Willoughby Flood Management Conditions

13. Submit the Following Information to Willoughby City Council Prior to the lodgement of an application for a construction certificate, the applicant shall submit plans and specifications satisfying the following requirements to Willoughby City Council for approval. Documentation confirming approval by Willoughby City Council shall then be submitted to the Certifier for the application of a construction certificate. (a) Detailed stormwater plans for the site that include the following information: • Detailed design for OSD tank, including overflow levels. The overflow levels are to be through the top or side of the tank and are to be to ground and not to a pipe or internal chamber with a…

20. Driveway Longsection Prior to issue of the Construction Certificate for each Stage and in order to assess the susceptibility of vehicles to scraping as they pass over the proposed access driveway the applicant shall submit longitudinal sections for approval by the certifying authority along each side of the proposed vehicular access path drawn at 1:20 Scale. The longitudinal sections shall include the following: - (a) Horizontal distance from the centreline of the road to the proposed parking slab, including provision of Council’s standard layback as per Council’s standard drawing SD105 which is available from Council’s website. Council’s standard layback is 500mm wide and back of…

105. Flood Certification Prior to the issue of an Occupation Certificate for Stage 1 and Stage 2, submit to Council written certification, prepared by a suitably qualified and experienced civil engineer (generally CPEng), that the as-constructed works comply with the recommendations of Calibre’s Hydrology and Hydraulic Analysis for the site dated 30 July 2021 and that: - The as-constructed finished floor levels have 500mm freeboard to the 1%AEP flood level. - That the access ramp to the basement is at or above the adjacent PMF flood level. (Reason: Ensure compliance and prevent flood damage) 106. 88E Restriction – Affordable Housing Pursuant to the Environmental Planning and Assessment…

13. Basement Pumpout Drainage System Prior to the issue of the Construction Certificate, the applicant shall submit, for approval by the Certifier, detailed stormwater management plans in relation to the pump-out drainage system. The construction drawings and specifications shall be generally in accordance with the approved stormwater management plans with the following requirements: (a) The pumpout drainage system shall comprise with two (2) submersible type pumps. The two pumps shall be designed to work on an alternative basis to ensure both pumps receive equal use and neither remains continuously idle. (b) Each pump shall have a minimum capacity of 10L/s or shall be based on the flow…

13. Basement Pumpout Drainage System Reference: DA-2023/256 Page 11 of 59 PPSSNH-433 Prior to the issue of the Construction Certificate, the applicant shall submit, for approval by the Certifier, detailed stormwater management plans in relation to the pump-out drainage system. The construction drawings and specifications shall be generally in accordance with the approved stormwater management plans with the following requirements: (a) The pumpout drainage system shall comprise with two (2) submersible type pumps. The two pumps shall be designed to work on an alternative basis to ensure both pumps receive equal use and neither remains continuously idle. (b) Each pump shall have a minimum…

25. Basement Pumpout Drainage System Prior to the issue of the Construction Certificate, the applicant shall submit, for approval by the Certifier, detailed stormwater management plans in relation to the pump-out drainage system. The construction drawings and specifications shall be generally in accordance with the approved stormwater management plans with the following requirements: (a) The pumpout drainage system shall comprise with two (2) submersible type pumps. The two pumps shall be designed to work on an alternative basis to ensure both pumps receive equal use and neither remains continuously idle. (b) Each pump shall have a minimum capacity of 10L/s or shall be based on the flow…

30. Basement Pumpout Drainage System Prior to the issue of the Construction Certificate, the applicant shall submit, for approval by the Certifier, detailed stormwater management plans in relation to the pump-out drainage system. The construction drawings and specifications shall be generally in accordance with the approved stormwater management plans with the following requirements: (a) The pumpout drainage system shall comprise with two (2) submersible type pumps. The two pumps shall be designed to work on an alternative basis to ensure both pumps receive equal use and neither remains continuously idle. (b) Each pump shall have a minimum capacity of 10L/s or shall be based on the flow…

15. Basement Pumpout Drainage System Prior to the issue of the Construction Certificate, the applicant shall submit, for approval by the Certifier, detailed stormwater management plans in relation to the pump-out drainage system. The construction drawings and specifications shall be generally in accordance with the approved stormwater management plans with the following requirements: (a) The pumpout drainage system shall comprise with two (2) submersible type pumps. The two pumps shall be designed to work on an alternative basis to ensure both pumps receive equal use and neither remains continuously idle. (b) Each pump shall have a minimum capacity of 10L/s or shall be based on the flow…

14. Amended Stormwater Plans Amended stormwater plans must be submitted for approval with the Construction Certificate that demonstrate the following: (a) That a maximum of 5% of the impervious area is allowed to bypass the Stage 1 eastern detention tank (OSD1), with the discharge to be confirmed that in the 1%AEP storm event the peak flow leaving the site does not exceed the permitted site discharge (PSD) as detailed in Technical Standard 1. (b) To ensure adequate safety and maintenance, OSD Tank 2 must show access points into the tank at the outlet and at the opposite corner of the tank. (c) To meet water quality targets in line with DCP Part I, stormwater runoff from all parking areas,…

12. Detailed Stormwater Management Plan (SWMP) Prior to the issue of the Construction Certificate, submit to the Certifier for approval, detailed stormwater management plans in relation to the on-site stormwater management and disposal system for the development. The construction drawings and specifications shall be prepared by a suitably qualified and experienced civil engineer and be in accordance with Telford Civil’s drawings 101/C, 102/C, 104/C, 105/C, 106/D, 107/B, 108/E, 109/D, 110/C. The plans shall be amended to show that the outlet from the OSD tank has a minimum level of RL 99.20m. Alternatively, details must be submitted to Council and approval gained from Council to demonstrate…

24. Detailed Stormwater Management Plan (SWMP) Prior to the issue of the Construction Certificate, submit to the Certifier for approval, detailed stormwater management plans in relation to the on-site stormwater management and disposal system for the development. The construction drawings and specifications shall be prepared by a suitably qualified and experienced civil engineer and be in accordance with Telford Civil drawings 23190 101/B, 102/A, 103/B, 104/E, 105/B, 105.1/B and 106/A. The plans shall be amended so that the overflow from the OSD tank is to ground and not to an underground channel / chamber pipe. The overflow shall be in a visible location and have a minimum of 300mm…

77. On-site Water Management System Prior to the issue of any Occupation Certificate, the stormwater runoff from the site shall be collected and disposed of via an approved OSD and water quality improvement system in accordance with Sydney Water’s requirements AS/NZS3500.3, Council’s DCP and Technical Standards. The construction of the stormwater drainage system of the proposed development shall be in accordance with the approved detailed stormwater drawings required under this development consent and Council’s specification (AUS-SPEC). The system shall include an OSD system for all impervious areas in accordance with the requirements of Technical Standard 1. The drainage system is to…

29. Detailed Stormwater Management Plan (SWMP) Prior to the issue of the Construction Certificate, submit to the Certifier for approval, detailed stormwater management plans in relation to the on-site stormwater management and disposal system for the development. The construction drawings and specifications shall be prepared by a suitably qualified and experienced civil engineer and in accordance with the concept stormwater management plans, prepared by EI Australia. All drawings shall comply with Part I of Council’s Development Control Plan and Technical Standard 1, AS/NSZ3500.3 – Plumbing and Drainage Code and National Construction Code. If the catchment area of the OSD tank is not able…

4. Submit the Following Information to Willoughby City Council Prior to the lodgement of an application for a construction certificate, the applicant shall submit plans and specifications satisfying the following requirements to Willoughby City Council for approval. Documentation confirming approval by Reference: DA-2024/106 Page 5 of 78 Willoughby City Council shall then be submitted to the Certifier for the application of a construction certificate. (a) Revised stormwater management plans that clearly show the overflow from the OSD tank to ground and not to an underground channel or piped system. The overflow must be in a visible location and have the required 300mm freeboard to adjacent…

109. On-site Water Management System Prior to the issue of any Occupation Certificate, the stormwater runoff from the site shall be collected and disposed of to the Council stormwater pit in Hammond Lane via a water quality improvement system and an approved OSD system with a minimum volume of 45m3 that limits the peak stormwater flow from the site in the 1%AEP storm event to 20.1L/s. The system shall be in accordance with AS/NZS3500.3, Part I of Council’s DCP and Technical Standards 1 and 2. The construction of the stormwater Reference: DA-2023/256 Page 44 of 59 PPSSNH-433 drainage system of the proposed development shall be in accordance with the approved detailed stormwater drawings…

103. On-site Water Management System Prior to the issue of any Occupation Certificate, the stormwater runoff from the site shall be collected and disposed of to the street drainage system in Eastern Valley Way via a water quality improvement system and an approved OSD system with a minimum volume of 167m3 in accordance with AS/NZS3500.3, Part I of Council’s DCP and Technical Standard 1. The OSD system shall limit the peak stormwater flow from the site in the 1%AEP event to 115L/s. The construction of the stormwater drainage system of the proposed development shall be in accordance with the approved detailed stormwater drawings required under this development consent and Council’s…

105. On-site Water Management System Prior to the issue of any Occupation Certificate, the stormwater runoff from the site shall be collected and disposed of via an approved OSD system with a minimum volume of 156m3 that limits the peak outflow from the site to 152L/s in the 1%AEP event and water quality improvement system. The system will be in accordance with Sydney Water’s requirements AS/NZS3500.3, Part I of Council’s DCP and Technical Standards 1 and 2. The construction of the stormwater drainage system of the proposed development shall be in accordance with the approved detailed stormwater drawings required under this development consent and Council’s specification (AUS-SPEC).…

11. Stormwater to Street Drainage via Reinforced Concrete Pipe (RCP) Stormwater runoff from the site shall be collected and conveyed to the underground drainage system in Walter Street and Willoughby Road via a 375 mm RCP in accordance with Council's specification. A grated drainage pit (min. 600mm x 600mm) shall be provided within the property and adjacent to the boundary prior to discharging to the Council’s drainage system. In this regard, full design and construction details showing the method of disposal of surface and roof water from the site are to be submitted to Council for approval prior to the issue of the Construction Certificate. (Reason: Prevent nuisance flooding)

113. On-site Water Management System Prior to the issue of any Occupation Certificate, the stormwater runoff from the site shall be collected and disposed of to the Council drainage system via a water quality improvement system and an OSD system with a minimum volume of 93m3 in accordance with Sydney Water’s requirements AS/NZS3500.3, Part I of Council’s DCP and Technical Standard 1. The construction of the stormwater drainage system of the proposed development shall be in accordance with the approved detailed stormwater drawings required under this development consent and Council’s specification (AUS-SPEC). (Reason: Prevent nuisance flooding)

23. Analysis of Outlet Condition The capacity of the outlet pipe to the Council system shall be hydraulically evaluated using the Hydraulic Grade Line method to ensure that the outlet from the OSD system is above the downstream water level for the 1%AEP storm event. The adopted downstream water level at the connection to the Council system shall be the top of kerb level. Full engineering details of the hydraulic evaluations prepared and signed by a practising Civil Engineer shall be submitted to the Certifying Authority prior to the issue of the Construction Certificate. (Reason: Prevent property damage)

74. Stormwater Runoff from Upstream Lots Prior to the issue of any Occupation Certificate, if necessary to divert upstream flows around the site, provide an interceptor drainage system to capture and convey all stormwater runoff from the upstream neighbouring property to the Council or public drainage system. The drainage system is to comprise suitable inlet pits, grated drains, pipes and channels and is to be designed in accordance with Part C.5 of the Council’s WDCP. This drainage system is to be designed for storm events up to and including the 1%AEP storm event. (Reason: Prevent nuisance flooding)

14. Overland Flow A suitably qualified and experienced civil engineer must certify that the vehicle access to the basement parking area has been designed to prevent overland stormwater flow from the laneway draining into the basement. The engineer must undertake an assessment of the critical flows as determined necessary to satisfy this condition. Where floor levels need to be raised or other flood protection measures are deemed necessary, details must be submitted and approved by the Certifying Authority prior to the issue of the Construction Certificate. (Reason: Prevent property damage)

14. Overland Flow A suitably qualified and experienced civil engineer must certify that the vehicle access to the basement parking area has been designed to prevent overland stormwater flow from the laneway draining into the basement. The engineer must undertake an assessment of the critical flows as determined necessary to satisfy this condition. Where floor levels need to be raised or other flood protection measures are deemed necessary, details must be submitted and approved by the Certifying Authority prior to the issue of the Construction Certificate. (Reason: Prevent property damage)

35. Flood Affected Development Based on the flood information obtained from Council, a Flood Risk Management Report prepared by a qualified civil engineer experienced in flood analysis and management and complying with the requirements in Part I of the Willoughby DCP and Technical Standard No. 2, “Floodplain Management” and the NSW Government’s Floodplain Development Manual 2005, shall be submitted with the application for Construction Certificate. All measures contained in the report shall form part of any Construction Certificate issued. (Reason: Managing Flood Risk)

109. Stormwater Runoff from Upstream Lots Prior to the issue of any Occupation Certificate, provide an interceptor drainage system to capture and convey all stormwater runoff from the upstream neighbouring property to the Council or public drainage system. The drainage system is to comprise suitable inlet pits, grated drains, pipes and channels and is to be designed in accordance with Part I of the Council’s WDCP and AS/NZS 3500.3. This drainage system is to be designed for storm events up to and including the 1%AEP storm event. (Reason: Prevent nuisance flooding)

127. Overland Flow Path – Engineers Certification Prior to the issue of any Occupation Certificate, submit to Council written certification, prepared by a suitably qualified and experienced civil engineer (generally CPEng), that: (a) The finished floor levels of the proposed dwelling and garage have a minimum freeboard of 500mm and 300mm respectively above the 1% AEP flood event, which is conveyed through the site. (a) The as-constructed works comply with the requirements of Technical Standard 2. (Reason: Ensure compliance)

11. Analysis of Outlet Condition The capacity of the outlet pipe to the Council system shall be hydraulically evaluated using the Hydraulic Grade Line method to ensure that the outlet from the OSD system is above the downstream water level for the 1%AEP storm event. Full engineering details of the hydraulic evaluations prepared and signed by a practising Civil Engineer shall be submitted to the certifying authority for approval prior to the issue of the Construction Certificate. (Reason: Prevent property damage)

28. Analysis of Outlet Condition The capacity of the outlet pipe to the Council system shall be hydraulically evaluated using the Hydraulic Grade Line method to ensure that the outlet from the OSD system is above the downstream water level for the 1%AEP storm event. Full engineering details of the hydraulic evaluations prepared and signed by a practising Civil Engineer shall be submitted to Council for consideration prior to the issue of the Construction Certificate. (Reason: Prevent property damage)

12. Analysis of Outlet Condition A hydraulic grade line analysis shall be undertaken to ensure that the outlet from each OSD tank is above 1%AEP downstream water level. Full engineering details of the hydraulic evaluations prepared and signed by a practising Civil Engineer shall be submitted to the Certifying Authority prior to the issue of the Construction Certificate for each stage. (Reason: Prevent property damage)

128. Overland Flow Path – Work As Executed Plans Upon completion of the development, work-as-executed (WAE) plans, based on the approved plans, shall be prepared by a registered surveyor and submitted to Council. The plans shall show the extent of works and finished ground levels within the overland flow path. Any minor changes or variations to the approved plans shall be highlighted in red. (Reason: Record of works)

16. Flood Level A suitably qualified and experienced civil engineer must certify that the finished floor levels of the proposed development comply with the minimum freeboard requirements of Technical Standard 3 and are in accordance with the recommendations of the Hydrology and Hydraulic Analysis report dated 30 July 2021 prepared by Calibre. (Reason: Prevent property damage)

121. Overland Flow The applicant’s attention is drawn to potential overland flow from the upstream catchment. Appropriate measures where required shall be implemented to ensure overland flow does not enter the building and no additional flow is directed onto adjoining property. (Reason: Protection of building)

147. Analysis of Outlet Condition All storage outlet pipes from the OSD tank shall be above the 1% Annual Exceedance Probability (AEP) event water level. (Reason: Maintain designed discharge)

119. Analysis of Outlet Condition All storage outlet pipes from the OSD tank shall be above the 1% AEP event water level. (Reason: Maintain designed discharge)