Marie-Curie IAPP ‘Green Roof Systems’ Project
The Green Roof Research Conference 18-19 March 2013, Sheffield
Developing a new detention layer for extended runoff detention Fred Sonnenwald1, Ralf Walker2 1
University of Sheffield, f.sonnenwald@sheffield.ac.uk 2 ZinCo GmbH, ralf.walker@zinco-greenroof.com
Introduction Green roofs at field capacity offer little benefit as SUDS devices. They neither significantly delay nor attenuate run-off flow. All water passes through the roof quickly, which is disadvantageous in areas with high rainfall. While other parts of the project have focused on engineering plant choice or substrate to improve green roof quality, this work applies traditional engineering to improving hydraulic performance without impacting on other potential performance improvements. A new drainage layer has been developed to provide enhanced detention capabilities – a detention layer.
Overview of Methodology The new detention layer uses wicks to gradually empty a reservoir, shown in Figure 1. The properties of wicks were investigated in order to properly engineer a drainage layer which achieves the desired detention period of 24 to 48 hours. Controlled tests of wick flow rate were carried out using photographs and image analysis. The detention layer prototypes evolved as more information about wicks was and additional experience was used to improve design.
Figure 1 – Detention layer concept
Marie-Curie IAPP ‘Green Roof Systems’ Project
The Green Roof Research Conference 18-19 March 2013, Sheffield
Key Findings Wick performance can be predicted using reservoir routing. Wicks scale in parallel, and wick flow rate depends on rise (distance from water to top of reservoir), length of wick end (distance from top of reservoir to bottom of wick on free end), and bend (angle which wick goes through at top of the reservoir). Wick performance can be highly variable. Some wicks perform better than others, with more consistent performance and desirable flow rates. Wicks will not necessarily start from dry. A new wicking material was developed in order to achieve reliable performance. A prototype detention layer element (Prototype 3, Figure 2) is currently under testing. Test results have been used to predict performance for a 1-in-10 year Sheffield storm event, shown in Figure 3. The new element shows great potential towards enhancing SUDS performance of green roofs.
Figure 2 – Prototype 3
Flow (mm/minute)
7
Rainfall
6
Green roof
5
Detention Layer
4 3 2 1 0 0
20
40
60 Time (mm)
80
100
120
Figure 3 – Modelled detention layer performance compared to recorded green roof performance
Further Reading https://sites.google.com/a/sheffield.ac.uk/green-roof-research/ http://www.zinco-greenroof.com/