Hi there,
We are about to embark on our KDR project and at an early stage of the tender process our builder has alerted us to fact that we will need a flood report to be done as the council 10.7 report has the following:
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Flood Information The land the subject of this certificate is contained within an area shown grey/grey hatched on plan number XXXXXB being known drainage problem areas. Areas coloured grey/grey hatched on plan number XXXXXB being known drainage problem areas only be permitted to be developed subject to detailed hydraulic investigation of the potential impact of the development in the area.
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I have hidden the plan number (XXXXXB) above assuming it might be specific to our property.
We have been advised that we have to go down the DA route and can no longer do CDC. Could we please check if others have had similar experiences and if there were any recommendations on our options?
Also - if we can get recommendations on a reasonable hydraulic engineer to do this work in Western Sydney?
We have lived in this area for about 20 years and don't see any of the new builds needing elevated heights due to flood concerns.
many thanks in advance.
KDR - hydraulic investigation/flood report
Page 1 of 1
Your builder is likely correct... Part 3, Division 2, clause 3.5 of the complying development code disqualifies development under CDC for flood control lots... refer https://www.legislation.nsw.gov.au/view ... 72#sec.3.5 so that only leaves the option of a DA.
We ran into a similar issue in that even though we're 32m above sea level there is an overland flow path that clips the front corner of the block. Whilst it was unexpected, frustrating and a little worrying at the time, in the end the main effects were:
1. time delay whilst the house design was altered to suit council's development control plan (which was quite different to CDC)
2. time delay & extra cost for the hydraulic engineer to prepare a flood risk management report
3. time delay for DA approval (5 months for DA vs 2 weeks for CDC)
4. extra cost for raising the slab/finished floor level by 540mm (extra fill, piering and drop edge beams)
For us, I contacted the builders hydraulic engineer (the one who would normally do the storm water system design for the builder) and asked his advice which was...
Go to council and ask for information. They quite likely have done a flood study for the area (otherwise how do they know the area is prone to flooding).
Best case scenario is that council give you the flood levels otherwise they will say what information they have.
Whatever they have, get a copy and forward it to the hydraulic engineer which will help him greatly to do a flood risk management report.
A flood study is a time consuming and expensive exercise so if you can get it from council it is a big benefit for you (both time & $$$).
In my opinion you're best to work with the builders hydraulic engineer for this. The storm water design and the flood risk management report are inter related, you'll be duplicating work if you engage a separate engineer.
The builder may prefer that you sign the contract and sort this out by variation later. I wouldn't (and didn't) do that, we insisted this be sorted out at pre-contract administration stage so we knew what the extra costs would be before we were committed to the contract.
We ran into a similar issue in that even though we're 32m above sea level there is an overland flow path that clips the front corner of the block. Whilst it was unexpected, frustrating and a little worrying at the time, in the end the main effects were:
1. time delay whilst the house design was altered to suit council's development control plan (which was quite different to CDC)
2. time delay & extra cost for the hydraulic engineer to prepare a flood risk management report
3. time delay for DA approval (5 months for DA vs 2 weeks for CDC)
4. extra cost for raising the slab/finished floor level by 540mm (extra fill, piering and drop edge beams)
For us, I contacted the builders hydraulic engineer (the one who would normally do the storm water system design for the builder) and asked his advice which was...
Go to council and ask for information. They quite likely have done a flood study for the area (otherwise how do they know the area is prone to flooding).
Best case scenario is that council give you the flood levels otherwise they will say what information they have.
Whatever they have, get a copy and forward it to the hydraulic engineer which will help him greatly to do a flood risk management report.
A flood study is a time consuming and expensive exercise so if you can get it from council it is a big benefit for you (both time & $$$).
In my opinion you're best to work with the builders hydraulic engineer for this. The storm water design and the flood risk management report are inter related, you'll be duplicating work if you engage a separate engineer.
The builder may prefer that you sign the contract and sort this out by variation later. I wouldn't (and didn't) do that, we insisted this be sorted out at pre-contract administration stage so we knew what the extra costs would be before we were committed to the contract.
Your builder is likely correct... Part 3, Division 2, clause 3.5 of the complying development code disqualifies development under CDC for flood control lots... refer https://www.legislation.nsw.gov.au/view ... 72#sec.3.5 so that only leaves the option of a DA.
We ran into a similar issue in that even though we're 32m above sea level there is an overland flow path that clips the front corner of the block. Whilst it was unexpected, frustrating and a little worrying at the time, in the end the main effects were:
1. time delay whilst the house design was altered to suit council's development control plan (which was quite different to CDC)
2. time delay & extra cost for the hydraulic engineer to prepare a flood risk management report
3. time delay for DA approval (5 months for DA vs 2 weeks for CDC)
4. extra cost for raising the slab/finished floor level by 540mm (extra fill, piering and drop edge beams)
For us, I contacted the builders hydraulic engineer (the one who would normally do the storm water system design for the builder) and asked his advice which was...
Go to council and ask for information. They quite likely have done a flood study for the area (otherwise how do they know the area is prone to flooding).
Best case scenario is that council give you the flood levels otherwise they will say what information they have.
Whatever they have, get a copy and forward it to the hydraulic engineer which will help him greatly to do a flood risk management report.
A flood study is a time consuming and expensive exercise so if you can get it from council it is a big benefit for you (both time & $$$).
In my opinion you're best to work with the builders hydraulic engineer for this. The storm water design and the flood risk management report are inter related, you'll be duplicating work if you engage a separate engineer.
The builder may prefer that you sign the contract and sort this out by variation later. I wouldn't (and didn't) do that, we insisted this be sorted out at pre-contract administration stage so we knew what the extra costs would be before we were committed to the contract.
We ran into a similar issue in that even though we're 32m above sea level there is an overland flow path that clips the front corner of the block. Whilst it was unexpected, frustrating and a little worrying at the time, in the end the main effects were:
1. time delay whilst the house design was altered to suit council's development control plan (which was quite different to CDC)
2. time delay & extra cost for the hydraulic engineer to prepare a flood risk management report
3. time delay for DA approval (5 months for DA vs 2 weeks for CDC)
4. extra cost for raising the slab/finished floor level by 540mm (extra fill, piering and drop edge beams)
For us, I contacted the builders hydraulic engineer (the one who would normally do the storm water system design for the builder) and asked his advice which was...
Go to council and ask for information. They quite likely have done a flood study for the area (otherwise how do they know the area is prone to flooding).
Best case scenario is that council give you the flood levels otherwise they will say what information they have.
Whatever they have, get a copy and forward it to the hydraulic engineer which will help him greatly to do a flood risk management report.
A flood study is a time consuming and expensive exercise so if you can get it from council it is a big benefit for you (both time & $$$).
In my opinion you're best to work with the builders hydraulic engineer for this. The storm water design and the flood risk management report are inter related, you'll be duplicating work if you engage a separate engineer.
The builder may prefer that you sign the contract and sort this out by variation later. I wouldn't (and didn't) do that, we insisted this be sorted out at pre-contract administration stage so we knew what the extra costs would be before we were committed to the contract.
I just wanted to commend you on such a well written and easy to understand response to the question. One of the things that is great about this forum is people being able to share their knowledge.
Having said that, I totally agree with everything you have said. I have been through this on several projects one in parramatta council, one in Sydney council (Alexandria) and one in lane cove council and the experience has been totally different each time depending on what the council was after.
For instance in Alexandria the council's report requirement was for us to model flood levels up to several streets away as they didnt have the flood levels on file and this cost us $96,000 as it involved a lot of complex stormwater modelling.
At the other end of the scale Lane Cove council were simply concerned that our site was in an overland flow path and we managed to deal with it with a small bit of modelling and extra drainage all done by our hydraulic engineer for around $1500.
Then back to Parramatta the flood modelling was very complex and the DA took several years.
So best thing to do is go and get a meeting with Councils Engineers to see what they are after before embarking on the KDR journey.
Your builder is likely correct... Part 3, Division 2, clause 3.5 of the complying development code disqualifies development under CDC for flood control lots... refer https://www.legislation.nsw.gov.au/view ... 72#sec.3.5 so that only leaves the option of a DA.
We ran into a similar issue in that even though we're 32m above sea level there is an overland flow path that clips the front corner of the block. Whilst it was unexpected, frustrating and a little worrying at the time, in the end the main effects were:
1. time delay whilst the house design was altered to suit council's development control plan (which was quite different to CDC)
2. time delay & extra cost for the hydraulic engineer to prepare a flood risk management report
3. time delay for DA approval (5 months for DA vs 2 weeks for CDC)
4. extra cost for raising the slab/finished floor level by 540mm (extra fill, piering and drop edge beams)
For us, I contacted the builders hydraulic engineer (the one who would normally do the storm water system design for the builder) and asked his advice which was...
Go to council and ask for information. They quite likely have done a flood study for the area (otherwise how do they know the area is prone to flooding).
Best case scenario is that council give you the flood levels otherwise they will say what information they have.
Whatever they have, get a copy and forward it to the hydraulic engineer which will help him greatly to do a flood risk management report.
A flood study is a time consuming and expensive exercise so if you can get it from council it is a big benefit for you (both time & $$$).
In my opinion you're best to work with the builders hydraulic engineer for this. The storm water design and the flood risk management report are inter related, you'll be duplicating work if you engage a separate engineer.
The builder may prefer that you sign the contract and sort this out by variation later. I wouldn't (and didn't) do that, we insisted this be sorted out at pre-contract administration stage so we knew what the extra costs would be before we were committed to the contract.
We ran into a similar issue in that even though we're 32m above sea level there is an overland flow path that clips the front corner of the block. Whilst it was unexpected, frustrating and a little worrying at the time, in the end the main effects were:
1. time delay whilst the house design was altered to suit council's development control plan (which was quite different to CDC)
2. time delay & extra cost for the hydraulic engineer to prepare a flood risk management report
3. time delay for DA approval (5 months for DA vs 2 weeks for CDC)
4. extra cost for raising the slab/finished floor level by 540mm (extra fill, piering and drop edge beams)
For us, I contacted the builders hydraulic engineer (the one who would normally do the storm water system design for the builder) and asked his advice which was...
Go to council and ask for information. They quite likely have done a flood study for the area (otherwise how do they know the area is prone to flooding).
Best case scenario is that council give you the flood levels otherwise they will say what information they have.
Whatever they have, get a copy and forward it to the hydraulic engineer which will help him greatly to do a flood risk management report.
A flood study is a time consuming and expensive exercise so if you can get it from council it is a big benefit for you (both time & $$$).
In my opinion you're best to work with the builders hydraulic engineer for this. The storm water design and the flood risk management report are inter related, you'll be duplicating work if you engage a separate engineer.
The builder may prefer that you sign the contract and sort this out by variation later. I wouldn't (and didn't) do that, we insisted this be sorted out at pre-contract administration stage so we knew what the extra costs would be before we were committed to the contract.
Thanks you so much Rob for the detailed information, much appreciated.
Can I please check how much did the $ cost end up being to have the slab raised in point#4 above?
I have reached out to the council to get their flood report which I will take to the hydraulic engineer. The issue could be to do with overland flow path or the drainage pipelines in the area with low capacity to handle a major downpour in a storm like event, but our property may or may not be impacted, only an engineer would be able to advise not the council.
The issue is that we are dealing with 2 builders as part of the tender stage and haven't signed up with anyone yet. It appears that we may have to commit to one of them and engage with their engineers to understand the full cost and time frame implications before signing the contract.
The issue is that we are dealing with 2 builders as part of the tender stage and haven't signed up with anyone yet. It appears that we may have to commit to one of them and engage with their engineers to understand the full cost and time frame implications before signing the contract.
.... and that's why on difficult sites/builds clients engage their own Designer/Engineers and then get 3 Builders to quote.
Forewarned is forearmed
Thanks for the positive feedback Simeon. The forum sure is an invaluable resource... we've benefited greatly from other peoples experience/advice and where our experience might help others I try to pay something back.
parra_kdr, I checked our contract and the cost to raise the slab was $24,875. We required additional fill, piering and drop edge beams around three sides of the house.
parra_kdr, I checked our contract and the cost to raise the slab was $24,875. We required additional fill, piering and drop edge beams around three sides of the house.
Thanks for the positive feedback Simeon. The forum sure is an invaluable resource... we've benefited greatly from other peoples experience/advice and where our experience might help others I try to pay something back.
parra_kdr, I checked our contract and the cost to raise the slab was $24,875. We required additional fill, piering and drop edge beams around three sides of the house.
parra_kdr, I checked our contract and the cost to raise the slab was $24,875. We required additional fill, piering and drop edge beams around three sides of the house.
Hi Rob, can I ask you if your new house Slab is higher than your neighbor's property for your new build? My neighbor on my left did KDR 13 years ago, we are both on flood overflow path, I designed house the same level as theirs, hopefully, it will be ok.my build is at 8.25m height, if I need to increase by 0.4m, it will be a nightmare for me. property was under Hornsby council but it's with paramatta now.
Thanks for the positive feedback Simeon. The forum sure is an invaluable resource... we've benefited greatly from other peoples experience/advice and where our experience might help others I try to pay something back.
parra_kdr, I checked our contract and the cost to raise the slab was $24,875. We required additional fill, piering and drop edge beams around three sides of the house.
parra_kdr, I checked our contract and the cost to raise the slab was $24,875. We required additional fill, piering and drop edge beams around three sides of the house.
Hi Rob, can I ask you if your new house Slab is higher than your neighbor's property for your new build? My neighbor on my left did KDR 13 years ago, we are both on flood overflow path, I designed house the same level as theirs, hopefully, it will be ok.my build is at 8.25m height, if I need to increase by 0.4m, it will be a nightmare for me. property was under Hornsby council but it's with paramatta now.
We have a fall of about 300 to 400 mm from left to right across our property. The floor level of the neighbour on the left is higher than us and the floor level of the neighbour on the right is lower. Unfortunately I'm not sure that will help you with your situation as both our neighbours houses were built about 50 years ago... long before Councils worried so much about overland flow paths like they do these days.
Related
3/12/2023
10
Yes it had a house on it. But Melbourne water only wanted something the original size of the existing house. We managed to fit a 45sq house on.
11/09/2023
3
Give Jonathan a call. Tell him you know me. He is in my opinion the best surveyor I have ever worked with. His number is 0425 285 622 All the best Simeon