Calculation of flow capacity at bank height

[inou-730]

Helllo HEC-RAS Users
I would like to compute the flow capacity at both bank elevation for each cross section. Usually for this computation, I have conducted several profiles (10, 20, 30, ... m3/s) and plot a stage-discharge curve, and on the graph read the discharge at the bank elevation. This case , the stage-discharge curve is affected by downstream or upstream conditions.

Now I would like to compute the flow capacity at both bank elevation for each cross section independently. Which I mean, compute the hydraulic radius at the bank elevations and give a certain energy slope for each cross section. And by Manning, I will calculate the discharge. In HEC-RAS is there a menu that I can input energy slope to compute the flow capacity at the bank elevation ?

thank you for your attention.

[jarvus lunt]

I am not aware of a menu to do what you want, but it shouldn't be that hard to do on your own.

You can use the known water surface elevations at a given cross section to force RAS to give you the water surface(s) at the bank elevation(s) for each cross section. Put in some dummy flow such as 1.0.

Go to the profile output table. Under Options, select Define Table. From the list of variables shown, double click on Conv. Total. This will then give the total conveyance at each cross section. Highlight the entire column by clicking on the top of the table. Copy and past this into a spreadsheet. The total flow can then be computed from

Q = K Sf^0.5

Where Q is flow, K is conveyance, and Sf is your desired fricton slope.

[inou-730]

Dear Dr.jarvus lunt
Thank you for your reply. The second paragraph is a solution for me , but could you explain what to do ? How can I give HECRAS a kown waterlevel for each cross section ?

regards

[jarvus lunt]

From the steady flow data editor, click on options and select Set Changes in WS and EG...

Select a river station, click on the <Known WS> button and enter the elevation.

You have to select each river station by hand (takes a little time), however, here is another short cut.

Run your data set.

Go to the profile output table and select define table. Find the variable LOB Elev. Double click on this. This will give you the elevation at the left channel bank. Click the top of this column to highlight the entire column and copy it into the clipboard (Ctrl c). Go back to the <Known WS> editor. Go through adding each river station, but don't enter the elevation. After all the river stations have been added, click the top of the column and paste in the elevations (Ctrl v). If you have any bridges/culverts in your data set, you may have to account for that when you paste the data back in.