Level for Level Flood Plain Compensatory Storage

[jackel74]

Can any one assist in any ideas of taking a flood level and topo and design and working out the flood compensation requirements per increment of 100mm by ground level not cut/fill levels?

and then once these volumes are know is there a way to cut a specific volume from a level band (eg 100.00mAOD - 100.10mAOD) within an area?

The main issue is extracting the level volume information for specific levels etc and the fact it has to be a comparisons between 3 surfaces not 2.

I have attached a PDF of the EA Level for Level Flood Plain Compensatory Storage details should kinda show the issue 🙂

Cheers in advance 

K:)

Karl

[Pointdump]

J,

If you're talking about, say, a pond or retention basin, then Stage Storage will give you some tools to calc different levels. If you're talking about a creek or river, then Hec-Ras or the River and Flood Analysis Module.

Dave

[jackel74]

As a separate/same question, is it possible to create a tin of two surfaces and have that tin at the actual ground levels even though im using a sloping comparison surface to an ogl - this would give the displacement based on the ogl and at what levels and i can then extract the volume if this at the required levels and do this with the ogl compared to design and then design compared to flood levels and try and merge the info lol im sure i am over complicating this 🙂 please help pulling the little hair i have left lol

[jackel74]

Thank you for replying 🙂

Its a bit of a mixed bag as per 😞 basically i have an topo which includes some of the river but not all and a moddeled flood level 1in5/1in10 & 1in25 year flood levels (if they were flat would be easier 🙂 and a design that fits over the topo - 

I have created all the surfaces and worked the overall volumes easily 🙂 its the extracting of the relative volumes for specific ground levels 😞

From what you say i would prob say it is a creek or river but not used the Hec-Ras or the River and Flood Analysis Module so would need to look into that 🙂 do you know if it would br possible to extract these volumes at ground level increments within a site?

sorry for being a pain 🙂 but finding it differcult to get my head around it 😞

Cheers  k:)

[Pointdump]

J,

"...its the extracting of the relative volumes for specific ground levels"

That would be the tough part. That's backwards to the usual work flow. Normally you have data, Manning n and flow numbers, for 100-year or 500-year events, and you plot the new shoreline on your topo map.

Anyway, here's a really good overview of Hec-Ras by Andy Carter. 3 videos, about 5 minutes each:
https://www.youtube.com/watch?v=DpMvnvoTKUA

And if you're on subscription you can download the River and Flood Analysis Module.

Dave

[jackel74]

thank you 🙂 and yes everything i seem to do is backwards to the norm lol and no im not on subscription as yet and not sure looking at it that its what i need 🙂 the flood levels have already been calculated using hec-ras and showing the flood lines are easy as i would just set the o contour on the cut/fill but its the volumes im trying to extract to place at the same levels elsewhere but it seems the only way would be manually 😞 thank you for helping anyway 🙂 k 🙂

[Pointdump]

J,

"...is it possible to create a tin of two surfaces and have that tin at the actual ground levels"

Maybe. In Grading you can use Infill to create a Surface using your highwater marks (flood lines) as a Boundary. Then you could use the Volumes Dashboard to give quantities from OG. Theoretically, of course.

Dave

[KirkNoonan]

The easiest way we've come up with to do flood plain compensation is a combination of methods. You're right, since you are comparing a slice between 2 elevations, it is difficult to use the prescribed volume workflow. We use stage-volume reports to get the numbers at the range you need and trial and error to get the right shape of compensating storage. it is easy enough to get the volume numbers, but coming up with the right size and shape of cut while also keeping your banks stable is the art.

You could probably do something with a volume surface that compares the pre with your post and limit the elevation range to be the compensating sotorage range, but I think it would be about the same amount of work. 

[jackel74]

will the stage-volume reports give me volumes at ground levels or relative to the comparison surface? because would that not just give me a relative volume not volume per level? sorry i used to do this years ago by hand - but this site seems very complicated due to the sloping flood levels - to used to making surfaces for each individual aspect lol

Also is stage-volume reports not for basins? the problem is this is a topographical survey and no specific basin or would you use the topo as the basin and the sloping flood level as the reference? and would this take into account all the undulations of the land or just work in specifi areas 🙂  sorry used to old CAD lol 🙂 

cheers k 🙂

karl

[KirkNoonan]

You're right, I need to re-phrase a little to get from what I was thinking to what it is actually called in the software and to how it should look in the current version's workflow.

Firstly, the volume comparison just gives you volumes where the surfaces overlap. You should make copies of each of your surfaces and could put a boundary around them if you don't trust it, but it is generally pretty good at doing what I want.

By copying the surface, I mean to create a new surface and right clicking on edits under the definition and choosing 'paste surface' that gives you a copy that remains dynamically linked to the other surface that you can then refine further to only include min and max elevations that meet your compensatory fill requirements. Do that with both surfaces and then do the volume analysis on the analysis ribbon. That should give  you the balance between the pre and post surfaces at the elevation range you're looking for. If I had the required data handy, I'd make you a fancy video to demonstrate. Since I don't, give it a whirl and continue to ask question here about the steps I forgot to metnion 😉

Kirk

[jackel74]

ok i think i know what you saying 🙂 not tried this before so should be fun 🙂 **** i know soo little about this software nowaday 😞 how things change 🙂
so if i change the base level of one of the surfaces and the top level on the other linked surface on each set then do a volume calc it will workout all the aspects of the merged sites? I think i need to play a bit on this to get my head round it 🙂
cheers for your help 🙂 muchly appreciated 🙂

[KirkNoonan]

Set the top and bottom range. You probably only need to do that on the proposed, but I usualy do both.

[Pointdump]

Karl,

You might want to thumb through the River and Flood Analysis Module Users Guide. (I'm reading it right now.) The Hydraulic Calculator looks like it will do what you want, i.e., calculate Flow discharge for a specified normal depth or elevation. (Stage Storage for Sloped Terrain)
http://forums.autodesk.com/autodesk/attachments/autodesk/66/292700/1/Autodesk%20River%20and%20Flood%...

Dave

[KirkNoonan]

We're not really worried about flow or dischrge for this. It is about creating storage in the floodplain (usually the area between wet season groundwater table and the 100-year flood elevation) to make up for any storage that has been displaced by fill or buildings. In many cases it is necessary to model the flow through the new channel, but for the volume calcs, Civil 3D get the job done fairly well. Easier than by hand, anyway.

[fcernst]

I would use a multi-level Corridor model. Then you can simultaneously design and compare material volume shapes (displaced volume vs. compensatory volume) at each Alignment station per each elevation level.

[jackel74]

I was looking at the level adjustments previously but when i did do it it seems to work out the volumes differently but it was obviously something i was doing lol and i always need to display what is happening for my own piece of mind 🙂
im obviously out of my depth as i dont know how to paste the surfaces lol I wil need to do some research i feel lol thanks soo much for you help i think i need some serious training lol

[jackel74]

I think if i were doing the whole project it would be a direction to go but i am only trying to help out a friend on a project and not used the new versions of CAD and all the new functions are beyond me at this time 🙂 thanks for looking 🙂

[jackel74]

to be honest until i can work this out it may be quicker for me to create sections (i would look at the corridor option as fcernst suggested but still looking into all these new features and think it will take me longer to workout the corridor option and set up all the aspects but it is something to look into for future 🙂

[jackel74]

a friend did suggest In Civil you need to have a topo surface or design surface first, then you need to create a separate surface for each level you want to analyse. You then need to create TIN volume surfaces for each capacity level and minus the numbers of subsequent elevations from that table in order to get your 'per level' capacity. does that make sense?

[jackel74]

a friend also said As I said, for level by level you need to create multiple copies of your 'flood level' comparison surface and then run through the iterations at each level. The volumes will be cumulative, but in excel you can then minues each from the total and that will leave you with your storage at each level - but again im not getting how this would be level for level as the comparison is relative to the sloping flood - im really messing with myself on this lol wish my brain would get round this 🙂