Bending channel

[Caroline]

Hi,
I have a model of a channel with mostly vertical walls. For most flow cases, the water surface is below the elevation at which I put the bank stations (situated on the walls). When the channel bends I used the LOB and ROB data to adjust the model.

But the question is: does HEC-RAS understand that the channel bends when the flow goes in the main channel and the overbanks are dry?

Should I change the position of the bank stations, and where should they preferably be placed?

Caroline

[Chris G.]

Hi Caroline-

Excuse me if you already understand this, this next paragraph is for others who may not understand how RAS deals with bends.

Please keep in mind that RAS is a 1-D model and it does not explicitely calculate any effects from a bend (i.e. added turbulence, super elevation, etc.). That being said, there is added friction loss on the outside of a bend, because RAS uses the longer reach length (i.e. for a left-hand turn, the right overbank will have a longer reach length). For the same reason there is less friction loss on the inside of the bend, because it will have a shorter reach length.

If the flow remains between the bank stations through the bend, RAS only uses the main channel reach length to calculate friction loss, so the added friction length on the outside of the bend and the subtracted friction length on the inside of the bend is not accounted for. So the answer to your question is: No. But, if you wanted to put bank stations inside the channel to somehow simulate the variation in friction length loss due to a bend, you can.

[Author]

Posts