HEC-RAS Boundary condition

[sam1]

I am a new user of HEC-RAS, I have a simple question considering the boundary conditions.

I have a simple application of a 2D flow zone with an upstream boundary condition as a flow hydrograph.

Is it necessary for the condition at the Downstream BC to be anormal depth? Or it can be a flow hydrograph with a negative flow value to be considered as a outflow (flow going out of the flow area).

And if it can be a flow graph, will HEC-RAS use the downstream boundary hydrograph to calibrate the model and calculate a simulated flow fairly close to the downstream boundary hydrograph?

[Anonymous]

Since no one has answered you still i will again reiterate, that yes it is possible. As youve stated it is in the manual as an acceptable boundary condition. However, ive never seen anyone, firm, reviewer, client accept this type of DS BC. I would do numerous test models before i ever implicated a DS BC like that in my model. For example i would first run a 2D area with no inflow, only the DS negative value flow hydrograph and just review what happens. Then i would put a constant inflow over time for a set simulation and see what the DS BC pulls out and check if it makes sense; if needed calculate by hand what results should be expected and what occurred.

[Author]

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