Storage areas as DS boundary for un-steady flow calculations?

[Marulke]

The RAS user guide states that storage areas may be used at the downstream or upstream end of a reach.

In all simulations you will need to specify boundary conditions at the DS and (maybe) the US end.

This is not a problem when running a steady flow simulation. There are several options for DS boundary condition at the storage area, for example a rating curve.

However, if I have a storage area at the downstream end and want to specify unsteady flow data, the only boundary conditions options for the downstream storage are are “lateral inflow hydrograph” and “Groundwater inflow”. Not useful as DS boundary. I need to specify the water level as function of time or flow.

Question:
Is it possible to use a storage area at the downstream end of a reach for un-steady flow simulations?
How do you apply some stage discharge relationship as DS boundary

[Chris G.]

What I’ve done in the past is just downstream of the downstream storage area, I put a “dummy” reach with 2 cross sections. Put them very close together, but similar in size to the reservoir. Then add your downstream stage hydrograph to the downstream cross section of the dummy reach.

Chris G.

[Author]

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