Briones Inlet-Outlet Tower Seismic Retrofits

Orinda, California


East Bay Municipal Utility District

Briones Inlet/Outlet Tower is located approximately 750 feet upstream of the earth embankment dam that impounds Briones Reservoir. Briones Reservoir is one of the essential storage elements of East Bay Municipal Utility District’s water supply system. The tower, constructed in 1965, is used to feed water intermittently to the Orinda water treatment plant and used as an emergency backup reservoir. The tower is a 240-ft high freestanding, vertical, reinforced concrete structure with 60-inch butterfly valves at 7 levels operated by hydraulic lines from a platform at the top of the tower with an internal diameter that varies from 20 feet at the base to 10 ft at the top.

Seismic evaluations of the tower were conducted in 2008 and the tower was determined to be in need of retrofits as there may be potential for the tower to become damaged and inoperable following a large seismic event. In 2015, TERRA Engineers, Inc. was selected to perform the design of the seismic retrofit for the tower.

The scope of work includes site investigation, ground motion study, finite-element deformation analyses of various retrofit alternatives, ranking of alternatives, selection and final design report for a selected alternative, and production of construction documents, and design support during construction.

TERRA Engineers is also assisting the District staff with CEQA project descriptions and environmental permitting, including an USACE permit. TERRA has also been working closely with the District related to the proposed use of construction staging and laydown areas as portions of the site have potential for endangered species and wetland delineations that would impose restrictions on available land. Two biological surveys were conducted to identify environmental constraints (i.e., presence of rare plants, potential habitat for listed species, and features that would need to be avoided or protected during construction) and strategies were developed for documentation of habitat quality and avoidance measures. A cultural resources assessment is also currently underway.

Design is on-going and construction is anticipated to begin by 2020.