FPL: Flood Planning

What the control sets

Clause 5.21 applies to land the consent authority considers to be within the flood planning area — in practice, land at or below the flood planning level, which some LEPs also show on a Flood Planning Map. On that land, consent must not be granted unless the consent authority is satisfied the development:

• —is compatible with the flood function and behaviour on the land;
• —will not adversely affect flood behaviour in a way that results in detrimental increases in flood impacts on other development or properties;
• —will not adversely affect the safe occupation and efficient evacuation of people, or exceed the capacity of existing evacuation routes, in the event of a flood;
• —incorporates appropriate measures to manage risk to life in the event of a flood; and
• —will not adversely affect the environment or cause avoidable erosion, siltation, destruction of riparian vegetation or a reduction in the stability of river banks or watercourses.

The clause also requires regard to be had to the government’s flood risk management guidance. Nothing in it sets a floor level, a fill limit or a maximum footprint — those come from the council’s development control plan and from the flood study behind the mapping, which is why a scheme can satisfy the clause on one site and fail on another with the same mapped affectation.

The flood planning level, and where the number lives

The flood planning level has traditionally been the level of a 1% annual exceedance probability flood event — the one-in-a-hundred-year flood — plus 0.5 metres of freeboard, and the Standard Instrument definition now points to the NSW flood risk management guidance, so the exact basis is worth confirming with the council. The definition is in the instrument. The level is not.

Freeboard is not a rounding allowance. Half a metre added to the modelled flood level is half a metre of ground floor that has to be raised, and on a site where the street is at or near the flood level it converts directly into ramp length, a raised entry, and a frontage that no longer meets the footpath cleanly.

Land above the flood planning level is not automatically clear

A companion clause — clause 5.22, special flood considerations — reaches land between the flood planning level and the level of the probable maximum flood, and applies to particular kinds of development where the consequences of being caught are severe: sensitive and hazardous uses, and development involving the vulnerable or those who cannot evacuate unaided.

So a seniors housing or childcare proposal on land above the flood planning level can still be assessed for flood, on evacuation grounds, when a townhouse project on the same land would not be. Whether a council has adopted clause 5.22 is LEP-specific.

What flood affectation actually costs a development

Four things, in rough order of how often they decide a scheme.

Ground floor level. Habitable floors go at or above the flood planning level. On an affected site that is fill, a suspended slab, or both — and it eats headroom against the mapped building height, because the height is measured from existing ground level, not from your new one.

Basement parking. Entries need their own protection above the flood planning level, and some councils will not accept basement parking on high-hazard land at all. Losing the basement on a site whose yield assumed it usually ends the scheme rather than trimming it.

Flood behaviour. Filling a site displaces water somewhere else, and the second bullet of the clause is about exactly that. A compensatory-works or no-net-loss requirement turns fill from a cost into a design constraint.

Evacuation. The hardest one to fix late, because it is a property of the surrounding road network rather than of your site. Where an area has a known evacuation constraint, additional population is the thing being resisted, and no amount of on-site design answers it.

Sources

• Standard Instrument — Principal Local Environmental Plan, clause 5.21 Flood planning and clause 5.22 Special flood considerations
• Standard Instrument Dictionary — “flood planning level”, “flood planning area” and “probable maximum flood”
• The applicable council flood study and development control plan — the source of the flood planning level in metres AHD for a particular property

Related: bush fire prone land is the other hazard control that can change the shape of an application, and it works quite differently — it is not in the LEP at all.