Hi janetjanet998, they armored the full basin at the road just behind the ES Weir spillway. There are no dark streaks or dark areas showing a water pooling or collection (to go to a "pipe"). If they were to place a pipe that allows water penetration from an Emergency Spillway Overflow, this penetration could be a weak point (pipe)- if it fails. Installing a pipe in the upstream road bank risks allowing an erosion flow underneath the shotcrete armoring, thus creating an erosion collapse via voiding under the armoring. This failure could defeat a large section of the armoring fairly quickly, leading to a "back head cutting" failure mode that caused the emergency evacuation of 188,000 people. A fully armored basin at the road will force waterflow to topple over the road, thus indirectly acting as an energy dissipator. note: I could be wrong, but if someone decided to insert a "failure" source into all of that expensive rock emplacement and shotcrete blanketing, someone should be "shotcreted"…
Note: (KC Burke) - the video shows the trucks creeping very very slowly, only one at a time & centered on the spillway bridge. Notice the other trucks are waiting for their turn to cross. That bridge has to have been enduring a significant load flexure repeated stressing from all of the heavy loads of rock, concrete trucks, etc during this whole crisis. This pic gave me a chance to point out (image) what I had mentioned upthread on the bridge.
That corrugated pipe could have been placed there under a condition as follows. There was a “wet area” that was not removed but was not dry when the gunite was placed and they placed a pipe as a “weep”.
Now, I would have just dug out the wet material, but the pipe obviously is there for some dang reason.