Buying in the Hawkesbury floodplain: flood levels and 10.7 flags

Buying land on the Hawkesbury-Nepean floodplain means buying into three sets of rules: clause 5.21 of Hawkesbury Local Environmental Plan 2012, which prevents consent in the flood planning area unless the development is compatible with flood behaviour and can be safely evacuated; clauses 4.2A and 4.2B, which tie dwelling rights and rural subdivision to land above the 1:100 ARI flood level; and Hawkesbury City Council’s Flood Policy 2020, which sets the development controls by hazard category for land affected by the 1:100 ARI event. The section 10.7 planning certificate is where the flags appear, and a flood advice certificate from council gives the adopted 1:100 ARI level for the specific lot. From Windsor, Richmond and Pitt Town through Wilberforce, Freemans Reach, Cornwallis and the Richmond Lowlands, the flood planning level and the evacuation route decide what a house DA must show and, in some locations, whether a house can be approved at all.

Who this is for: buyers considering a house block, rural lot or lifestyle property in the Hawkesbury floodplain who want to know what the planning certificate flags mean, what the flood planning level does to a future house and which LEP clauses can stop a dwelling outright.

What does the 10.7 certificate tell a Hawkesbury buyer?

Section 10.7 of the Environmental Planning and Assessment Act 1979 allows anyone to apply to council for a planning certificate for a parcel of land. A section 10.7(2) certificate contains the prescribed matters under Schedule 2 of the Environmental Planning and Assessment Regulation 2021, including the zone, the permitted uses, the applicable instruments and whether the land is affected by flood related development controls, bush fire, road widening and other hazards; a section 10.7(2) and (5) certificate adds further information council holds, such as recent consents. Hawkesbury City Council’s certificate page describes both types and explains that the certificate must be attached to a contract for sale.

For flood purposes the certificate answers a yes or no question: do flood related development controls apply to the land. The Considering Flooding in Land Use Planning Guideline directs councils to record this under Part 2 or Part 5 of the Schedule 2 certificate matters, and to give an “unknown” answer where the information is not held. What the certificate does not tell you is the flood level, the depth over the lot or the hazard category. For that, Hawkesbury offers a flood advice certificate: the basic version provides the adopted 1:100 ARI flood level and estimated land levels, and the detailed version adds flood event levels, likely velocity, hazard category and hydraulic classification. Order the detailed version for any block where the difference between fringe and floodway is the difference between a house and a paddock.

The common buyer mistake is to stop at the 10.7. A yes on flood controls covers everything from a low-lying corner of a Pitt Town lot to a Cornwallis paddock that goes under in a modest flood; the flood advice certificate and the hazard category are what change the price.

What does clause 5.21 of Hawkesbury LEP 2012 require?

Clause 5.21 (flood planning) applies to land council considers to be within the flood planning area. Subclause (2) states that development consent must not be granted unless council 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 affectation of other properties, will not adversely affect safe occupation and efficient evacuation or exceed the capacity of existing evacuation routes for the surrounding area, incorporates appropriate measures to manage risk to life, and will not adversely affect the environment or cause avoidable erosion or bank instability. Subclause (3) requires council to consider projected climate change effects, the design and scale of buildings, measures to minimise risk to life and ensure safe evacuation, and the potential to modify, relocate or remove buildings.

The evacuation limb is the one that bites hardest in the Hawkesbury. The valley’s flood behaviour, with deep and long-duration flooding behind the Sackville gorge, means evacuation capacity on the regional road network is a real constraint on additional dwellings in the lower parts of the floodplain. A house DA in the flood planning area therefore has to show more than a raised floor; it has to show a credible evacuation route to flood-free land within the available warning time, and council will assess cumulative effects on the route.

Council’s Flood Policy 2020 page explains that the policy sets the information and development controls used to assess DAs for land affected by the 1:100 ARI event, that its Schedule of Flood Related Development Controls is organised by the hazard category in which the development sits, and that it distinguishes new development from additions, alterations, intensification, rebuilding or redevelopment of an existing use, including whether an existing use is in a compatible or incompatible hazard category. The page refers to the policy supporting the former clause 6.3 of the LEP; the flood clause is now clause 5.21 following the State-wide 2021 amendment, and the policy should be read with it.

Which clauses can stop a dwelling outright?

Two rural clauses are unique to the Hawkesbury and catch buyers of acreage. Clause 4.2A (residential development and subdivision prohibited on certain land) applies to RU1, RU2, RU4, RU5, R5, C3 and C4 land. Subclause (3) prohibits a dwelling house on a lot resulting from a road closure, and subclause (5) prohibits a dwelling house on a lot that is below the level of a 1:100 ARI flood event and resulted from a subdivision for the purpose of agriculture approved before 27 June 2003. A great deal of the Richmond Lowlands, Cornwallis and Freemans Reach river flat was subdivided for agriculture under earlier instruments; a lot with that history and no flood-free area cannot carry a house, whatever its size.

Clause 4.2B (additional requirements for subdivisions in certain flood planning areas) applies to subdivisions in RU1, RU2, RU4, R5 and C4 that create a lot other than for a public purpose. Subclause (2) states that consent must not be granted unless council is satisfied there is an area of land on the lot that is above flood planning level and sufficient for the erection of a dwelling house, and subclause (3) defines above flood planning level for that purpose as above the 1:100 ARI flood event level, whether as a natural surface or a level achieved by filling under a previous consent. This is why rural-residential subdivision potential on the floodplain depends on the detailed flood advice: a lot without a 1:100 ARI-free building area cannot be created.

Clause 4.1(1)(b) reinforces the same idea for all subdivision, listing among the objectives that each lot contain a suitable area for a dwelling, an asset protection zone for bushfire and an on-site effluent area where sewer is not available. Clause 6.7 (essential services) adds that consent must not be granted unless water, electricity, sewage disposal, stormwater and suitable road access are available or arranged.

What must a house DA on the Hawkesbury floodplain show?

A DA for a new house, or for rebuilding or substantially extending one, inside the flood planning area needs to satisfy clause 5.21, the Flood Policy 2020 schedule for its hazard category and the general controls of Hawkesbury Development Control Plan 2023, which commenced on 24 July 2023 and whose Part B site analysis requirements expressly call for inherent hazards such as flooding to be identified on the site analysis plan. Hawkesbury DCP 2002 continues to apply to matters not covered by DCP 2023.

Complying development is a further casualty. The Housing Code cannot be used on a flood control lot unless council or a hydraulic engineer certifies the building area is outside the floodway, storage and high hazard areas, so most floodplain houses go through a DA. Buyers should also note that section 164(1)(e)(iii) of the Housing SEPP excludes the City of Hawkesbury from Chapter 6 low and mid rise housing, and section 164(1)(f) separately excludes land within the probable maximum flood extent of the Hawkesbury-Nepean flood study; the density uplift that applies near stations elsewhere in Sydney does not apply here.

A due diligence sequence for a floodplain purchase

1. Obtain the section 10.7(2) and (5) certificate and read the flood related development controls, bush fire prone land and any clause 4.2A road closure or agricultural subdivision notations.
2. Order council’s detailed flood advice certificate for the lot: 1:100 ARI level, estimated land levels, velocity, hazard category and hydraulic classification (floodway, flood storage or flood fringe).
3. Obtain a survey with levels in AHD if the margin between the land and the flood planning level is small; a 300 millimetre difference decides whether a slab or a suspended floor is needed.
4. Check the lot history against clauses 4.2A and 4.2B: how and when the lot was created, and whether a 1:100 ARI-free building area exists on the lot.
5. Map the evacuation route from the lot to flood-free land and consider whether council has previously accepted new dwellings in that location.
6. Check the other overlays that stack on the river terraces: bush fire prone land, acid sulfate soils under clause 6.1, terrestrial biodiversity under clause 6.4 and heritage in Windsor, Richmond and Pitt Town.
7. Price the land on the basis of what can be approved: a raised house on a fringe lot is a different asset from a lot in a floodway with an existing use and no rebuild rights.

Definitions

1:100 ARI flood

The flood with an average recurrence interval of 100 years, equivalent to the 1 per cent annual exceedance probability event; Hawkesbury LEP 2012 clauses 4.2A and 4.2B use it as the dwelling and subdivision threshold.

Flood planning level

The flood level adopted for a planning control, generally the defined flood event plus a freeboard; for clause 4.2B the LEP defines it as the 1:100 ARI level.

Flood planning area

The land below the flood planning level to which clause 5.21 applies, defined by reference to the Flood Risk Management Manual.

Hazard category

The classification of flood hazard on a lot (from low to high, and floodway, storage or fringe) used by the Flood Policy 2020 schedule to set controls.

Flood advice certificate

A Hawkesbury City Council document giving the adopted 1:100 ARI level and land levels for a lot (basic) or adding velocity, hazard and hydraulic category (detailed).

Section 10.7 certificate

The planning certificate issued under section 10.7 of the EP&A Act; the (2) certificate covers prescribed matters and the (5) certificate adds other information council holds.

URBA prepares development due diligence reports for buyers in the Hawkesbury, reading the 10.7 certificate, the flood advice certificate and clauses 4.2A, 4.2B and 5.21 together to say what a lot can carry before contracts are exchanged, and then prepares the Statement of Environmental Effects for the house DA. See our development due diligence report service and our Hawkesbury town planning page, or request a fee proposal for a specific property.