609-621 Burwood Highway Expert Opinion on Stormwater Management Strategy for Fast Track Government Land Service
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Evidenced by Glenn Ottrey requested by Development Victoria 609-621 Burwood Highway Expert opinion on stormwater management strategy for fast track government land service 2 March 2018 V6000_002 EVIDENCED BY GLENN OTTREY REQUESTED BY DEVELOPMENT VICTORIA 609-621 BURWOOD HIGHWAY CONTENTS 1. INTRODUCTION .......................................................................................................3 2. THE SUBJECT SITE .................................................................................................4 2.1 Subject Site ...............................................................................................................4 3. REFERENCE DOCUMENTS .....................................................................................5 4. ASSESSMENT ..........................................................................................................6 4.1 Stormwater quantity management .............................................................................6 4.2 Stormwater quality management ...............................................................................6 4.3 Flood modelling of Blind Creek ..................................................................................7 4.4 Existing dam ..............................................................................................................8 5. STATEMENT ........................................................................................................... 10 Appendices APPENDIX A – GLENN OTTREY DETAILS, CURRICULUM VITAE AND INSTRUCTIONS APPENDIX B – WETLAND FUNCTIONAL DESIGN PLANS APPENDIX C – FLOOD MAPS APPENDIX D – DAM CONDITION ASSESSMENT REPORT Job No. V6000_002 Page ii : 02/03/2018 EVIDENCED BY GLENN OTTREY REQUESTED BY DEVELOPMENT VICTORIA 609-621 BURWOOD HIGHWAY 1. INTRODUCTION This report provides expert evidence by Glenn Ottrey as requested by Development Victoria. This report relates to the proposed preliminary stormwater management strategy for 609-621 Burwood Highway in Knoxfield. The stormwater strategy has been described as a preliminary strategy as the masterplan for the site has not yet been developed. The stormwater management strategy will be further refined once the masterplan is developed, however it is not expected that there would be any significant changes required to the stormwater management strategy. Details of the report author and contributors are provided in Appendix A. Job No. V6000_002 Page 3 : 02/03/2018 EVIDENCED BY GLENN OTTREY REQUESTED BY DEVELOPMENT VICTORIA 609-621 BURWOOD HIGHWAY 2. THE SUBJECT SITE This report is based on information provided to me listed as the reference documents in section 3, as well as a site visit undertaken by me and Andrew Prout on Wednesday 16 November 2016. 2.1 Subject Site The subject site is located in Knoxfield in the City of Knox. A locality plan showing the property is provided in Figure 3-1. Figure 2-1 Locality Plan Job No. V6000_002 Page 4 : 02/03/2018 EVIDENCED BY GLENN OTTREY REQUESTED BY DEVELOPMENT VICTORIA 609-621 BURWOOD HIGHWAY 3. REFERENCE DOCUMENTS The following documents and information has been supplied to or sourced by Engeny and has been used to inform the preliminary stormwater management plan. ▪ CSIRO 1999, Urban Stormwater Best Practice Environmental Management Guidelines (BPEMG) ▪ Ecocentric Environmental Consulting 2015, Preliminary Biodiversity Assessment 609- 619 & 621 Burwood Highway Knoxfield ▪ Ecocentric Environmental Consulting 2017 Flora, Fauna and Native Vegetation Assessment 609-619 & 621 Burwood Highway Knoxfield ▪ Engeny, 2017 Dam Condition Assessment Report – 621 Burwood Highway, Knoxfield ▪ Feature and level survey, including dam bathymetry by CRA Survey Pty Ltd version 3 dated 20-07-2017 ▪ GHD 2015, 621 Burwood Highway, Knoxfield Development Assessment ▪ GIS asset data of underground drains provided by Melbourne Water ▪ Knox 5 year MUSIC rainfall template file “Knox City Council - 5 Year 6 Minute Rainfall Template.mlb” ▪ LiDAR data sourced from the Department of Environment Land Water and Planning ▪ Planning Panel’s Victoria “Guide to Expert Evidence” ▪ RORB hydrologic model of Blind Creek provided by Melbourne Water on 22-06-2017 ▪ Stormwater drainage guidelines for residential, commercial, industrial and broad acre subdivisional developments, City of Knox, May 2006 (currently available from the City of Knox website https://www.knox.vic.gov.au/Files/Roads/StormwaterDrainageGuidelines.pdf) ▪ The Royal Life Saving Society Australia, 2004, Royal Life Saving Guidelines for Water Safety in Urban Water Developments Job No. V6000_002 Page 5 : 02/03/2018 EVIDENCED BY GLENN OTTREY REQUESTED BY DEVELOPMENT VICTORIA 609-621 BURWOOD HIGHWAY 4. ASSESSMENT I have led the preparation of the preliminary stormwater management plan for 609-621 Burwood Highway Knoxfield. This report is titled “621 Burwood Highway Knoxfield, Preliminary stormwater management plan, Revision 7, dated 3 August 2017”. This report details the proposed management of stormwater as the site is developed. A summary of the key points in the report is contained below. 4.1 Stormwater quantity management A summary of key points regarding to stormwater quantity management is: ▪ A minor (piped) drainage system sized for the 5 year average recurrence interval (ARI) event, in line with the City of Knox stormwater drainage guidelines. • Since the issue of the preliminary stormwater management strategy, I have spoken to Neils Unger, drainage engineer at the City of Knox, who has requested a 10 year ARI drainage design standard for the piped system. This can be accommodated with no change in the proposed zoning and overlays. ▪ The major stormwater drainage system sized to convey the gap flow between the capacity of the minor drainage design system and flows in the 100 year ARI event. ▪ A RORB hydrologic model was developed to determine the required size of the retarding basin to ensure that peak flows discharging from the site were not increased in the 100 year ARI event in developed conditions compared to existing conditions. The retarding impact of the existing dam was considered as part of the development of this modelling. • The RORB modelling showed that the current 100 year ARI peak flow from the site is 3.6 m3/s under existing conditions and under the proposed development conditions it would be 3.5 m3/s. 4.2 Stormwater quality management A summary of the key points relating to stormwater quality management is: ▪ Stormwater will need to be treated to Best Management Practices as required by Clause 56.07-4 of the Victoria Planning Provisions. ▪ Stormwater treatment for the entire site is proposed to be achieved in a single location through a combined sedimentation basin and wetland. ▪ MUSIC modelling of the proposed stormwater treatment system shows that a 1100 m2 sedimentation basin and 4500 m2 stormwater treatment wetland are able to meet the best practice targets for the development area. Job No. V6000_002 Page 6 : 02/03/2018 EVIDENCED BY GLENN OTTREY REQUESTED BY DEVELOPMENT VICTORIA 609-621 BURWOOD HIGHWAY • Since the issue of the preliminary stormwater management strategy, I have spoken to Neils Unger, drainage engineer at the City of Knox, who has requested that the MUSIC model be run with the Knox MUSIC rainfall template. I have run the MUSIC model with the Knox MUSIC template and it meets the best practice targets with no changes to any of the other model parameters (apart from the rainfall), including wetland or sedimentation basin sizes. ▪ 10,400 m2 of additional habitat wetland is also provided. Stormwater entering the habitat wetland will first be treated in the sedimentation pond and the stormwater treatment wetland to improve the quality of the stormwater entering the habitat wetland ▪ Construction could be staged so that the habitat wetland is constructed prior to the removal of the existing dam ▪ A functional design of the wetland has been undertaken to demonstrate that the required treatment areas can physically be achieved within the proposed footprint. The functional design plans are shown in Appendix B. ▪ Consideration could be given to utilising the wetland system for stormwater harvesting to provide water for irrigation. 4.3 Flood modelling of Blind Creek A summary of the key points relating to the flood modelling on Blind Creek is: ▪ Blind Creek is a Melbourne Water managed waterway. At the request of Melbourne Water, Engeny created a two-dimensional hydraulic model (TUFLOW) of Blind Creek adjacent to the development area to assess the impact of the proposed development on flood levels within and adjacent to the creek. ▪ Melbourne Water provided a RORB model of the Blind Creek catchment, which was used to provide inflow hydrographs for the TUFLOW modelling. ▪ Based on the RORB model, the critical duration event for the 100 year ARI storm for Blind Creek adjacent to the development location is the 2 hour duration storm, which has a peak flow rate of 41.8 m3/s. ▪ The TUFLOW model was validated against flood levels provided by Melbourne Water. The results for the existing conditions model were 60 mm and 30 mm higher than the flood levels provided by Melbourne Water at the north west and north east corners of the subject site, which represents a good and slightly conservative match to the information provided by Melbourne Water. ▪ The modelling assumed that the dam was full to spillway level at the time of the storm event as there is no low flow outlet which can be relied upon to drain the dam and provide additional floodplain storage.