B4.A Flood compatibility


    Objectives

  • Development is compatible with the flood hazard category of the land.

  • Development mitigates risks to life and property.

  • Development avoids adverse cumulative impacts that increase risks for surrounding properties.


      Controls

      B4.1 Development is in accordance with Figure 5, having regard for the flood hazard category of the land (see Figure 6).

      Note

      Development deemed unsuitable in accordance with Figure 5 is not supported. 

      B4.2 The proposed development must be located on the land with the lowest flood risk.

      B4.3 Development must meet the minimum finished floor level (FFL) as specified in Figure 8.

      B4.4 The finished surface of open space car parking, carports and driveways should be designed having regard to vehicle stability, including consideration of depths and velocity during inundation by flood waters.

      Note

      The National Construction Code may provide minimum FFLs for some categories of development which prevail to the extent of any inconsistency with these controls.


      Figure 8: Finished floor level (FFL)

      Development type
      Required FFL
      Residential accommodation
      • Habitable rooms – flood planning level
      • Non-habitable rooms – adaptable minimum floor level
      • Flood refuge – probable maximum flood Level 
      Subdivision
      Flood planning level
      Farm buildings (non-habitable/ancillary to agricultural use)
      On-site waste water level
      Commercial and industrial premises
      Garages, open car parking spaces and carports
      Current day 1% AEP flood level
      Driveways and access
      Current day 1% AEP flood level, or the flood immunity
      of the connecting public road


      B4.5 Development for a building (and/or an associated driveway or access) must be of a flood compatible design and construction and shall meet the relevant requirements in the Construction of Buildings in Flood Hazard Areas (Australian Building Codes Board). Council may also require structural certification for development proposed on land which becomes a floodway in the PMF.

      B4.6 Fencing on flood prone land should be stable in events up to the current day 1% AEP flood event and not obstruct the flow of floodwater.

      B4.7 For development proposed on land defined as floodway:

      • Development other than farm buildings and/or fill is not supported on land identified as either low hazard floodway or high hazard floodway; and
      • Fencing in a floodway should not include non-permeable materials or fencing types that could restrict or redirect flood waters.

      B4.8 All incoming main power service equipment, including all metering equipment, and all electrical fixtures, such as power points, light fittings, switches, heating, ventilation and other service facilities must be located above the FPL, or where possible above the PMF.

      Where the above cannot be achieved, the following features shall be used:

      • Electrical cabling is not to be installed within walls, or chased into walls; and
      • Any circuit containing switches, power points or any other electrical fitting that are located below the FPL, shall connect to the power supply through an individual Residual Current Device (RCD), located in the meter box.

      B4.9 The storage of hazardous or potentially hazardous materials, potentially polluting material or material that could be washed from site and cause harm downstream must be stored above the FPL with appropriate mitigation measures, such as bunding.

      B4.10 Items that may wash away during flood events (e.g. rainwater tanks, hot water tanks, gas cylinders, shipping containers) must be elevated above the 1% AEP flood event level in the year 2100 (without freeboard) or anchored (installed) to resist buoyancy and impact forces.

      B4.11 A flood impact and risk assessment is required for development on all flood prone land (other than minimal risk flood prone land) that includes:

      • Any fill on land identified as floodway.
      • Any fill located in a flood storage area, unless:
        • The net volume of fill does not exceed the lesser of 20% or 2000m3 of the flood volume of the lot in the 1% AEP flood event in the year 2100 (this includes consideration of previous fill volumes); and
        • It is demonstrated that the fill does not adversely affect local drainage patterns of all events up to the 1% AEP flood event in the year 2100.

      Note

      Fill in flood storage areas greater than the abovementioned volume can be offset by flood storage. Offsetting can be achieved through consolidation of lots and/or assigning an ‘easement to flood land’ on the compensatory lot/s. Compensatory lots must be located within the zone of influence of the proposed fill (as demonstrated by the flood impact and risk assessment) or adjacent to the proposed fill and be of the same hazard category of the subject site.

      • Any fill for the purposes of a livestock flood refuge mound, unless the livestock flood refuge mound is located in an identified flood fringe area:
        • The volume/size and location of the livestock flood refuge mound meets the criteria in Figure 9; and
        • The size of the mound must have regard to the agricultural capacity of the land. The design and size of the mound shall be determined by reference to the NSW Department of Primary Industries –Agriculture. 2009, ‘Primefacts: Livestock flood refuge mounds’; and

      Note

      ‘NSW Department of Primary Industries – Agriculture 2009, ‘Primefacts: Livestock flood refuge mounds’ provides guidance for flood mound design, however the Primefact guidelines do not override other DCP and LEP flood impact considerations such as adverse impacts to adjoining properties.

      • Where the proposed development could change flood behaviour, affect existing flood risk, or expose people to flood risks that require management; or
      • If Council determines a flood impact and risk assessment is necessary for any other reason.

      Campvale Drain Inundation Area

      The Medowie Floodplain Risk Management Study and Plan 2016 must be referred to for guidance on adding fill in the Campvale Drain Inundation Area.

      Figure 9: Livestock flood refuge mound

      Size of mound
      Distance from nearest property
      20m x 20m (at current day 1% AEP flood level and 0.5m below the current day 1% AEP flood level)
      > 180m
      20m x 20m (1.0m below the current day 1% AEP flood level)
      > 40m
      20m x 20m (1.5m below the current day 1% AEP flood level)
      > 25m
      40m x 40m (at current day 1% AEP flood level, 0.5m below the current day 1% AEP flood level and 1.0m below the current day 1% AEP flood level)
      > 830m
      40m x 40m (1.5m below current day 1% AEP flood level)
      > 170m


      Note

      Interpolation between the values listed above, should be based on the length of the mound perpendicular to the direction of flow, followed by the depth below the current day 1% AEP flood event level.

      NSW’s Flood Risk Management Guideline Lu01 provides flood impact and risk assessment FIRA requirements to support development.

      B4.12 A site based overland flow report must be submitted for development located within a designated overland flow path. The purpose of this report is to demonstrate that the development:

      • Will not result in material increase in flood level or flood hazard upstream, downstream or surrounding properties; and
      • Will provide acceptable management of flood risk with appropriate development levels to ensure the safety of people.

      B4.13 Subdivision that creates the ability to erect additional dwellings is to indicate building envelopes above the FPL and demonstrate how future development can comply with the requirements of B4.B of this chapter.