To: Honorable Mayor and Members of City Council
From: Phil Brun, Utilities Director
Prepared By: Addison LeBlanc, Assistant Engineer
TITLE:
Title
Conn Creek Spillway Alternatives Assessment
LABEL
RECOMMENDED ACTION:
Recommendation
Authorize the Utilities Director to execute a contract with GEI Consultants, Inc., in an amount not to exceed $290,480 for the Conn Creek Spillway Alternatives Assessment required by the California Division of Safety of Dams (DSOD), and determine this action is exempt from CEQA.
Body
DISCUSSION:
Conn Creek Dam was constructed in 1948 and had significant upgrades to the spillway in 1968. Since then, the City and DSOD have continued annual inspections and maintenance with no major upgrades. The City has been submitting engineering analyses and studies to DSOD, as part of the annual maintenance inspections which include recommendations that aid in reviewing the aging infrastructure. The hydrology analysis was reviewed in 1984 and the seismic analysis in 1992.
GEI performed the Spillway Condition Assessments required by the DSOD under the Spillway Re-evaluation program created in response to the 2017 Oroville Spillway incident. The assessments provided necessary interim repair recommendations in 2017, which were performed in 2019, and further investigations in 2020 for repairs planned for July 2022.
The Spillway Re-evaluation program includes updates to the hydrologic and hydraulic analysis of the spillway as part of the long-term planning. Recent updates to the hydrology reports that are used to analyze the hydraulic capacity of the Spillway were included in an amended report and submitted to DSOD for review of the probable max flood (PMF). DSOD's review confirmed the report's findings that the spillway capacity needs to be increased to meet current design standards. DSOD requested the analysis be further refined with feasibility and alternatives analysis to meet modern design standards and address the deficiency.
The plan...
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