Flooding and overland stormwater flow impact assessments
Your proposed development must not result in adverse impacts from flooding or overland flow of stormwater. Hydrologic and hydraulic investigations must be carried out to demonstrate that the proposed development will not adversely impact on flooding to upstream, downstream or adjacent properties, or create nuisance ponding on other properties.
Where necessary, suitable impact mitigation measures must be implemented. A Registered Professional Engineer QLD (RPEQ) with the relevant expertise and experience in hydrological and hydraulic assessment needs to undertake the work.
The level of detail required to describe proposed works may vary depending on the level of development approval sought. A RPEQ must scope the requirements. This is to ensure an appropriate assessment of the flooding and overland stormwater flow impacts and proposed works is provided for that particular development.
The following technical guides can assist applicants and consultants in the preparation of these documents:
- Technical expert guide lodgement requirements for a Flood study (Word - 130kb)
- Technical expert guide lodgement requirements for a Site based stormwater management plan (Word - 121kb).
Flood Study - minor hydraulic assessment
Typically, minor hydraulic assessment is required for applications within Brisbane City Council's mapped overland flow paths where the primary concern is related to flood immunity, for catchments <30 ha or where average flow depths are shallow (typically <500 mm). Minor alterations to the floodplain are permissible under a minor assessment at the discretion of Council.
Flood Study - major hydraulic assessment
Typically, major hydraulic assessment is required for larger catchments and creeks. This assessment may also apply to applications in overland flow paths where flood impacts and flood immunity are assessed in regard to:
- the effect of filling or buildings on flooding and overland flow
- effects of structures such as bridges, culverts on hydraulics
- major flow piped solutions (e.g. +20 year average recurrence interval (ARI) pipelines)
- any development within a waterway corridor
- where retention or detention basins and new open channels are proposed.
The following tables outline the general requirements for hydraulic reporting and assessment.
Table 1 - Flood study content
- The flood study must be signed, dated and referenced by a Registered Professional Engineer QLD (RPEQ) who has overseen the modelling for the design of development.
- Existing site survey plan from a a registered surveyor to scale with cadastral boundaries, ground levels, existing structures, trees, fences, kerb and road levels, pipe invert levels and pit surface levels shown.
- Plan and sections of the development proposal clearly showing habitable, non-habitable levels, proposed fill levels and extent and relevant ground levels.
- Catchment plan to scale with hydrological calculations.
- Plan to scale, showing the location of all hydraulic model cross sections.
- Drawing showing the cross sections of any filling or excavation.
- Report describing modelling methodology (including justification of assumptions used and any limitations) and results:
|Minor assessment||Major assessment|
Table 2 - standards for Flood studies
|Assessment of impacts||
|Piping overland flows||Generally piping of all overland flows as a solution is impractical and not permitted, as:
|Building over or near stormwater||
Flood risk assessment
In some cases, when determined by assessment against either the Flood overlay code or the Coastal hazard overlay code, a flood risk assessment may be required. Information to be contained within a flood risk assessment may be found in the Flood planning scheme policy and the Coastal management planning scheme policy.