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| GeoCommunity Mailing List |
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| Mailing List Archives |
| Subject: | GISList: SUM: Plotting water surface profiles |
| Date: |
11/05/2001 12:14:33 PM |
| From: |
Chad E. Sperry |
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Thanks to everyone for responding to my original question. I also received
many inquiries into the responses I received. The response from Dean Djokic
came the closest to understanding the nature of my question and providing a
workable solution. He suggested using HEC-GeoRAS, the only problem with
using GeoRAS is all of the setup required. I would like a simple extension
that delineates a floodplain from inputting only upstream and downstream
elevations, but it should calculate a true linear sloping profile (not just
a flat pool elevation). Dean also suggested writing an avenue script to
accomplish this, I was wondering if one already exists.
Thanks again.
Chad
Original Question:
Does anyone have experience/advise in using GIS (ESRI-based) to plot a true
sloping water surface profile from elevation data (TIN/GRID/or other)? We
have used HEC-GeoRAS, but would like a solution that integrates or at least
breaks the profile into a user specified interval (base flood elevation) to
calculate the flooded area with only inputting know upstream and downstream
elevations and extents.
Responses:
1. Dr. Dean Djokic:
The only true sloping water surface profile can be obtained through
hydraulic model, as you were doing with HEC-GeoRAS. The water surface
profile is not linear, so giving just upstream and downstream known
elevations, without knowing the changes between them, cannot give you
an accurate representation.
You also have to know the cross-section cut lines, as these can change
significantly between the end cross-sections and affect the final
delineation.
You can use the GeoRAS extension and define the elevations manually.
The post processing in GeoRAS has three steps.
1) Retrieve the cut-lines and modeled WSE from the RAS model.
2) Generate the WS TIN from that data.
3) Get the floodplain by intersecting the terrain and WS TIN.
You can manually define the cross-sections and WSE, and then run
steps 2 and 3. If you have the cut-lines as a shape file, you can
write a simple Avenue script that will take the WS elevation at the
top and bottom cross-sections and linearly interpolate between them,
using distance between the cross-sections as a measure. As I mentioned
earlier, this is quite a strong assumption and might get you in trouble
for any but roughest estimates.
2. Lynn M. Ray:
I would suggest that you try Spatial Analyst, if you have it. If not,
there are several scripts that can help. I have attached one. I haven't
tried this one myself. Hopefully it is close enough to Spatial Analyst.
3. Arun Saraf:
Yes! it is possible. Use Profile Extractor (available on ESRI Script site).
Theresa Olsen
Look into the SURFACEPROFILE command. Can be used in the GRID and ARCPLOT
modules. We have been using HEC-GeoRAS also and this command has been very
useful in the QA process.
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