modeling dams

[Nikolabg]

I have an complex concrete dam (small hydroelectric plant) on a river with a weir, 3 gated spillways and circular culvert for low flows.

1. What is the best way to model that culvert? If i model dam as inline structure i only have options to model weirs and gated spillways, no culvert option?

2. Weir, gated spillways and culvert ends with energy dissipators (USBR type 3 for weir and spillways and CSU Rigid Boundary Basin for culvert). What is the best way to model them? Where to put CS’s which will define them considering i have mandatory 2 CS downstream of the dam which define inline structure.

3. IS HEC RAS really a good tool for modeling complex dams with stilling basins?

THX

[Marulke]

1 Culvert
If the culvert has inlet control the capacity will only depend on the headwater. You can compute the capacity curve, Q = f(H), and enter it as a user defined gate curve in the Inline gate editor. (I haven’t tried it, just guessing.)

2 Stilling basins
Why do you want to model them? The design is already given in handbooks. You may need to model the approach flow to find the flow depth and velocity at the entrance to the stilling basin.

The tailwater level is also important, but is normally controlled from downstream (sub-critical DS reach), and can be modeled with RAS.

Flow inside the dissipators can not be properly modeled with HEC-RAS, but you don’t need it. However, it is convenient to include some simple representation of the basins so you get a continuous model.

3 Good tool?
RAS is easy to use and gives the main parameters you need for detailed design (velocity, depth). Using 3 D models is much more involved and may still not yield good results inside stilling basins, under gates etc.

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