Measurement Method – diversions over 100 AF/year have to be certified by a qualified professional, although the deadlines for 100 to 1,000 AF diversions are July 1/October 1. You can build it but it has to be certified.
Alternative Compliance Plan – if your device does not comply, or standard devices will not work, but you have a reasonable measurement plan, fill this out. It will be posted online by the Water Board, and they do not approve or evaluate it. If nobody (state or federal agency, group, or individual) complains to the Water Board, you’re done. If the Water Board says it’s not good enough, you may have as few as 30 days to put in a compliant measurement device to avoid fines.
Supplemental Statements Of Diversion And Use for Water Rights Under Applications, Permits, and Licenses.
What Device Can You Put In Quickly, if Your Diversion Is Over 1,000 AF/Year?
A temporary weir can be put in fast – as little as half a day. You should be able to say it’ll last a couple of years. It needs to be sealed up with plastic and/or dirt so it does not leak through or around.
Whatever you do, it has to be certified…but by whom? According to http://www.waterboards.ca.gov/waterrights/water_issues/programs/diversion_use/docs/meas_method_instruct.pdf, it can be: “…A) A California-registered Professional Engineer; or B) A California-licensed contractor authorized by the State License Board for C-57 well drilling or C-61 Limited Specialty/D-21 Machinery and Pumps; or C) A person under the supervision of a California-registered Professional Engineer and employed to install, operate, and maintain water measurement and reporting devices or methods; or D) In the case of a right or a claimed right to divert by an agency of the federal government, a hydrologist or professional engineer experienced and trained in water measurement who is employed by the federal agency in that capacity….”
The ideal weir, whether suppressed or contracted, needs 2′ available depth upstream and downstream of the weir boards. That’s enough for an (ideally) 1.5′ high weir, plus 0.45′ static head on top of the weir boards. The water downstream needs to be at least 0.25′, or 3″ below the top of the weir boards to have a good nappe (air gap between the boards and falling water).
The 0.45′ static head gives 1 cfs per foot of length of weir. You can go higher with the special Kindsvater-Carter equations – you’ll use those to develop a rating curve. You can drop the weir boards down a little, but not so much you drown out (submerge) the weir. So, ideal parameters can be stretched some if you take great care to use the correct calculations.
When it comes right down to it, 2 braced T-posts, or 2 lengths of galvanized pipe, with boards and plastic could be certified as compliant for a year.
I have done that in a pinch when I was a bureaucrat Watermaster. The important things are the heights and depths.
One more possibility – use an orifice in your weir box, but you would have to have 2 data collectors per measurement device. An orifice can have as little as 0.2′, or 2.4 inches of head difference between upstream and downstream; more head is better for accuracy. If the ditch is really flat, use a weir setup that has exposed weir boards down to the sill of the device, so you can cut a hole in a lower board for your orifice.