[cameron]

Probably your time step is way too high.

[cameron]

One other thing you could try is adjusting the weir coefficient for the lateral structure or switching to the 2D equation option instead.

[cameron]

It is important to note that HEC-RAS will use half the number of cores you have on a machine if it is left at the default of using all cores. So when you say you have 16 cores, it is only using 8.

If you use a land cover dataset for manning’s or override regions it should not make a single difference if they are identical as all they do is apply a n value to the cell face.

You could do a test to see if the same manning’s are getting applied as 5.0.5 creates a final n value raster. Just do a subtraction of the two in GIS and see which areas are the same or different.

If you can identify the cells that are iterating a lot, fix them and that will help with run times. I have gotten runs that at the beginning took 12 hours to run down to 1 hour

[cameron]

I have found that culverts in 2D do not like backwater and can cause instabilities so be careful. I agree that smaller time steps help or having the culvert cover only one grid cell

[cameron]

I would say that the 0.2 value for weir coefficient might be too low. The value the HEC-RAS manual uses is for a lateral type of flow that is spilling out of a channel. It is not meant for channel type flow. Think of more like an inline weir which can have values up to 2.6 to 3.1.

[cameron]

using the rules boundary condition maybe

[cameron]

was the 1D/2D iteration option turned on?

For the lateral structure what did you use as the weir coefficient?

Did you try breaking up the lateral structure into more pieces?

[cameron]

Can you share the files?

[cameron]

can you post a screen shot of the error?

[cameron]

HTAB parameters for the culverts in 2D? In the Connection Data Editor there is no option for HTAB.

There is no 1D in these models so no HTAB.

[cameron]

Did you add flows for them? Do they have different names?

[cameron]

I have tried using the variable time step with Courant and with it off.

For the Froude mixing coefficient are you talking about the Eddy Viscosity or the something else? I usually don’t use the eddy viscosity, but can add it in to test it.

I have not yet isolated the 25 bridges, but that is my next step. With a time step of 0.1, some of the bridges give ok results now so I am skipping those. I am placing a flow upstream each bridge one by one and testing different things to try and fix each problem structure.

It is full 2D model and the DS boundary condition is a rating curve from a 1D FEMA model which is 1 mile downstream the closest bridge and 2 miles downstream the project area.

I plan on running about 2,500 runs so I need to optimize the model to run fast.

[cameron]

Stream stats is ok for a lot of applications and is free. The error may high, but so is any other hydrology method unless you have calibration data which most studies do not. For FEMA studies, regression is perfectly fine and people do it all the time. Generally what happens is if you don’t have calibration data, you calibrate the hydrology model to the regression flows so you end up getting the same value anyway.

Depending on the situation, if the stream stats flows work for what he is doing great. If they feel they can get a lower discharge from a calibrated hydrology model and want to spend the money to develop it, even better.

[cameron]

We are modeling up to the 3,000 year event for some probabilistic modeling so all bridges are impacted.

[cameron]

Does it say there is an error with the mesh? Did you have both Mapper and the Geometric Editor open at the same time?

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