1D Steady Flow

[Dhavalkumar Patel]

Hello, I just started to use HEC RAS software, I do have theoretical knowledge like what HEC RAS software is and all features. I never work as a professional level on HEC RAS.

I am working on project. In which property owner wants to build driveway to connect his home from main road (14′ wide). There is one natural creek( Spruce Run) going through that driveway. I have 1240 drainage area if I consider driveway point as my project location and I am getting 100 year flow from Stream states around 1810 CFS.

Now, I am trying to run HEDC RAS software to get water surface elevation at that point so I can find what should I put along with driveway ( Bridge or Culverts) which would not affect to floodplain and flow.

I only have drainage area number (1240 Acre) and cross section for only driveway location.
Can anyone help me that how should I get require data and How can I find water surface elevation at that point?

I can share detail as much as I have about this project if anyone can help. I also would like to learn more about this software.

[Anonymous]

If you need terrain data check this link below for some sources of data

You can also use QGIS mapping software (free) to do some catchment analysis to work out your flows.
I hope this helps.

[Scott Miller]

Spruce Run, New Jersey , or Oregon, or somewhere else? Does pertinent code call for using HEC-RAS?

I wouldn’t recommend using Stream Stats unless the area was totally forested. And even if it’s a totally forested area, a regression model yields iffy results. The standard error on Stream Stats is usually fairly high. Be sure to account for it.

Are you modeling steady state? Peak flow is usually fleeting, so steady state does not make sense. Use a hydrograph, or a continuous model for the 100 year storm.

[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.

[Anonymous]

Thank you for reply.

I have totally forest area and Spruce run located in Frederick county, Maryland.
My concern is, I do not have enough data to run HEC RAS. I only have drainage area and topography map and point elevation for drive way where I am designing something over crossing Spruce run. In 1240 acre drainage area there is one tributary called spruce run also. this junction is 1345 linear ft away from project location and around 40 ft high as per topography map.
So because of lack of cross section data, I am just putting schematic from junction to project location. and giving peak flow upstream at junction (1810 CFS) and downstream at project location.
I am not getting idea that how I can get all other information to get water surface elevation by HEC RAS. As per my understanding I need Cross section, boundary condition, etc.
Can any one help me to get right direction to figure it out?
[email protected] is my email, you can reach me on my email too.

Thank you.

[Anonymous]

Here is what I did as per my thinking, I have drive way cross section data which I can use as my stream cross section for some points. then I copy this cross section and give elevation difference as per topography map and create other 8 cross section upstream.

I have this two error coming in all cross section. I have 9 main cross section around 120 ft apart. and then I did 30 ft interpretation between upstream and downstream cross section.

I am running steady flow with downstream Boundary condition ( Normal Depth = 0.0091).

error:
1) The energy equation could not be balanced within the specified number of iterations. The program used critical depth for the water surface and continued on with the calculations.
2) During the standard step iterations, When the assumed water surface was set equal to critical depth, the calculated water surface came back below critical depth. This indicated that there is not a valid sub critical answer. The program defaulted to critical depth.

please help to solve this error.
Thank you.

[Anonymous]

Spruce Run, Frederick County Maryland

[Scott Miller]

I take it you are using normal depth with an energy slope = 0.0091 as the downstream boundary condition. The errors you listed are a pair that come up together. Solving one ought to take care of the other. Check the number of iterations that are being used. It can be set as high as forty.

Take a look at where the energy equation is problematic. Is it at the stream crossing, or somewhere else?

Contraction and expansion around a stream crossings have to be handled a certain way. Take a look at this site: https://www.civilgeo.com/knowledge-base/hec-ras-culvert-cross-section-locations/

What does state or county code say, for guidance or requirements? Allowable headwater or required freeboard above the 100-year flow, aquatic organism passage, and other requirements may affect your sizing. How might beaver activity affect the crossing?

The approach you have taken appears to be reasonable, using a topographical quad map and interpolating cross-sections. At a mild slope I’d be looking at downstream controls to see if they affect the tailwater.

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