Linking Hydrological modeling with Hydraulic modeling

[Myla-RaeBaldwin]

Hi, I am working through a flood modeling project as part of an academic course and attempting to use both ArcHydro and HEC-GeoRAs. Does the watershed delineation process using ArcHydro produce data that is then a necessary input for hydraulic modeling? Are the two modeling processes ever linked or are they usually used for very separate outcomes? I am also wondering if the river schematic produced from the stream definition tool can be used to guide the digitization of the river centrelines in Arc using HEC-GeoRAS.

Thank you for any insight that can be provided.
Myla-Rae

[MarkBoucher]

Myla-Rae,

Does the watershed delineation process using Arc Hydro produce data that is then a necessary input for hydraulic modeling?

Arc Hydro is used for watershed delineation for hydrology analysis and does not link to hydraulic models.

A "partner" program, one that is like Arc Hydro is HEC-GeoHMS. This is also developed by ESRI for the US Army Corps of Engineers (you can find its free download on the USACOE HEC website). GeoHMS is used to perform the watershed analysis like Arc Hydro and then create field in different datasets that will be used to export HEC-HMS modeling files. The HEC-HMS can be used to actually run the hydrology analysis (calculate hydrographs).

Similarly, HEC-GeoRAS (also developed by ESRI for the USACOE) uses Arc Map data to eventually export to files that can be used by HEC-RAS to perform open channel flow calculations (calculates energy and hydraulic grade lines). GeoRAS can also import RAS output back in to Arc Map for display of the results of floodplains, etc.

The only data links that I can think of is a data storage system (DSS) developed by the USACOE for the HEC programs. It is the DSS format. HMS saves it output to a .dss file. RAS can read the .dss file data. This is very handy for unsteady flow analysis in RAS. The DSS format has nothing to do with ESRI products as far as I know.

I am also wondering if the river schematic produced from the stream definition tool can be used to guide the digitization of the river center lines in Arc using HEC-GeoRAS.

The drainage lines created using Arc Hydro will be "jagged", that is, thy are created going from raster grid center to raster grid center. They will not be smooth lines and I would not use them directly for GeoRAS. If you have a very very fine DEM, you could possibly smooth them out, but I suspect that a very fine raster would result in more sinuosity of the thalweg and still not be appropriate for RAS modeling.

You should read up on the RAS modeling. You will likely find that the channel length used in RAS modeling is supposed to follow the "center of mass of flow", not necessarily the "center line" though the center line is probably very close.

Cheers!

Mark

[Myla-RaeBaldwin]

Thanks very much for your reply Mark. I think my team members and I got ourselves a little over our heads with this project, trying to learn HEC-RAS without any hydrological background. In my research I have discovered that many of the decisions that need to be made using HEC-GeoRAS requires a certain level of hydrological knowledge. If we just want to show three possible flood extents over a terrain based on a high, average and low river flow levels over a ten year period, is it possible to do this using only ArcHydro tools? Or does mapping flood extents without having river geometry at our disposal, (only river gauge readings and a DEM) make it necessary to use another software suite such as HEC-RAS/HEC-HMS?

Again, thanks for your timely reply,
Myla-Rae

[MarkBoucher]

You can do some approximation using relative water levels. This thread was posted very recently and addresses that.
http://forums.arcgis.com/threads/79620-Calculate-maximum-flooded-area-based-on-maximum-flood-levels-...

[Myla-RaeBaldwin]

Thank you for pointing me to that link.
Very helpful. HEC-RAS will be tackled later while I explore this avenue.
Thanks,
Myla-Rae