Flood certificate vs flood model report: what each tells you

A council flood certificate states the council's adopted flood level for a property, usually for one planning event, as a formal document for building and development applications. A flood model report reads the published flood model grids across the property and lists the modelled depth, velocity, depth x velocity and flood level for every event the publisher modelled. The certificate is the document a certifier or council assessor asks for. The model report is a screening read of the published modelling, used earlier, to see whether water reaches the lot at all and in which events.

What is a council flood certificate?

A flood certificate is a council's written statement of the flood information it holds for one lot. The name varies between councils: flood certificate, flood search, flood level information, flood information request or flood advice letter. Some councils publish a free online property flood report instead, such as Brisbane's FloodWise Property Report. Others charge a fee and take several days to issue one, and some do not offer one.

The contents also vary, but a certificate usually gives:

• the defined flood level (DFL) for the lot, in metres AHD, for the council's planning event, most often the 1% AEP (1 in 100 year) flood
• the flood planning level, which is the DFL plus a freeboard margin, and the minimum habitable floor level that follows from it
• the flood study the level comes from
• sometimes ground levels on the lot, or a recorded level from a past flood

The council's adopted level is the number a building or development application is assessed against. That is what the certificate is for.

Is a flood certificate the same as a section 10.7 certificate?

No. In NSW, the section 10.7 planning certificate says whether flood related development controls apply to the land. It does not usually give a flood level, a depth or an extent. Those come from the council's flood study and a flood certificate or flood information request, where the council offers one.

What does a flood model report show?

The LayeredGeo Flood Model Report is built from flood model grids that councils and state agencies have released as open data, and from flood studies licensed to LayeredGeo by councils and state agencies, which are not necessarily available to download. For each published study that reaches the property it lists every modelled event, present day and future climate where the publisher ran both, and for each event gives the surfaces the publisher released:

• modelled depth of water above the ground
• modelled velocity
• depth x velocity, the product used to classify flood hazard
• modelled flood level in metres AHD
• a map of the event over the property

Each study is marked as water on the property, water near the boundary with the distance stated, assessed and dry, or not assessed. The report also has a Recorded Floods page for mapped extents of past floods, and a Sea Level Rise Indication page for coastal addresses near a tide gauge. It is a screening report from published modelling. It is not a site-specific flood study and not a flood certificate.

What is the difference between a flood certificate and a flood model report?

	Flood model report	Council flood certificate	Planning scheme flood overlay
What you get	Modelled depth, velocity, depth x velocity and flood level for every published event, plus a map of each and the recorded flood extents	The council's adopted flood level for the property, as a formal document	A yes or no overlay polygon and the development controls that follow from it
Events covered	Every event the publisher modelled, present day and future climate	Usually the one adopted defined flood level	The single mapped planning event
Cost and wait	$9, minutes, no account	Typically $50 to $60 and several days to a fortnight, where the council offers one	Free, but only where the council maps it
Use it for	Deciding whether to buy, what to ask for and whether a certificate is worth ordering	Lodging a building or development application	Understanding what the council will assess

Why can a flood certificate and a flood model report give different numbers?

The two often start from the same flood study, but they report it differently.

• One level or many. A certificate usually quotes one adopted level. A model report gives a result for each event, so a lot that is dry in the 1% AEP flood may still show water in the 0.2% AEP flood or the probable maximum flood (PMF).
• Freeboard. A flood planning level includes a freeboard margin, often around 0.5 m, above the modelled level. A model report quotes the modelled level without freeboard.
• A point or the whole lot. A certificate may give the level at one point. A model grid read across a property can show a range, because water surfaces slope along a floodplain.
• Which study. A council may have adopted a newer study than the one released as open data, or hold a study that was never released. The certificate reflects the adopted study.

Where the numbers differ, the council's adopted level is the one that controls building. The model report is useful for knowing what to ask the council about.

Which one do I need before buying a house?

For most buyers the order is screening first, certificate second. A model report shows whether any published model puts water on or near the lot, and in which events. If it does, a flood certificate gives the adopted level that a renovation, extension or rebuild would be designed to. If the lot is dry in every modelled event including the rarest, check the council's adopted flood mapping and flood information for the lot before deciding whether a certificate is needed, since the council may rely on a study the report does not hold.

For design and building work, the certificate, the planning scheme and a surveyed floor level are the inputs. A surveyor measures floor and ground levels in metres AHD so they can be compared with the flood level. The QLD flood model report checklist explains each number in more detail.

Does a flood certificate show past floods?

Sometimes. Some councils include a recorded flood level from a past event. Recorded flood extents are published separately by some councils and states, and they are covered in how to find out if a house has flooded before.

Common questions

What is a flood certificate?

A flood certificate is a council document stating the flood information it holds for a lot, usually the defined flood level in metres AHD, the flood planning level and the minimum floor level. It is used for building and development applications, and the name, contents and fee vary between councils.

Is a flood certificate the same as a section 10.7 certificate?

No. A NSW section 10.7 planning certificate says whether flood related development controls apply to the land. It does not usually give a flood level or depth, which come from the council's flood study or a separate flood information request.

Can I use a flood model report for a building application?

No. A building or development application is assessed against the council's adopted flood level, which comes from the council. A flood model report is a screening document for deciding whether to buy and what to ask the council.

Does a flood model report cover every address?

No. It covers an address where a published flood study reaches the property. The free coverage check shows whether that is the case before anything is paid for.

The free coverage check shows whether a published flood model reaches an address before a report is bought. The flood overlay and the other planning controls on the lot are in the Property Report.

LayeredGeo's Flood Model Report collects every published flood model that reaches a property, with modelled depth, velocity and flood level for each event.

About this article. Published by LayeredGeo. It is general information about how property and ground conditions are assessed in Australia, not engineering, planning, legal or financial advice, and it is not specific to any property. Check anything that matters against the source dataset or a suitably qualified professional before you rely on it. If you spot something wrong, tell us at hello@layeredgeo.com.au and we will fix it.

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