Water shut from Oroville Dam's damaged spillway in race against Mother Nature
The effort to protect Oroville Dam entered a critical phase Monday when engineers shut off water flowing out of the damaged main spillway, giving officials their first unobstructed view of the eroded concrete chute since a crisis prompted mass evacuations earlier this month.
For the next five to seven days, geologists and engineers will have an unhindered view of the concrete spillway, which on Monday was revealed to have severely deteriorated on its lower half during the last two weeks of use.
Repairs for the spillway are estimated in the hundreds of millions of dollars, and no timeline has been set for when they would be completed.
The main concrete spillway was damaged earlier this month after a week of powerful storms and after an earthen emergency spillway that was used when the reservoir reached capacity also rapidly eroded.
Officials need to keep the dam water levels in check because of damage to the emergency spillway that carries water when the reservoir goes above capacity. Damage to that spillway earlier this month prompted the evacuation of 100,000 people. Officials were able to use the damaged main spillway to reduce water levels, easing the crisis.
Interviews and records suggest that the near-catastrophe grew out of fundamental problems with the original design of the emergency spillway that were never corrected despite questions about its adequacy.