Aerial photo of Lopez Lake Dam & spillway.
Aerial photo of Lopez Lake Dam & spillway.

Spillway Condition Assessments for Lopez and Whale Rock Dams

Author: Public Works
Date: Monday, July 31, 2017 12:00 AM

The California Department of Water Resources has directed a detailed condition assessment of spillways at over 93 dams in California.


The spillways at Lopez Dam, near Arroyo Grande, and Whale Rock Dam, in Cayucos, are included in the State’s directive. Staff at the County, responsible for Lopez Dam, and the City, responsible for Whale Rock Dam, are moving expeditiously forward to complete these assessments. Although neither spillway exhibits any of the conditions that early reports indicate may have led to the failure at Oroville, both the County and City are closely following the information developed out of the Oroville assessment. Maintaining public safety at these facilities is our top concern and we are committed to preparing assessments that meet the highest standards of engineering analysis.

Also, in June of this year, the legislature passed and the Governor signed Senate Bill (SB) 92. SB 92 requires the preparation and State review of a “dam failure inundation map” and Emergency Action Plan for “high and extremely high hazard” dams in California. This designation is based solely on the impacts that an uncontrolled release of water would have on the downstream community, not the actual condition of the dam and spillway. Both Lopez and Whale Rock dams are in this category, however, both dams already have published inundation maps and Emergency Action Plans. SB 92 will provide a process whereby both the Department of Water Resources and the State Office of Emergency Services will review the maps to ensure adequacy.

As more information becomes available, both the County and the City will keep the community fully informed.