Later flows in Quasi-unsteady flow data

[JohnLonergan]

So, I am doing a sediment transport project which I have another thread running on for other problems.
Basicall I have an abstraction taking place at a weir but it is an uncontrolled wier and I have not put any gates in it.
US boundary is a Flow series, DS boundary is Normal depth.

I plan using a lateral flow series at the abstraction, immediately downstream of the weir (normally used for adding flow from small tributaries)
My question is, as it is an abstraction is it possible to specify the lateral flows as negative values with minus’ to essentially try to imitate an abstraction rather than an inflow?

Thanks in advance folks.

[Anonymous]

You should be able to enter a negative flow to remove water.

[JohnLonergan]

Yes, thanks.
I will try doing this today. I will post back to let you know if it is a success.

[Anonymous]

Ok. I tried this out and it does indeed work just fine.
Thanks.

[Anonymous]

hi. i am a student from Malaysia. im doing sediment transport analysis using hec-ras. i have a problem in entering data for quasi unsteady flow data. what is the difference between flow duration and computation increment in flow series? i really hope u can help me. thanks in advance.

[Anonymous]

There is a good description of the difference between the flow duration and the computation interval in sections 17-19 and 17-20 of the HEC-RAS 4.1 User’s Manual. Briefly, the flow duration is the amount of time that inflows are constant before changing to another value. Some streams may have relatively constant flows that persist for weeks or months during parts of the year, so the flow durations can be long to economize on flow data. The computation increment, however, might need to be shorter than the flow duration because the sediment transport, bed elevation changes and mixing of the bed material usually happen at a much shorter time scale than that at which the water flow changes. You might also look at HEC TD-13 for some background on how this split time step approach was developed.

[ctnuraina]

hye, i’m student from malaysia were do it a sediment project using hec-ras. i want to know about procedure. it ‘s do the input data for sediment first or input the flow data first?

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