Until spec numbers are translated into a visual scenario, people tend to overlook the magnitude of a lurking problem. The new "concept design" is a disaster in waiting if applied to BOC's required specifications. Yet, DWR is not speaking of the hillside damage contingency/issue (i.e. why is armoring not placed for the full hillside?). Have you seen the concept drawing? Note that there is a specific boundary transition to -> "soil".
In engineering, specifications are everything. However, if Chief Engineers & DWR's management do not communicate the true significance of what the specification(s) really mean, verses their "concept design", they could be stated to be "less than forthcoming". (they need to explain this to the public).
The image of the significant hydraulic turbulence down the hillside is exactly what will happen in the BOC specified design flow of 369,000 cfs from the new emergency spillway. The MAJOR disconnect in what is being presented in aesthetic concept pictures of the RCC buttress & a mini-apron design is "what is going to happen to the rest of the 90% of the severely erodible hillside?". DWR has not addressed this scenario of the massive erosion failure mode (i.e. haven't pointed out that the mini-apron does not address a full apron hillside secure design - that a one-time use of the spec flow of the ES will recreate another risk of a main dam failure, via back flow eddy swirl toe erosion).
= = From post 2,675 (link below)
The New "Board of Consultants (BOC)", of advising experts to DWR, has stated a requirement of restoration of the rated 646,000 cfs flood capacity of the combined spillway flows (see March 10, 2017 report below). HOWEVER, the new "upped" rating of a huge 396,000 cfs requirement of a new Emergency Spillway includes the caveat: "damage below the Emergency Spillway to be expected". This directly implies that there will be erosive damage. Given the known geology and the actual alarming erosion of "rotten rock" & debris from the last Emergency Spillway incident, the only method to prevent a repeat of this is to armor the hillside all of the way to the Feather River.
We will see how this "damage to be expected" is translated into a new design. Is the "damage" limited to the "armoring itself" or is it damage to an unconsolidated hillside further below an "armoring apron" (or both)? The latter is what could engender a very problematic sequence. (1) If the max rated 396,000 cfs destroys the hillside, a "dam" would form in the Feather River channel. (2) The main spillway chute is upstream, thus flows from the main spillway likely would "backflow" towards the "toe" of the earthen dam. (3) This backflow would form an "eddy swirl" at the "toe" terminus. (4) dangerous destabilizing erosion of the backside toe of the earthen dam would occur. (5) to prevent this "eddy swirl" or partially limit its intensity, the main spillway would need to be slowed or shut off. (6) Further erosion would occur from the Emergency Spillway handling "flood control". This is an inverse repeat of what is currently going on at the dam - BUT- with the exception of a lesser eddy back flow towards the dam (has since been mitigated by the excavation of most of the 1.7 million cubic yards of rock/debris).
The only clean design that "preserves the safety of redundancy" is by fully armoring the Emergency Spillway for the full length of the hillside to the Feather River. But the associated costs for this may become a difficult "political" funding issue.
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Thanks EarthResearcher333. Keep up the good work.
Dang man, what would happen if you published an “exposé” book on all of this? An exposé by someone with enough technical knowledge to withstand the critics. The best weapon here looks like it would be widespread public awareness that would put pressure on any corruption and hopefully usher in good-faith officials with analysis and remedies that could, if not save money, at least save lives.