Two things I learned on the farm decades ago.
1. Drains should be lower than the area you are addressing. IE, they should of been placed in their own “trench”. No danger of the water having to go up to exit and no thinning of the slab.
2. You don’t use round “river rock” to keep a buried object in place - especially on a slope with a concrete pour over it.
And I am not a civil engineer, just a lowly mechanical engineer.
You are very well correct. Indications are is that the designers were hesitant to carve and then seal capture drain basin “grooves” in the foundation rock. In addition, the bedrock would have to have been sealed to resist/prevent water penetration into the bedrock until it reached the catch drain basin grooves.
Stagnation Pressure Failures of spillways weren’t well documented in the day. Only after 2 dams failed did this issue become a high consideration. However, Oroville was already completed. Then the issue became a discussion on if the anchoring system + crack/seam maintenance repairs would suffice. If not, the cost would be very painful to tear up and replace this (now proven) fatal design.
Engineering judgement in compromises or analysis has led to failures of great magnitude. In the case of a dam, with the destruction and damage it would incur to the State of California, businesses, agriculture, citizens, and even the federal government in bailing it out, the Engineering judgement MUST be such there are very high safety factors and redundancies.
What is worse, competent engineers knew the warning signs and should have raised the alarms years back. Instead, we are witnessing one of the greatest engineering failures in history. No excuses.
btw- good engineers are in all lines of work. I’ve known engineers that were just as good if not better in analysis of designs in cross engineering fields. In fact, a top Weyerhaeuser research PhD who was fearless. He had his degree in mechanical engineering, but was able to apply his skillset in many other fields. He also relied on talking to knowledgeable people to get their input. A fantastic person. Working with classified scientists & engineers, they too rely on sharing expertise. There needs to be more “grey beards” to pass on these characteristics to all so that the wealth of skill, drive, responsibility, and knowledge is given to those that are willing to grow and learn.