Overland flow
Does anyone have more information on the impact of overland flow on subdivision applications?
After some research, I've noticed there are additional requirements to address namely:
http://www.brisbane.qld.gov.au/CP/FloodPSP#RequirementsReconfiguringLot
http://www.brisbane.qld.gov.au/CP/FloodOC#Table82113c
I'm particularly interested in Table 8.2.11.3.J Flood planning levels for reconfiguring a lot, referred to in AO 18.1 below:
Additional criteria for reconfiguring a lot
PO17
Development locates and designs all lots resulting from reconfiguring a lot to:
(a) minimise the risk to people from flood hazard;
(b) minimise damage to property from flood hazard;
(c) facilitate safe and efficient evacuation.
Note?
Consideration of all floods up to the probably maximum flood is relevant to minimising the risk to people.
Flood warning time is not considered sufficient in the Creek/waterway planning area sub-categories or the Overland flow flood planning area sub-category.
Filling above the flood planning level for a flood event greater than the defined flood event cannot be assumed to mitigate the flood hazard.
AO17.1
Development creating new lots is to comply with Table 8.2.11.3.I.
AO17.2
Development provides for reconfiguring a lot design that achieves a road and lot layout which:
(a) provides trafficable vehicular egress for evacuation during a defined flood event;
(b) optimises hazard-free movement away from sources of flood hazard within the development.
Note?Further advice on road and lot layout is contained in the Flood planning scheme policy.
AO17.3
Development which creates a new residential lot in an area subject to Brisbane River flooding, if the residential flood level is greater than 12.8m AHD is not subject to a hydraulic hazard greater than 0.6m2/s DV or 0.6m deep in a 0.2% AEP flood.
Note?Refer to the Flood planning scheme policy for further explanation on the 0.2% AEP flood.
PO18
Development involving reconfiguring a lot:
(a) minimises the risk to people from flood hazard;
(b) creates safe evacuation routes or avoids isolation of the development during a flood greater than the defined flood event;
(c) minimises damage to property and services;
(d) provides lots and roads that are not frequently flooded or subject to nuisance ponding or seepage;
(e) ensures lots created for park or private open space minimise the risk to people from flood hazard and are fit for purpose;
(f) provides a lot that is not substantially burdened by flood mitigation infrastructure.
AO18.1
Development involving reconfiguring a lot ensures:
(a) all lots with the flood planning levels in Table 8.2.11.3.J;
(b) a new road complies with the flood planning levels in Table 8.2.11.3.F.
AO18.2
Development involving reconfiguring a lot creating more than 6 residential lots or a lot for industry ensures the flood planning levels of a dedicated road fronting the development or providing primary access within 200m of the development is:
(a) complies with Table 8.2.11.3.K; or
(b) has acceptable trafficability in accordance with the requirements in the Flood planning scheme policy and the Queensland Urban Drainage Manual.
Note?The Flood planning scheme policy contains supporting information about trafficability on existing roads and serviceability during floods.
AO18.3
Development protects the conveyance of flood hazard area by providing an easement over the:
(a) 2% AEP flood extent for overland flow flooding;
(b) 1% AEP flood extent for creek/waterway flooding.
A flood risk assessment is required for residential reconfiguring a lot development where creating more than two new lots in the overland flow flood planning area sub-category.
Additional requirements apply for the Brisbane River flood planning area sub-category if the residential flood level is greater than 12.8m AHD.
Minimum site levels, requirements for no adverse off site impacts and other provisions in the planning scheme still apply.
From what I'm reading you need to mitigate against floods 2 per cent AEP plus 300mm. How does one mitigate the risk of overland flow at the subdivision stage as opposed to the building stage, especially for flat land.