A framework for comprehensive stormwater management practices in eastern and southern Australia

Transcription

1 A framework for comprehensive stormwater management practices in eastern and southern Australia John R Argue*, David Pezzaniti** and Guna Hewa *** *Adjunct Professor of Water Engineering ** Senior Research Engineer *** Lecturer in Civil & Water Engineering School of Natural & Built Environments Centre for Water Management & Re-use

2 STRUCTURE OF THE PRESENTATION Introduction A comprehensive WSUD framework: overall structure and Design Objectives Regional considerations A retention-based model (mathematical/hydrological): greenfield and developed catchment cases Implications and consequences: - volume retained - detention or retention? - storm successions and emptying time Conclusion Centre for Water Management & Re-use

3 INTRODUCTION: SEQ catchments: future directions? Centre for Water Management & Re-use

4 A COMPREHENSIVE WSUD FRAMEWORK Design Objectives - Floodplain:...quarantined from urban intrusion... - Frequent flow (low flows):...natural ecosystems are preserved following development... - Waterway stability:...natural ARI 1 2 year peak flow and hydrograph are preserved following development... - Stormwater infrastructure:...ari of highly-developed c ment infrastructure is preserved without the need for upgrade or augmentation for all time... - Stormwater quality:..measures that protect receiving waters.. - Stormwater harvesting:...max ise mains water replacement... Centre for Water Management & Re-use

5 A COMPREHENSIVE WSUD FRAMEWORK Performance Principles Background: statement...technical basis of the Design Objective Recommended Application: defines boundaries of the Design Objective... Demonstrating compliance: provides...specific technical information needed to convert the Design Objective into action. Centre for Water Management & Re-use

6 REGIONAL CONSIDERATIONS: Performance Principles Centre for Water Management & Re-use Northern Australia Zone i 10,1 70 mm/h Upper-Intermediate Zone 50 mm/h < i 10,1 < 70 mm/h Mid-Intermediate Zone 35 mm/h < i 10,1 < 50 mm/h Lower-Intermediate Zone 25 mm/h < i 10,1 < 35 mm/h Southern Australia Zone i 10,1 25 mm/h

7 A RETENTION-BASED MODEL : (mathematical/hydrological) Detention: refers to... holding of runoff for relatively short periods to reduce peak flow rate... discharge to downstream watercourses Retention: refers to procedures... stormwater is held for relatively long periods... domestic uses, infiltration, evaporation, transpiration...not, usually, discharge to downstream watercourses Urban Water Resources Centre

8 MATHEMATICAL/HYDROLOGICAL MODEL: greenfield catchments

9 MATHEMATICAL/HYDROLOGICAL MODEL: greenfield catchments Volume of stormwater passing from each catchment element before development (ARI,1 2 yrs)...must equal... volume discharged from the same catchment elements following development in the design storm of critical duration

10 MATHEMATICAL/HYDROLOGICAL MODEL: greenfield catchments

11 MATHEMATICAL/HYDROLOGICAL MODEL: greenfield catchmentshments The volume retained: USE IT! Domestic uses; open space irrigation, etc Soil moisture enhancement ( soakaways, garden beds, etc) Aquifer recharge; deep percolation... baseflow to local waterways; Volume left over slow drainage to waterways in manner of extended detention Centre for Water Management & Re-use

12 MATHEMATICAL/HYDROLOGICAL MODEL: greenfield catchments CONCLUSION: Greenfield developments Equal before and after (development) surface runoff volumes delivered to the drainage path at each catchment element will result in before and after (total) runoff hydrographs with similar characteristics of peak flow and shape (ARI,1-2 yrs) Hence, any level of development can occur in a greenfield catchment... without significantly changing the main characteristics of the flood runoff hydrograph it possessed (ARI, 1 2 years)...in its natural state. Centre for Water Management & Re-use

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14 MATHEMATICAL/HYDROLOGICAL MODEL: developed catchment experiencing re-development

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16 MATHEMATICAL/HYDROLOGICAL MODEL: developed catchment experiencing re-development Volume of stormwater passing from each catchment element before redevelopment (ARI, Y years)...must equal... volume discharged from the same catchment elements following re-development in the design storm of critical duration

17 MATHEMATICAL/HYDROLOGICAL MODEL: developed catchment experiencing re-development

18 MATHEMATICAL/HYDROLOGICAL MODEL: developed catchment experiencing re-development The volume retained: USE IT! Residential/industrial/commercial uses; open space irrigation, etc Roof gardens, green roofs; Water features; ornamental lakes; Aquifer recharge; Volume left over slow drainage to waterways in manner of extended detention

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20 MATHEMATICAL/HYDROLOGICAL MODEL: developed catchment experiencing re-development CONCLUSION: Re-development in urban catchment Equal before and after (re-development) surface runoff volumes delivered to the drainage path at each catchment element will result in before and after (total) runoff hydrographs with similar characteristics of peak flow and shape. Hence, an existing, competently-performing, formal stormwater infrastructure (ARI, Y-years) can continue to operate satisfactorily without restriction on the level of re-development imposed and without the need for enlargement or augmentation for all time. Centre for Water Management & Re-use

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22 IMPLICATIONS AND CONSEQUENCES: 1. Volume retained Stormwater harvesting: Design Objective No 6; Stormwater quality improvement: part of retained volume can be assigned to bio-retention facilities and wetlands (Design Objective No 5); Stormwater quantity management: channelforming flows etc (Design Objective No 3) and flood control (Design Objective No 4); Floodplain delineation: quantity control with development (Design Objective No 1); Frequent flows (low flows): Design Objective No 2; Final option: release downstream at low flow rate. Centre for Water Management & Re-use

23 IMPLICATIONS AND CONSEQUENCES: 2. Detention or Retention? 4 5 e 2 d c b 1 a O e 500m 2 c d 500m 500m b 500m 1 a 500m O 3

24 Centre for Water Managemednt & Re-use Erosion Potential Index, EPI with detention basins (EPI ~ 6) Pre-development Post-development with detention basins Peak 7.11 m 3 /s At b 6-fold increase Peak: 7.72 m 3 /s 8-fold increase Peak 8.43 m 3 /s At O 6-fold increase Peak: 9.68 m 3 /s 8-fold increase

25 Erosion Potential Index, EPI with retention practice (EPI ~1.5) Pre-development Post-development with retention practice Peak: 7.71 m 3 /s At b Peak: 7.71 m 3 /s Peak; 8.43 m 3 /s At O Peak; 8.43 m 3 /s

26 IMPLICATIONS AND CONSEQUENCES: 3. Storm successions and emptying time Storages must be empty before the arrival of the next significant storm. Achievement of this (design) requirement calls for use of continuous simulation modelling. An alternative is to use the emptying time criteria set out in the WSUD Handbook - Ave Recurr. Interval (ARI), Y-years Emptying time, T in days 1-year or less 2- years 5- years 10- years 20- years 50- years 100- years

27 CONCLUSION This presentation has offered some thoughts on the comprehensive framework that is needed to manage the various stages of development and redevelopment that can be expected to occur in eastern and southern Australia in the decades and centuries ahead. The framework is strongly influenced by retention principles interpreted into a mathematical/hydrological model which provides not only a basis for implementing sound environmental practices in greenfield settings but is, also, environmentally positive and cost-effective when applied to re-development scenarios in landscapes already highly urbanised.