Gates, weir and coulvert modelling of a Dam

[Anonymous]

Im my model I need to simulate the discharge from a surface spillway, bottom spillway and weir of a gravity dam.
I have already built a 2d flow area (dam downstream) a storage area(dam upstream) and a hydraulic connection (inline structure) between the 2.
However Hec-Ras allows only the following combinations for the inline structure:
Weir and gates
Weir and coulvert
I have already specified the first combination as well as the gate geometries but I am still missing the tunnel in the bottom of the dam. This tunnel starts 30 m upstream the Dam in the bottom of the lake and stops around 50 m downstream the dam in the river bed.

Any suggestion is appreciated

[Anonymous]

What version of RAS are you using?

Both inline structures inside of a 1D reach and a storage/2d connection between a 1D storage area and a 2D area, can have both gates and culverts.

So if the tunnel is uncontrolled you should be able to model it with a culvert. If the tunnel has a control structure on it, modeling the tunnel as a gate would probably be your best bet. A rectangular gate for a circular tunnel isn’t ideal, but can usually work. Or you can use a gate and then define your own gate rating curve vs water surface and gate opening.

[Anonymous]

I am using the version 5.0.3 of Ras.
Even if I could model coulverts, gates and weir togheter my worry is about the computational cell elevations downstream the dam. Actually if I model the tunnel as a gate, the gate invert will be at lower elevation than the computational cell bottom downstream becauqse the dam width. If I model the tunnel as a coulvert, i can set the coulvert length; in this latter case I don’t know which cell will be connected to the coulvert in the downstream side: the cell adjacent to the 2d hydraulic connection or the 2d flow area cell located at the same distance from the coulvert opening as the coulvert lenght.
Sorry but I am new in 2d modelling of hydraulic structures.
Thanks for your helpful suggestions.
D.

[Anonymous]

Version 5.0.3 will take the length of the culvert into account while computing the hydraulics. However, just like gates, the flow will be immediately adjacent cells. So for version 5.0.3, the cells on either side of the dam need to be big enough so that the edge of the cell makes it past the toe of the embankment and down into the channel.

For version 5.0.5, you can georeference gates and culverts and choose which cell(s) the inlet and outlet are in.

[Anonymous]

You were right…
I have installed the version 5.0.5 and actually coulvert modelling is quite easy ..since I knew the function Q(H,a) (a is the opening of the gate inside the tunnel), I am using the rating curve option, specifing the centerline coordinates of the tunnel. In this option however what really count are the inlet and outlet coordinates.

[Author]

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