Brian L. Taylor, P.E., and Drew A. Gangnes, P.E. - Green Roofs for ...

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Coordination with the City of Seattle to accept this approach and model is currently underway. It isMKA’s opinion that the assumptions in these studies are conservative; additional data from on-goingmonitoring and research programs is expected to support relaxing some of the conservative inputparameters. In addition to results presented, preliminary modeling for case studies indicates thatimplementing eco-roofs with other practices, such as roof ponding, could eliminate the need forunderground detention tanks, pumps, and pipes, as well as increase the portion of eco-roof costspotentially offset by detention tank costs savings to over 50 percent (20).RECOMMENDATIONSMonitoring, demonstration projects, and research are needed to support further calibration andrefinement of this and other eco-roof models. These data could allow conservative assumptions to berelaxed, improving the detention cost offsets provided by eco-roofs. Development of a continuous ecoroofhydrology model would allow more sophisticated analyses, account for specific weather patterns ata project site, and facilitate acceptance of eco-roof stormwater benefits by certain agencies.REFERENCES1. Hutchinson, D., Abrams, P., Retzlaff, R., and Liptan, T., Stormwater Monitoring Two Ecoroofs inPortland, Oregon, USA, Proceedings of Greening Rooftops for Sustainable Communities: Chicago2003.2. Miller, Charlie, Vegetated Roof Covers: A New Method for Controlling Runoff in Urbanized Areas,Proceedings of the 1998 Pennsylvania Stormwater Management Symposium, Villanova University, 1998.3. City of Seattle Title 22.800 Stormwater, Grading, and Drainage Control Code, Volume 3: FlowControl Technical Requirements Manual, November 2000.4. King County Surface Water Design Manual, King County Surface Water Management Division,1990.5. Stormwater Management Manual for the Puget Sound Basin, Washington Department of Ecology,1992.6. Stormwater Management Manual for Western Washington, Washington Department of Ecology,2001.7. Miller, Charlie, Approach for Analysis of Green Roof Runoff, Roofscapes, Inc.8. Graham, P. and Kim, M., Evaluating the Stormwater Management Benefits of Green Roofs ThroughWater Balance Modeling, Proceedings of Greening Rooftops for Sustainable Communities: Chicago2003.9. Mentens, J., Raes, D., and Hermy, M., Effect of Orientation on the Water Balance of Greenroofs,Proceedings of Greening Rooftops for Sustainable Communities: Chicago 2003.Method for Quantifying Runoff Reduction of Green RoofsBrian L. Taylor, P.E., and Drew A. Gangnes, P.E.9
10. Liptan, T., City of Portland, telephone conversation on March 9, 2004.11. Miller, Charlie, Moisture Management in Green Roofs, Proceedings of Greening Rooftops forSustainable Communities: Chicago 2003.12. Gregory, M., Cunningham, B., Schmidt, M., and Mack, B., Estimating Soil Storage Capacity forStormwater Modeling Applications, 6th Biennial Stormwater Research and Watershed ManagementConference, September 14-17, Tampa, Florida, 1999.13. United States Department of Agriculture, Soil Conservation Service, TR55: Urban Hydrology forSmall Watersheds, Second Edition, 1986.14. United States Department of Agriculture, Soil Conservation Service, National EngineeringHandbook, Section 4 “Hydrology,” 1985.15. United States Department of Agriculture, Soil Conservation Service, TR-20 Hydrology TechnicalNote 2, “Chapter 1: The Modified Att-Kin Routing Model,” 1986.16. Magnusson Klemencic Associates, “Model Calibration and Validation using Portland Eco-roofMonitoring Data,” unpublished draft technical memorandum, March 2004.17. Magnusson Klemencic Associates, “Identifying Antecedent Moisture Inherent in Western WashingtonCurve Numbers,” unpublished draft technical memorandum, March 2004.18. Zimmer, U., and Geiger, W.F., Model for the Design of Multi-layered Infiltration Systems, Wat. Sci.Tech., Vol. 35, No. 8-9, pp. 301, 1997.19. Cedergren, H., Seepage, Drainage, and Flow Nets, John Wiley & Sons, 1989.20. Magnusson Klemencic Associates, “Case Studies for Offsetting Underground Detention Costs byusing Rooftop Runoff Management Practices,” unpublished draft technical memorandum, March 2004.TECHNICAL APPENDIXTHEORETICAL ATT-KIN STORAGE COEFFICIENT FOR ECO-ROOFSBased on the derivation of the routing coefficient used in the SBUH model (15), and published literatureabout drained porous media (18, 19), a storage coefficient for eco-roofs can be derived. Specific unitconversions are omitted in the equations below, instead generic length [L] and time [T] dimensions areshown.From the original Att-Kin routing method derivation (15), the storage coefficient (K) is defined to be therelationship between the storage (S) and discharge (O) for a basin:(Eqn. A1) S = K*O [L3]Method for Quantifying Runoff Reduction of Green RoofsBrian L. Taylor, P.E., and Drew A. Gangnes, P.E.10
Page 1: METHOD FOR QUANTIFYING RUNOFFREDUCT
Page 4 and 5: INTRODUCTIONGreen roofs, also known
Page 6 and 7: NEW APPROACH TO MODELING MODEL SITE
Page 8 and 9: initial infiltration processes (13)
Page 10 and 11: CASE STUDIESCase studies of existin
Page 14: For a freely drained media the disc

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