After more than 188,000 people evacuated from central California towns north of Sacramento, crews at Oroville Dam on Feb. 13 scrambled to fill erosion that developed hours after an emergency spillway was put into service for the first time in the dam’s 50-year history. The previous day,water started to pour over the 1,700-ft-long weir onto a wooded hillside and into the Feather River after erosion on the concrete-lined main spillway forced operators to cut back flow to 55,000 cu ft per second. The 40-ft sinkhole on the controlled waterway came on the heels of a series of storms that filled the reservoir close to its 901-ft capacity. After operators discovered damage to the alternate spillway, they increased main spillway flows to 100,000 cfs, despite the damage. By Feb. 13, the water level dropped below the top of the emergency spillway. California Dept. of Water Resources Acting Director Bill Croyle said the main-spillway damage seemed to be stabilized and the higher flows continued, as he hoped to reduce the water level by 50 ft in advance of a new storm, expected to arrive the night of Feb. 15. During that dry window, helicopters dropped bags of rocks onto the earthen wall’s damaged areas, and trucks carted slurry to the site in an attempt to stabilize the slope. With a crest height of 770 ft and a reservoir capacity of 3.5 million acre-ft, the 1968-era dam is the tallest earthen dam in the world and the centerpiece of the California Water Project.
Oroville Dam Spillway Repaired in Advance of New Storm
February 15, 2017