention cells) respond to both routine and extreme rainfall events. Typically, the growing media of the LID assets will be in an unsaturated state, where percolation through the media is related to the media’s volumetric water content. This relationship can provide significant detention effects, particularly when moisture contents are at or near field capacity. Correctly representing these unsaturated flows is critical to ensuring robust long-term continuous simulations of bioretention hydrological performance. The US EPA’s Storm Water Management Model, SWMM, is the most well-known of the available open-source modelling tools. SWMM models the percolation rate in the growing media with an exponential function. The resulting percolation estimates have been observed to lead to poor modelled outflow responses during low flow conditions.

This study introduces a new power form Hydraulic Conductivity Function (HCF) that better represents observed percolation rates and yields improved modelled outflow responses. Crucially, the New HCF requires the same number of media specific variables as the current SWMM HCF. Even with these HCF improvements, modelled outflow timings are still compromised by the homogenous media moisture content assumed within the SWMM percolation model framework.