This series of photos was helpful to this lay person, ER333. What exactly does “X linear” mean? And why is the 2039’ distance significant?
>>What exactly does “X linear” mean? <<
To identify an accurate location, or in this case, a linear distance “point” -measured from the start of the top of the main spillway chute - there are two linear reference distances that can be used. To keep the discussion “apples-to-apples” I used the same linear method as used in the blue line spillway plot in the second to the last image in Ray’s Post 1,735. Thus the intersecting point of interest on the blue line (spillway plot line) can be referenced using an a Linear X,Y coordinate system, but just using the X axis value. (btw- I find it extremely ironic that post 1,735 discusses a real and accurate measurement of 1,735ft - how about them odds...). Thus the “x marks the spot” is simply a vertical line (as greatly illustrated in Ray’s graphics).
The other linear reference, in full linear length, would be longer as it includes the curvature of the spillway. This second option would be equivalent to pulling a giant measuring tape down the spillway. In this case, the spillway curvature would make the length longer as it involves both the X and the Y together.
I was just trying to keep the discussion accurate in reference method, but simplified.
>>And why is the 2039’ distance significant?<<
Because this 2,039ft distance is well beyond (300ft+) the posited “inflection point” inference (1,735ft) of a causal mechanism in the context of a “failure or failure mechanism”. At the 2,039ft distance the spillway is in a linear slope - well beyond the curvature region. The extensive hydraulic flow studies of the spillway design was proven out well in advance.
side note: There are other complex factors to laminar waterflow verses a form of a “jump”. Fluid hydraulics in this spillway, while in a laminar flow state, will not separate. However, if there is any form of separation from a critically sharp bend, it would instantly convert into a damaging potential non-laminar flow.** The last thing a designer wants to occur is to create cavitation.
btw- A number of spillway models were live tested extensively in the lab before construction. Special piezoelectric sensors were extensively attached to the models to measure any pressure differentials in many different configurations, flow rates, and shapes. This was one engineering aspect that was very well done in the design of the Oroville spillway.
**There is one condition that occurs just before the “jump” into a violent non-laminar flow. It is a sharp pressure drop. The Pakistani’s learned this the hard way as their concrete slabs were “sucked away” up and outward from these sharp pressure drop differentials. Needless to say their dam failed (spillway). That is why the Oroville spillway construction design specifically shows “anchors” where the concrete slabs are anchored into the bedrock (10’ grid spacing on average).