Application of a Conceptual Hydrological Model to Identify the Impacts of Green Roof Substrate Ageing on Detention Performance

The substrate within a green roof is subject to numerous natural processes throughout its intended design life. As such there is a need to identify the impacts these processes have on substrate hydrological performance over time. Presented is a conceptual hydrological green roof model that utilises non-linear reservoir routing techniques to parameterise detention processes into scale, k and exponent, n. The value of n can be fixed as it largely influenced by the roofs construction (roof slope, drainage length, etc.), thus reducing the model to a single parameter, k. Using observed rainfall/runoff data from test beds at The University of Sheffield values of k were identified for a series of 25 events over a period of 4 years. A rise in the mean value of k was observed for each year of the study, indicating a reduction in detention performance. A design storm exercise allows for the changes in detention performance to be quantified in commonly reported detention metrics.