Engineers are racing to limit erosion damage to the stricken Oroville Dam in California before more storms hit the area.
After evaluating a hole caused by erosion on Oroville Dam’s auxiliary – emergency – spillway yesterday afternoon, engineers filled it with large rocks and gravel using trucks and helicopters.
Water stopped flowing down the auxiliary spillway, which acts as a passage for surplus water, after the lake level dropped to 272m yesterday – slightly lower than the 275m above sea level limit breached on Saturday morning (11 February).
However, a high volume of water continues to crash down the dam’s primary spillway – which has also suffered erosion damage – at 2,831m³/s.
Engineers are monitoring both spillways for signs of further damage. The race to repair the erosion is on as the next storm is expected to begin late Wednesday night (15 February), adding pressure while water levels at the reservoir remain high.
Heavy rain from unusually severe storms led to erosion damage on the primary spillway’s concrete chute on 7 February. Officials closed the structure before gradually reopening the spillway with controlled water flows.
However, rising water levels in the reservoir led to water flowing down the auxiliary spillway for the first time in the dam’s 48-year history. On Sunday (12 February) it also developed signs of erosion, this time at its head.
Concerns about the resulting high volumes of water downstream of the dam resulted in an evacuation order being issued to 180,000 residents.