topic Re: need to create polygons (basins) that are at a specific elevation, for a flood in Water Resources Questions

need to create polygons (basins) that are at a specific elevation, for a flood

EtoileJensen — Wed, 20 Jul 2011 22:05:12 GMT

I am in desperate need of some help. I???m in over my head. I hope someone can throw me a life line.

What I need to do is create polygons (basins) that are at a specific elevation, for a flood event, within a number of different watersheds.

???I have a DEM of the area, which I have created the watersheds and depression basins from.
???I have the volume for each depression and its top elevation within each watershed, along with a spill/pour elevation for the watersheds.
???I have a volume (not an elevation) for the flood event for each of the watersheds.

I need to create an ???event basin??? for each of the watersheds. (Don???t worry about watersheds that have a depression volume less than the event volume)

I am using ArcEditor 9.3 and have the following extensions: Spatial Analyst, 3D Analyst and ArcHydro (which I have never used). (I had felt pretty competent in Spatial Analyst till now.)

If you could give me some step by step instructions, or the equation I need to use, to create a raster of the new elevations it would be GREATLY appreciated!

THANKS!

Re: need to create polygons (basins) that are at a specific elevation, for a flood

MattMead — Thu, 21 Jul 2011 02:16:12 GMT

If I read what you posted right, you have a total volume of water for each flood event(basically treating this as a reservoir where you know the total inflow), the depressional areas and their volumes(reservoir storage volume) and you need to calculate the corresponding elevation and then map that?

If so, this may not be the best way, but it should work...it could possibly be time consuming though:
Basically what I'm outlining below is a process by which you can calculate a flood elevation based on a stage-storage relationship. I've assumed you have total volume of the depressions, not a stage-storage relationship. If you do have the storage volumes broken up by elevation, you can skip the first couple steps.

You will need:
3dAnalyst(can probably use spatial, but i have more experience using 3d)
Excel or similar spreadsheet software
EZ profiler
TIN Intersect
links are included below

1) Using 3dAnalyst, calculate the stage-storage relationship.

A) Create a polygon shapefile with attributes representing known elevations within your depressional areas. Draw a polygon containing your depressional areas. I'd suggest every foot(or meter depending on your units) unless you have huge depressional areas that are very deep in which case a larger "step" may be appropriate.

B)turn the polygon into a TIN for each of your stages

C)convert your terrain DEM into a TIN

D) use Intersect TINS command (http://edndoc.esri.com/arcobjects/8.3/Samples/3D%20Analyst/Surface%20Analysis/Intersect%20Tins%20Command/Intersect%20Tins%20Command.htm) to generate a polygon with volumes. There will be 3 "codes": above, below and same. If you set the 1st TIN in the command to be your elevation polygon TIN and the 2nd to the terrain TIN, "above" should represent your depressional areas. Do this for each elevation. start an edit session and delete everything not "above."

2) export these new volume polygons to excel using EZ profiler (http://arcscripts.esri.com/details.asp?dbid=16031) Other tools can do this, but this is the one I generally use. You cannot export more than one at a time so copy the data into a different workbook as you go.

3) using your storage volumes in excel, create a plot of the storage volume at each stage.
A) just add up the volumes from each of your volume polygons for the X axis and use the known elevation for that volume on the Y-axis.

4) using your known flood volume determine where that intersects the stage-storage curve and that gives you the flood elevation.

5) using your polygon from step 1, assign your new flood elevation, convert to TIN and use intersect TIN command again. Everything that is "above" or "same" should be your flood event inundation area"

6) I guess you said you want that as a raster so convert that polygon to a raster...I think that is in the conversion toolbox. I'm not at my work machine, so I cant check.

repeat for each watershed.

If this doesnt do what you were asking, let me know and I'll see what I can do. I'll check periodically tomorrow to see if you have responded.

Re: need to create polygons (basins) that are at a specific elevation, for a flood

EtoileJensen — Thu, 21 Jul 2011 12:41:00 GMT

Wow Matt I'm impressed. It sounds like you hit everything right on, except I don't need a raster for the polygons.

I am still digesting your instructions. The only real problem I see is that I have nearly 1000 depression basins to do this for. I may be here for awhile

I was totally on the wrong track; I thought this could be done using the fill command or the raster calculator to compare two different rasters.

I also thought that ArcHydro might have a tool to do it. (anyone??)

I will work thru your directions today on my pilot project area and wait and see if someone has another suggestion for the entire area.

Thanks so much for being so willing and able to help others.

Re: need to create polygons (basins) that are at a specific elevation, for a flood

MattMead — Thu, 21 Jul 2011 13:17:01 GMT

Ouch, I hope someone else with a better idea does come along.

I just did some more poking around and it looks like Spatial Analyst has Cut/Fill which also gives you volumes according to the esri help page on it. Its in Spatial Analyst->surface->Cut/Fill

That would save you the errors that would be included during the raster->TIN conversion.
Also, I think you would be able to do them at a larger scale if you did it with Cut/Fill. You would still need to create rasters for each of your "stages" but then could possibly be larger and cover more than one area.

I've never used ArcHydro so I dont know what all it is capable of doing so there is some hope there at least.

Re: need to create polygons (basins) that are at a specific elevation, for a flood

MattMead — Sat, 06 Aug 2011 00:38:24 GMT

Are you still working on this? I think I came up with a way that you could automate most(if not all) of it in Model Builder. If you are, let me know and I'll work out the details and get it put together.

Re: need to create polygons (basins) that are at a specific elevation, for a flood

tientai_huaftientai_huaf — Tue, 04 Oct 2011 07:56:01 GMT

Hi! Meadmw. Can you tell me detail method of you, please? What software do you use ?
Thank you very much !

Re: need to create polygons (basins) that are at a specific elevation, for a flood

iankirschner — Mon, 25 Mar 2013 14:02:11 GMT

Hello

I am doing a similar project to ET_oile. I need to create flood polygons. I have a depression less DEM for the water shed area. I have known water level and corresponding flow rates from a water gauge stations in the center of the city. I am having difficulty figuring out the ArcHydro tools. Any suggestions on the work flow and specific tools I should use to create accurate flood polygons for different water levels?