Browse Forums General Discussion 1 Jan 07, 2016 5:36 pm Does anyone know the calculations to work out how high my floor needs to be raised from the ground if my property is in a flood zone? I current have an AHD survey booked in, and am planning to go into council tomorrow to submit a Flood Floor Level certificate (takes 14 days).. but while I was on the phone to the council I asked for the information over the phone. The engineer verbally told me: AHD is 2.45 Flood Floor Level is 1.95 Masterton is building a house in the street behind us (and closer to the water) and they said it had to be raised 1.2m I am worried that the guy mistook my question and was telling me I had to raise the floor 1.95m, but I am sure he has done this enough to know the information I am asking. But my understanding of the number provided would mean my house would only need to be raised 500mm ? Blerg, guess I will wait for the 'official' documents, but was just curious about the formula. Re: Flood Zone AHD 2Jan 07, 2016 6:14 pm What state are you in? I don't know the formula, I just know that the flood overlay on our block turned into a 4-5 month saga, trying to get our planning application approved by Melbourne Water!!! That was before it even went to council. Make sure your builder understands the process! Re: Flood Zone AHD 3Jan 07, 2016 7:00 pm Re: Flood Zone AHD 4Jan 07, 2016 7:02 pm Re: Flood Zone AHD 6Jan 10, 2016 11:02 pm Hopefully you don't have too much trouble with your flood overlay. We did. It wasn't just the slab height we had to consider, although we didn't know that at first.....We had our planning application knocked back because the report came back saying we need at least 3m set back on our eastern boundary - for the floodwaters to escape apparently! We had to start all over again. All up, between the 2 planning applications it took almost 4months to get consent to build and then it had to go to council! Re: Flood Zone AHD 8Jan 11, 2016 1:45 am Just be aware that most authorities use historical data that is now effectively redundant for storm events and wind. This is a world wide issue. 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Flood Zone AHD 9Jan 11, 2016 7:19 am "The Australian Height Datum is a geodetic datum for altitude measurement in Australia. According to Geoscience Australia, "In 1971 the mean sea level for 1966-1968 was assigned the value of 0.000m on the Australian Height Datum at thirty tide gauges around the coast of the Australian continent." In Sydney that is taken at Fort Denison, smack bang in the middle of Sydney Harbour and can vary from a low of 0.3m to a high tide of 2.0m ( roughly ). All it means is that the councils are making sure ( climate change sceptics look away now ) that with rising sea levels your house will be flood free for many years. Quote: We had to start all over again. All up, between the 2 planning applications it took almost 4months to get consent to build and then it had to go to council! Who are these clowns you are building with? The first thing I do when a client signs on the dotted line to get me to draw plans for them is look up their address on the relevant councils website and note any restrictions on the site. Heights, setbacks, heritage items etc. The flood zone restrictions would have stood out like the proverbial and anyone drawing your plans should have been aware of what was required from the get go. Here's a rough drawing of your levels... http://i1212.photobucket.com/albums/cc455/stewiesno1/Picture%201_zpsjrssddo5.png Porch and Alfresco to their relevant levels Quote: In vic, generally have to build 300mm above the flood level That would be a general guideline only I'm sure. Topography of individual sites relating to the local area plus which particular council you are in would have far greater impact on your design. Stewie Re: Flood Zone AHD 10Jan 11, 2016 8:01 am They knew there was a flood overlay but yes, we were disappointed that no one knew about the boundary setback before the permit was applied for. I guess we can also take some blame but we didn't have a clue about any of these processes....as the old saying goes "you don't know what you don't know". They seemed to have the slab height figured out and that was all we thought it involved at the time. Re: Flood Zone AHD 11Jan 11, 2016 8:04 am But thanks Stewie, your clients are lucky...... It has been a challenging time but I don't want to dwell on what's happened. I'm trying to look forward to what's ahead. Hopefully it's all positive now. Re: Flood Zone AHD 13Jan 12, 2016 9:44 am braddy_ ..... but was just curious about the formula. You can look up water engineering text books for simple flood formulas, unfortunately these have proven less than accurate. The calculations nowdays are complex and involves many variables , 3D modelling with differential calculus (rate of change over time) simply put "computer multiphysics simulations" Ironically, all those expensive homes already built below standard in high risk areas will end up paying one way or the other through increased insurance premiums. Other examples, coastal - wind, forest -fires, etc,etc Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs 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. 10 33606 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 3 12288 5 6777 |