Page - 42 - in Book of Full Papers - Symposium Hydro Engineering

OROVILLE DAM SPILLWAY INCIDENT — SITUATION DEVELOPMENT, INCIDENT RESPONSE AND PUBLIC SAFETY William Croyle Acting Director (Retired), State of California, Department of Water Resources David Gutierrez Technical Advisor, GEI Consultants, Inc. Joel Ledesma Assistant Division Chief, Operations and Maintenance, State of California, Department of Water Resources Sharon Tapia Chief, Division of Safety of Dams, State of California, Department of Water Resources Frank L Blackett Regional Engineer, Federal Energy Regulatory Commission UNITED STATES OF AMERICA 1. INTRODUCTION Oroville Dam is located on the Feather River in northern California (USA). At 234.7 m (770-ft) tall, this earth embankment is the tallest dam in the United States. With its 4.3 billion m3 (3.5 million acre-feet) of storage, Lake Oroville is the second largest reservoir in California, supplying water to cities as far south as Los Angeles. The Oroville Dam, reservoir (Lake Oroville), and hydropower plant facility is the flagship of the State Water Project (SWP), which is owned and operated by the State of California, Department of Water Resources (DWR). The 2016-2017 Winter Storms brought record breaking precipitation to the Northern California Sierra mountains including the Feather River watershed. On February 7, 2017, the Oroville Dam’s 54.5 m (179-ft) wide Flood Control Outlet (FCO) Spillway chute (Fig. 1) was releasing water to control the Lake Oroville reservoir level in accordance with the prescribed operations plan. During this operation, the FCO spillway suffered a catastrophic failure of the lower chute area eventually resulting in the loss of approximately 427 m (1400 ft) of the lower chute, including the scour of more than 1.2 million m3 (1.6 million yd3 of soil and rock materials. On February 11, 2017, the Emergency Spillway (Fig. 1) was used for the first time since the project was completed in 1968. During this operation, significant erosion and scour caused by the Emergency Spillway overflow led authorities to fear for the safety of the spillway structures, resulting in the activation of the Emergency Action Plan and evacuation of about 188,000 persons from downstream communities. 42