1. Modelling a Green Roof and the Benefits to Storm Water Management James Berryman 16th September 2010

2. Introduction Micro Drainage develop the industry-standard drainage design software in the UK and Ireland. Its WinDes® drainage design software is relied upon by engineers around the world, with over 14,000 software modules currently in use globally. WinDes allows engineers to design drainage solutions that meet the evolving challenges of flood management, environmental legislation, climate change and sustainability.

4. Urban heat sink

5. Aesthetic

6. Enhanced biodiversity

7. Improved insulation

8. Pollutant removal Final validation – Storm Water Management

9. Overcoming the Sceptics The What Ifs? Fair tests Drainage Standards Single storms (no tests for continuous analysis/Antecedent Conditions) New systems, no allowance for : FOG Sediment Root ingress Blockages (both internally and at inlets) Deformation

10. Specification Static Volumes v Real Time Analysis Pragmatic approach Two key variables to generate a runoff model Roof Area Substrate Depth

12. Two Forms of Storage Interception (Depression) Storage Depth of water that is retained in the roof (only lost through evapo-transpiration) Attenuation (Lag) Storage Conceptually equivalent to a unit hydrograph for the vertical flow through the substrate, the drainage layers and into the storm water network It was recognised that the total storage will vary with the Antecedent Dry Weather Period (ADWP)

13. Interception (Depression) Storage Field tests and other academic research (Pallaet al. 2008, Stovin et al. 2007, Denardoet al. 2004) indicated: That the retention to be expected after 2 days ADWP would provide a reasonably conservative perspective. An Interception value of 5% of substrate depth would be a reasonable average for an ADWP of 2 days.

14. Interception (Depression) Storage Applied 1ha Green Roof with 100mm of soil substrate applying a depression storage of 5% This will result in the first 5mm of rainfall being held in the roof Equating to 50m³ of storage Continuous Analysis and evapo-transpiration To scale

15. Attenuation (Lag) Storage Three Time Area Diagram (TAD) options were considered: Time Area Diagram 0-4 minute entry “Unit Hydrograph” (time to peak of 32 mins and a time base of 90 mins) Exponential

16. Calibration and Validation: i

17. Calibration and Validation: ii

18. Calibration and Validation: iii

19. Exponential Method Incorporated into WinDes A = factor required to scale the curve to provide the correct total catchment area e = exponential k = the decay coefficiency t = the time in minutes

20. Summary: Benefits for Storm Water Management? Consider a 2 ha warehouse roof discharging to storage tank. If a Green Roof is used the volume of storage reduces from 450m³ to 300m³ To scale

21. Further Research Future scope to calibrate the method: Varying roof construction materials /techniques More locations, slopes etc Increased/reduced lag affect? El Struthio

22. Contact Information James Berryman Tel: 01635 582555 james.berryman@microdrainage.co.uk Micro Drainage Ltd Jacobs Well West Street Newbury Berkshire RG14 1BD