Practical Ramp Flume Design

[debgallery]

Any flume experts out there? I'm using WinFlume for the first time to design a ramp flume for an irrigation ditch intake. I'd be very grateful for some peer review of my design (see attached WinFlume file and output pdf's).

The existing ditch is between 3'-4' wide at the bottom, approximately 5' deep with 0.5:1 side slopes. It's fairly straight for a good stretch and diverts water directly from a major river. I have a detailed survey with cross-sections and have used HEC-RAS to estimate that it can carry flows up to about 80-cfs. The water right on this ditch is 8.5-cfs so the measuring device needs to be accurate at that flow. I've chosen a ramp flume because the ditch is pretty flat.

I entered the data into WinFlume and modeled the approach and tailwater sections after the actual dimensions of the ditch while playing with the control section to make the design "acceptable". I also used the "auto adjust lengths" button, which is why the lengths have so many sig. digits.

How does the initial design strike you? Does it seem reasonable? I'm assuming I should play with the dimensions to make them more practical for construction. I assumed the material would be metal but would a concrete structure be more practical?

Any advice or comments are welcome. Thanks.

 

[bimr]

There are a number of firms that make prefabricated flumes from FRP material. The flumes have standard dimensions for measuring flow. These FRP flumes are then set into the formwork prior to installation of concrete for the structure.

It is preferable to use a prefabricated flume because it is very difficult for a contractor to get the dimensions accurate enough in the field.

 

[cvg]

how will you control flow? assume you will need either a slide gate or flume gate. you can easily measure flow at either one without needing another in-line flume.

 

[debgallery]

Thanks for your responses. I talked with a manufacturer who said that they used to make pre-fab flumes larger than the 20-cfs size but found that they were having to encase them in concrete anyway so now they recommend a custom concrete flume for anything that large. For this case I've actually decided to go with a 10-cfs flume since the water right is only 8.5-cfs and there's no need to measure higher flows. We're going to control the flow with a canal gate at the point of diversion from the river. The Colorodo Department of Water Resources is requiring that we have a more accurate measuring device than just a gate. Thanks again for your input.