B3.A Stormwater quantity


    Objectives

  • To minimise impacts on water balance, surface water and groundwater flow and volume regimes and flooding.
  • To ensure development considers and manages stormwater quantity impacts within a site and on the surrounding area.
  • To ensure development takes into account local constraints and manages stormwater to minimise risk and nuisance caused by localised drainage issues.
  • To ensure development provides a legal and physical point of stormwater discharge.
  • To encourage the provision of stormwater detention on a lot and regional scale.
    • To ensure stormwater quantity is managed during construction to avoid environmental impacts.

Note

The controls below set out requirements for development to meet the above objectives. If a development application can meet the objectives by an alternative solution, Council will be flexible in applying these provisions of the DCP (See section 4.15(3A) of the EP&A Act).

Controls

B3.1 General requirements for all development:

  • Development is designed to ensure stormwater is managed and controlled to minimise risk and nuisance to neighbouring properties, public roadways, public spaces, and the environment. 
  • Development ensures stormwater leaves the site via a legal and physical point of discharge.
  • Development is designed to align with Council’s design specification 0074 Stormwater Drainage Design including the Future effective impervious table.
  • Development is designed to align with Council’s Soil Infiltration Technical Information Sheet and Hydrologic Soil Mapping.
  • Development ensures erosion and scour is managed on-site and avoids the discharge of concentrated surface flow during construction.
  • Development for subdivision of more than 5 lots requires the provision of regional stormwater treatment measures and the preparation of a Water Sensitive Urban Design Strategy, unless it can demonstrate access to a regional stormwater treatment system with sufficient stormwater quantity and quality management capacity.
  • Development ensures erosion and scour is managed on-site and avoids the discharge of concentrated surface flow during construction

DASH

The DASH sets out the information that is required to accompany a development application to address the relevant objectives and controls of this chapter.

B3.2 General requirements for all development with onsite infiltration / detention:

  • On-site infiltration / on-site detention design is to be provided by either underground chambers, surface storage or a combination of the two and are generally positioned:
      • under grassed areas for any cellular system (which can be easily maintained).
      • under hardstand areas such as driveways for any concrete tank structures.

B3.3 General requirements for all rear sloping lots:

  • Rear sloping lots that naturally drain away from the road frontage and are not serviced by an existing drainage easement or inter-allotment drainage system must provide a legal point of discharge and apply the following:
      • The provision of a drainage easement may be required through adjoining private land if a legal point of discharge is not available.
      • A charged drainage system to the street may be considered for roof drainage if it is demonstrated to be functional.
      • It must be demonstrated that neighbouring properties are not adversely impacted for all design storm events up to and including the 1% AEP events.

B3.4 General requirements for lots that naturally drain directly to a public reserve or waterbody:

  • If a public drainage connection is not available, on-site detention or infiltration is not required provided the following is achieved:
      • Stormwater discharges up to the 1% AEP event are managed and controlled within the site to avoid offsite scour and erosion.
      • Flows must not cause nuisance to the downstream environment.

B3.5 Additional requirements for development in areas with a regional stormwater treatment system (Water Sensitive Urban Design Strategy or WSUD Strategy):

  • If the total impervious site coverage (both existing and proposed impervious areas) is below the allowance identified in the applicable WSUD Strategy, requirements in clause B3.1 do not apply.
  • If the total impervious surface site coverage exceeds the requirements of the applicable WSUD Strategy, additional treatment is required for the excess impervious area as per the requirements in Figure 3: Stormwater control area requirements.

Note

Some areas have regional stormwater management treatment systems with an accompanying WSUD Strategy including requirements for managing stormwater. To find out if a WSUD Strategy applies go to Council’s website.


B3.6 Additional requirements for development in stormwater control areas:

  • Development is to satisfy the requirements set out in Figure 3: Stormwater control area requirements, below.
  • If on-site infiltration is demonstrated to not be appropriate due to the site conditions the requirements for clay soils apply.
  • Pre-developed flow rates are to be calculated for the day assuming that the site is greenfield and hence 100% pervious.

Note

Stormwater control areas are areas that are zoned for urban development but do not have an approved WSUD strategy and are identified on Council’s mapping.

Figure 3: Stormwater control area requirements

Development Stormwater quantity control area requirements

Sandy Soils

(Types A & B)

Clay Soils

(Types C & D)

Small-scale residential development, including:

  • Alterations and additions
  • Dwelling house
  • Secondary dwellings
  • Attached and semi-detached dwellings
  • Dual occupancies
  • Two-lot subdivision
  •  Ancillary structures

  1. A Deemed to Comply solution can be used
    OR
  2. 2. Provide a stormwater management plan that includes stormwater mitigation (as per the requirements for the development type “All other development”).
All other development

Infiltration requirements

For on-site infiltration:

  • The rainfall depth for the 10% AEP event is to be infiltrated within the site without runoff, and
  • The post-developed peak flow rate is to be less than the pre-developed flow rate for all flood events up to the 1% AEP.
For a regional stormwater quantity management system:

  • The post-developed peak flow rate is to be less than the pre-developed flow rate for all flood events up to the 1% AEP.

Detention requirements

For an on-site and regional stormwater quantity management system:
  • The post-developed peak flow rate is to be less than the pre-developed flow rate for all flood events up to the 1% AEP.