What Is the Lake Berryessa Glory Hole
The Lake Berryessa glory hole is the morning glory spillway at Monticello Dam in Napa County, California. It is a controlled overflow structure designed to release excess water from Lake Berryessa into Putah Creek when the reservoir reaches full capacity. The concrete funnel-shaped inlet is one of the most recognized spillway designs in the United States.
The structure is operated by the Solano Irrigation District and the U.S. Bureau of Reclamation as part of the Solano Project. It regulates water levels for agricultural irrigation, municipal supply, and downstream flood control. The spillway activates only when the lake surface elevation reaches approximately 440 feet above sea level.
Design Specifications and Capacity
The morning glory inlet has a diameter of about 72 feet, making it one of the largest funnel spillways in the world. The concrete tunnel extends roughly 200 feet before transitioning into a straight discharge conduit that releases water into a stilling basin downstream.
The spillway can discharge up to 48,000 cubic feet per second when fully operational. This capacity allows the system to handle significant inflow events during heavy storms. The design was completed in the early 1950s, and the dam and spillway became fully operational in 1957.
Operational History and Recent Activity
The Lake Berryessa glory hole has been activated sporadically since its completion, typically during periods of heavy winter rainfall or snowmelt runoff. Notable full activations occurred during major storm events in the 1980s, 1990s, and 2010s. Each activation draws significant public attention due to the dramatic visual of water swirling into the funnel.
Recent hydrological data from the U.S. Bureau of Reclamation and California Department of Water Resources show that the spillway remains a critical component of flood risk management in the Putah Creek watershed. The system is inspected regularly to ensure structural integrity and operational readiness.
Related Infrastructure and Water Management
The Solano Project includes Monticello Dam, Lake Berryessa, and associated diversion facilities that supply water to farms and communities in Solano County. The project is managed in coordination with state and federal water agencies to balance supply, demand, and environmental flows.
Flood Control and Reservoir Operations
During high-water events, operators monitor lake levels closely and coordinate releases through the glory hole and other outlet works. These operations follow protocols set by the Bureau of Reclamation and align with broader California water management plans.