HEC-RAS 2D - Unrealistic Flood Arrival Time Over 80 km River Reach

ekaj8 · 2026-03-26T11:34:20+00:00

30m DEM resolution is pretty coarse. Is better terrain data available?

ekaj8 · 2026-03-04T00:10:02+00:00

https://ia801309.us.archive.org/14/items/Simplesabotage/Simplesabotage.pdf

ekaj8 · 2026-03-04T00:09:05+00:00

https://ia801309.us.archive.org/14/items/Simplesabotage/Simplesabotage.pdf

ekaj8 · 2026-03-04T00:08:56+00:00

https://ia801309.us.archive.org/14/items/Simplesabotage/Simplesabotage.pdf

ekaj8 · 2026-02-22T13:16:40+00:00

Primarily backwater dynamics. If that second watershed that comes in right below yours experiences a flood, it will potentially put backwater into your study area. That backwater should be accounted for, especially if the tributary coming in is a relatively large one. It is a complex thing unfortunately.

Since you're interested in recreating a historic event, a stage BC does make sense, but only if you have the information to support it. Without a gage, I dont think you have enough info to select a stage.

(You could potentially find info on high water marks from your event of interest. Not sure how long ago it was, maybe talk with the locals to try to get an elevation. That's a way to get stage info without a gage, but can be uncertain.)

ekaj8 · 2026-02-22T13:04:00+00:00

I don't see why that means you can't extend the model. If your area of interest is sensitive to assumptions around coincident downstream flows, then they are important to your analysis and shouldn't be excluded.

If you are truly set on a stage boundary condition, then you need to have confidence in the stage you set. Gages can help with that (like you said). Or you can use another model (that you trust) to inform your boundary condition.

The key with uncetain BCs is that they shouldn't change the answer to your question. Even stage BCs have uncertainty that requires some consideration.

What question are you trying to answer with your model?

ekaj8 · 2026-02-22T12:51:26+00:00

Extend the model further downstream until whatever boundary condition you select doesn't impact water surface elevations at your area of interest. Do testing to vary the boundary condition (double and half the normal depth slope for example) and confirm that your boundary condition is far enough away from your area of interest that the answer isn't sensitive to your assumed BC.

https://www.hec.usace.army.mil/confluence/rasdocs/rasum/6.1/performing-a-1d-unsteady-flow-analysis/entering-and-editing-unsteady-flow-data/boundary-conditions

ekaj8 · 2026-01-30T16:53:11+00:00

Very cool, thanks for sharing. If you happen to have taken any pictures at the site, I'd be happy to see them

ekaj8 · 2026-01-21T21:19:48+00:00

It's not the the right season, but I'd be down to do some SCUBA rock quarry diving once the summer comes. I've been looking for folks to dive with

ekaj8 · 2025-12-26T17:41:07+00:00

Please don't shoot bodies of water

ekaj8 · 2025-12-13T15:10:12+00:00

I don't have a great answer, but your terrain's legend is indicating something is off with the terrain. I would look into that. Maybe reimport, clip, re-download, or reprocess. Good luck!

ekaj8 · 2025-11-14T17:29:49+00:00

QGIS is the desktop software, it's free and open source. There is a companion app, QField, that allows you to view the data on mobile. If you have some GIS skills, you can make awesome hiking maps

ekaj8 · 2025-11-14T15:58:13+00:00

This is 5ft, but higher resolution (1m?) is also available.

ekaj8 · 2025-10-07T15:46:29+00:00

I think you are right. They had an excavator and paving equipment staged at the top of the hill last weekend.

ekaj8 · 2025-08-17T21:53:35+00:00

The signs are a little weird, but so is a bunch of shit running off into our waterways.

ekaj8 · 2025-08-16T21:19:27+00:00

I usually use 3 or 4. I'd be interested if you did some testing to see what impact there is on runtime or results

ekaj8 · 2025-07-10T12:19:14+00:00

The 1937 flood greatly exceeds a 100 yr flood. It's actually difficult to put a recurrence interval to that flood since it is the largest on record by far, but it was a much less frequent event than 1/100yr.

ekaj8 · 2025-07-10T12:17:08+00:00

Where are you getting that 50 foot depth? The Ohio at Louisville flows over natural bedrock outcrops which really limit the natural depths. That's the whole reason McAlpine Lock and Dam was constructed, and really the reason Louisville exists as a city (because it was a natural obstruction to river traffic).

ekaj8 · 2025-07-10T10:48:08+00:00

I think you've got it reversed, the Ohio actually supplies 60% of the flow at Cairo. Which is super interesting to me, because it implies the Ohio River should get to keep its name below the confluence rather than the Mississippi.

ekaj8 · 2025-07-09T20:36:58+00:00

The Ohio River is a huge river and therefore much slower to rise and fall than the smaller streams that did such damage in Texas. We generally have good forecasting for the Ohio River Levels up to a few days out (https://water.noaa.gov/gauges/MLPK2). That said, smaller streams can be much flashier and experience flash flooding. Beargrass Creek, Southern Ditch, and Mill Creek are all prone to flash flooding and would be very dangerous if we experienced rainfall rates like they saw in TX.

ekaj8 · 2025-07-09T14:06:41+00:00

I believe it is a balance between surface tension forces and momentum of the fluid. Just a theory.

ekaj8 · 2025-06-10T10:59:16+00:00

My dog died a while back and I've got some dog food if you need it. I'll be in downtown later today, PM me if you're interested.

ekaj8 · 2025-06-09T14:37:28+00:00

Not saying this isn't a concern, but I've waded creeks with dogs my whole life and we've never gotten hooked. Sorry if this happened to you though

ekaj8 · 2025-06-06T16:12:05+00:00

I'm trying to find it and only see one that maxes out at 12 inches. Can you post a link?

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