This image reveals a large 2foot diameter metal drain pipe buried under the footing elevation of the Emergency Spillway. This photo was taken before the flooding (overtop of the spillway). Notice the waterflow. A pipe of this size, and the angle it is projecting puts it underneath the ES Weir, would be unusual to drain the soil in the immediate vicinity (normal rainfall on the topsoil).
The Emergency Spillway blueprint design has the Weir as a concrete shell with aggregate fill. Drains are designed in the footing of the bottom of the aggregate horizontal to the elevation of the footing.
The blueprint design drawings indicate the Wier is sitting atop a rock foundation. But the type of rock may be what has been revealed in the deep cut erosion (hard rock but fractured or weathered rock).
What is also interesting is that this 2foot diameter drain is close to the opposite side of where the bubbles occurred. That drain pipe may have been a good indicator to any increased water underflow to the substructure of the ES Weir when flood levels occurred (just before and just after the cresting of the Weir).
Here is something of note - From the archives of the DWR Oroville Dam, page 93:
States the maximum probable flood has a probability recurrence in EXCESS of ten thousand years. (where both the Emergency Spillway and the Main Spillway would operate together - from high reservoir inflow).
Here is the latest view of this 2 foot diameter drain pipe. Pic taken while Emergency Spillway construction underway (rock spreading and concrete trucks at the ready).
Looks like the early stages of the emergency repairs before the rains moved in (sky is bright & overcast). Dumped rock, soil, and base weathered rock around CAT excavator look dry (not saturated, wet, or fresh rain soaked). Water is flowing from somewhere, albeit minor. Just more tidbits.
Underflow would threaten the main damn structure, right?
Underflow would threaten the main damn structure, right?
Is the draining water coming from ‘under’ the dam? Watch this:
Model Dam Fail