Understood. I was specifically referring to the test designs, on the flow model bed, where there were variations of wings or funnel shapes just after the spillway gates. The hump has always bothered since the first time I stood at the base and looked up the spillway in 1982. Very few if any dams in the US have a spillway that long. Extra care should of been exercised in the design.
They appear to be slowly throttling back the flow:
http://cdec.water.ca.gov/cgi-progs/queryF?ORO
Hopefully, tomorrow we will be able to see
the upper portion of the spillway held in place,
and the debris in the river is minimal.
(fingers crossed)
Now I understand your point. The upper throat has the appearance of some Venturi features.
I am curious how local and distant communities draw water from the lake. Is it only from the Feather itself?