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Definition Major Culvert

  • 1.  Definition Major Culvert

    Posted 18 July 2018 21:32
    Hi All,

    I'm trying to provide clarification and definition for what we should consider a Major Culvert to be. I have looked at various definitions including LGAM Knowledge Base, and the definition provided in grants commission for both Queensland and Victoria. These are not consistent and there does not appear to be a similar type of definition for NSW.

    The way I look at it if I define a major culvert as a culvert from inlet to outlet with a span of >6m most culverts on two lane roads would be considered a major culvert even if they are only Ø375. If I consider a major culvert to be those which are >6m along the centreline of the road single or even double cell Ø1800 culverts would be considered minor.

    From what I have already established there is generally an inspection frequency set for assets which are considered major culverts whereas most Councils appear to only inspect minor culverts on a as required basis. Therefore the definition of what is major or minor carries with it a fair amount of risk to Council regarding inspections and condition monitoring.

    I would love to know if there is an industry standard for this definition, and what other Councils are doing to define this and once defined what inspection frequency has been established.


    Charlette Newall
    Acting Asset Engineer
    Cessnock City Council
    Pro Cert 2

  • 2.  RE: Definition Major Culvert

    Posted 19 July 2018 01:17

    Hi Charlotte,

    I suspect that both Grants Commissions are/were trying to say something along the lines of "water course crossings with a span of greater than 6m along the centreline of the intersecting road carriageway should be counted as bridges for the purposes of grants commission reporting, irrespective of whether they are true bridges or multiple culverts laid side by side", and that they coined the term "major culvert" to act as a short hand description of these multiple culverts.

    As you say there is a big difference between a single 300mm culvert under a road and three 1800mm culverts laid side by side, but the Grants Commissions role is to develop funding formulas so they were probably thinking about the cost of water course crossings, not safety and inspection regimes when they adopted the 6m span to define what should and should not be reported on.

    Having said all that, the really interesting part of your question for me is, how often terms get used without being properly defined, and how much confusion could be avoided if more terms had proper definitions that everyone across all jurisdictions could agree on and use.

    The question I guess becomes who should be responsible for getting terms properly defined and where they should be documented.

    You mentioned the LGAM Knowledge Base and I do my best to document every definition I can find there, but what would be ideal is an "All Levels of Government Wiki" where definitions could be thrashed out and agreed on over time .  I believe it would make everyone's lives much easier.



    Wayne Eddy
    Strategic Asset Planning Coordinator
    City of Whittlesea

    Pro Cert 2

  • 3.  RE: Definition Major Culvert

    Posted 19 July 2018 20:08
    Hi Wayne

    There may need to be a consideration for culverts that do not reach the
    usual major culvert definition but require major costs and / or disruption
    of major traffic routes for repair.

    I recall one 900mm pipe that cost well in excess of 500,000 to replace and
    re-build the road with long detours for heavy traffic while works were

    Rod Bray

    On Thu, 19 Jul 2018 15:16:49 +1000, Wayne Eddy via Institute of Public

    Pro Cert 2

  • 4.  RE: Definition Major Culvert

    Posted 19 July 2018 21:33

    The definition from Ausroads Data Standard for Road Management and Investment in Australia and New Zealand: Version 2 Section 8.3.3 is  "A structure designed to provide passage for road users over an obstacle by spanning it. Major culverts have a cross sectional area of more than 3.4 sq.m."

    Therefore a single 1800mm pipe is considered a Minor Culvert but twin 1800mm pipes is a Major Culvert.

    Daniel O'Hara
    Asset Engineer
    Moreton Bay Regional Council
    Pro Cert 2

  • 5.  RE: Definition Major Culvert

    Posted 23 July 2018 00:22
    Thanks for the heads up about the 'Data Standard for Road Management and Investment in Australia and New Zealand' definition, Daniel.

    Seems to me that its the Australia wide definition that everyone has been hanging out for in recent times.  A big thumbs up to Austroads for putting the standard together and making it freely available to all.  It should help dispel a lot of the confusion around a number of definitions.



    Wayne Eddy
    Strategic Asset Planning Coordinator
    City of Whittlesea

    Pro Cert 2

  • 6.  RE: Definition Major Culvert

    Posted 19 July 2018 21:33
    Hi Charlotte

    An Interesting question with no easy answer.  Common language and definitions are an ongoing problem with multiple groups (Austroads, IPWEA, Grants Commissions, etc) having their own ideas.

    As Wayne says, the various State Grants Commissions individually identify infrastructure based on relatively arbitrary criteria in order to develop funding models.  e.g. "any span over 6 m with a clear flow area not less than 6 sq m is a bridge"  (A 5.9m timber truss spanning a major water course and providing the only crossing for miles is not a bridge?)

    Those standards tend to confine our financial and asset reporting systems because we need to be able to produce reports on that basis.  Those definitions also tend to creep into our language and shutter thinking.

    However when you think about it our maintenance and inspection regimes don't really care about asset dimensions!  What they care about are risk, performance and cost (and increasingly criticality and resilience).  A high risk asset gets priority.  What is the risk if the culvert is blocked?  What is the increased risk of asset failure with lack of maintenance?.  Which assets fail to perform without regular maintenance? Do I get better value from annual cleaning or responding to blockage? etc

    I have seen some drainage asset owners adopt an approach of identifying their inspection and maintenance regimes on the basis of risk - primarily risk of culvert blockage and flooding and risk of asset failure through lack of maintenance.

    My suggestion would be you do the same and then define an inspection and maintenance regime to suit.  It doesn't have to be complicated.  Your Operations team probably already knows what is high, medium and low risk already.


    Graham Lantzke
    Principal Asset Engineer
    WSP Pty Ltd

    Pro Cert 2

  • 7.  RE: Definition Major Culvert

    Posted 19 July 2018 21:33

    Hi Charlette and Mates,

    From my experience, most (if not all) State road authorities in Australia define Major Culverts as structures that have a span, height or diameter greater than 1.8 metres and a waterway area per single cell in excess of three (3) square metres, Austroads suggests 3.4 square metres.

    I'm presuming this position has been adopted so that culverts of this size or greater are large enough to:

    • Walk through (therefore ease of inspection)
    • Warrant significant expenditure (comparatively) should they fail.

    Any single cell culvert greater than six (6) metres along the centre line of the crossing would typically be classed as a bridge.

    Not sure how the Grants Commission would view this approach in light of the "…greater than six (6) metres in length (measured along the centre line of the carriageway)" requirement that local government has to interpret.

    Hope this helps.

    Stephen Verity
    NAMS Council Support | IPWEA Australasia

    Pro Cert 2

  • 8.  RE: Definition Major Culvert

    Posted 19 July 2018 23:43
    ​CHarlette, You could refer to teh QTMR Brideg Inspection manual Regards Greg
    Pro Cert 2

  • 9.  RE: Definition Major Culvert

    Posted 20 July 2018 01:43
    ​Hi Charlette

    Main Roads in Queensland has a Structures Inspection Manual which defines a major culvert.  I would assume that if it doesn't meet the major culvert criteria then it's a minor culvert.  It is available on their website at:

    If you look in Part 1 - Clause 3 you'll find:

    'major' culverts. i.e. meeting the following criteria:
    − metal culverts (steel and aluminium):
    at least one barrel (cell) with span, height or diameter ≥1.2 m, or

    −all other culverts:
    pipes with at least one barrel (cell) with diameter ≥1.8 m, or

    rectangular/oval/arch culverts at least one barrel (cell) with span > 1.8 and height > 1.5 m.

    stock and pedestrian underpasses

    These culverts typically have an opening large enough to:

    • access without specialist equipment and are therefore capable of being inspected relatively easily.

    • close the road and create a significant safety hazard in the event of structural failure.

    I hope this helps

    Kevin Chambers

    OneEng Consulting (Qld)
    Pro Cert 2

  • 10.  RE: Definition Major Culvert

    Posted 20 July 2018 04:26
    Hi all
    interesting discussion which highlights the fact that despite the clearly evolving maturity of asset management in Local Government, there are still "basics" which remain to be addressed.
    The fact that there are significant discrepancies between Local Government entities, State road authorities, Ausroads, Grants Commission and Wiki demonstrates a frustrating lack of national coordination and maturity.

    Having recently undertaken a review of stormwater asset data in South Australia, these inconsistencies were evident at all levels of the asset management process, from data recording and componentisation, to categorising, and financial reporting.   The fact that we still cannot consistently define a "major culvert" says a lot about how much we still dont do well.

    Surely after so many years of statutory obligations on asset reporting, and mature AM training programs from IPWEA and others we should have these basics sorted!

    It seems like a perfect opportunity for an industry wide working group to pull together some fundamental basics , which can be readily adopted across the industry.  I think i can recall Ausroads attempting this when they developed their dictionary of terms, but clearly, we were all too busy to take this seriously enough and commit the time to do it properly once, and now we pay the price with ongoing confusion.

    As for a definition - no I dont have an answer either, but agree with several replies in that the definition should reflect the level of risk associated with the asset-  financial risk of failure or blockage, risk of component failure, realistic useful life, and place in network.  This would only require two  or three relatively simple criteria to be assessed/met, so surely, not too hard to define, and then, problem solved for one and all.....

    Andrew Thomas

    Pro Cert 2

  • 11.  RE: Definition Major Culvert

    Posted 22 July 2018 19:35
      |   view attached
    Hi guys,

    This is the exact same issue I came across 12 months ago. I read all the documentation and rang around all different councils to try and find a common solution. I found that every council was calling a Major Culvert differently.
    Therefore I came up with my own statement which outlined what our council determines a Major Culvert to be.

    Statement is as follows:

    Major Culvert = Any Culvert that has a barrel(s) entry area greater than 1.77m2

    The beauty about this statement for us is that it doesn't matter if it has circular pipes, square or rectangle culverts or a mixture of all. Just calculate the area openings of all barrels and its either a yes or no. This means a singular circular barrel of 1.5m2 in our shire is considered a major culvert.
    This statement was based on many fractures, one of them being risk of collapse, hydraulic performance, resourcing for inspections and our own experience of our assets in our shire.

    I hope this helps you out. So far it has worked out really well for us.
    Please find simple calculator I made attached.


    Pro Cert 2

  • 12.  RE: Definition Major Culvert

    Posted 23 July 2018 21:47

    Hi Charlette,


    The definition appears to vary depending on context, which is hardly surprising in a local government setting.


    Fraser Coast was audited by the Queensland Grants Commission in 2017, specifically including the major/minor culverts and the definition of that. Previously we worked on the general assumption of the 6m of road length as measured in the waterway, i.e if the maximum width of water flowing under the road was 6m or greater it was a major culvert.


    For your information, below is the definition as returned to Fraser Coast from the Qld Grants Commission. Our data is now structured to this definition to support generating data for the yearly return.



    The key is the last part of the definition we provide in the data collection:


    "... Number of major culverts which council has responsibility for, of six (6) metres and over in length, measured along the centre line of the carriageway, from the interfaces where the road approach meets the culvert."


    So I've always taken that to mean the length of road that covers the whole structure – i.e. I wouldn't object if they counted the wingwalls on the end of the structure as well.



    End Quote


    In the image above, the red line is the 6m length we originally built our data on. The blue line is the 6m dimension we were shown by the auditor to use for the Grants Commission. There are some situations in our network where the headwall distance as shown is quite long, say 20-30m, but only has a couple smallish pipes along it's whole length which wouldn't have flagged for us before.



    While this is great for the Qld Grants Commission clarity, it doesn't help me as neatly with doing inspections. Our culvert network is poorly inspected and we have been pushing the level 1 and 2 bridge inspections to also include major culverts in the yearly routine. However, I also took the point of view that major culverts formed of a mass of 375RCPs to be a lower risk asset. At this point in time my yearly major culvert inspections cover all boxes or pipes with a height of 900mm or higher which I take to be a reasonable base level of risk, until each culvert set is assessed for risk in its locality context. I seem to recall when I checked the Qld MRD guide it was a much bigger pipe size before they did inspections, I can't remember if it was 1200, 1500 or 1800, but I took 900 to be enough of a risk as a starting point, considering that they have never been routinely inspected at all in our network.


    While so far I'm focused on major culvert inspections, I believe once we move to minor culverts we'll have to also routinely inspect smaller culverts which may be formed of say a single 3x3 RCBC. How small that single culvert is before it comes down to longer inspection processes (3-5 years instead of yearly), I've not really thought too much about, as inspecting lone 900RCPs across the network is pretty onerous.


    Mark McManus

    Asset Management Officer

    Asset Management/Infrastructure & Environment Service

    T (07) 4125 9736  | E


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    Pro Cert 2

  • 13.  RE: Definition Major Culvert

    Posted 24 July 2018 01:05

    Hi All

    Interesting discussion about the definition of a major culvert vs bridge. This may provide some background. The definitions on bridge and culverts were I believe based on traffic loading standards and not waterway capacity.

    Firstly, in relation to the Grants Commission definition of 6 metres span for a bridge. Most State Road Authorities had standard drawings for timber bridges and for example the Country Roads Board in Victoria entry standard for a 12-foot-wide bridge to take Class 'A' loading was 16-inch stringers spanning 21 feet. Anything shorter than this was classified as a culvert. The Grants Commission collects data on this to monitor the number of timber bridges and there 6 metres correlates with the old standards for timber bridge construction. My understanding is that the number they collect has no bearing on the actual grant commission formula, however it does assist the National understanding of this deteriorating asset class.

    In relation to culverts there is an established Australian Standard AS1597 which is utilised by the precast industry to manufacture "Small Box Culverts" up to 1200mm x 1200mm. Water cross section of 1.44 m2. This equates to a 1350mmm Nominal diameter pipe. For larger span box culverts the State Road Authorities prescribed the design to manufacture utilising traditional reinforced concrete design methods.

    The distinction between small and large was largely determined by factory load testing facilities. The smaller culverts were manufactured to performance standards whereas as larger units were to prescription standards.

    From an Asset Managers perspective Box Culverts should follow the definition of the Australian Standard as the smaller units were for many years constructed to different standards to those 1500mm span and greater and may have different useful lives.

    For simplicity I would classify pipes to 1350mm as small and pipes 1500mm and larger as major. There maybe someone out there with a 1425mm pipe (yes - they did make them). Then make your call although a waterway area of greater than 1.5 m2 would classify them as major.

    I hope this helps clarify your thoughts.

    Murray Erbs
    IPWEA NAMS Chair
    +61 408 941 518

    Pro Cert 2

  • 14.  RE: Definition Major Culvert

    Posted 13 August 2018 22:19
    Thank you everyone who has taken the time to respond. It's reassuring to know I am not the only one having issues with this subject.

    Firstly, I had not considered having separate definitions for financial reporting and inspection / maintenance / asset management processes.

    I have read all the comments and looked at the reference documents which have kindly been provided. I looked at the Austroads Data Standard for Road Management and Investment in Australia and New Zealand: Version 2. However, I feel like a cross sectional area of 3.4m² is too large for the definition of major culvert, based on our Councils and my own appetite for risk. The financial and safety risk of single Ø1800 culvert failing in my opinion is significant. If how I define the asset being major or minor has implications of the frequency of inspections (as it should) then this could have major implications.

    My plan of action following on from this is to get a small group of people together here at Council who will be directly affected by the definition and discuss the information provided here and determine Councils agreed position. That way the people directly affected by the definition are consulted and the decisions for the whole of Council is not subject to only my personal risk appetite.

    Thank you all again - once defined I will provide an update of our decision for those who are interested.


    Charlette Newall
    Acting Asset Engineer
    Cessnock City Council

    Pro Cert 2