Nevada Irrigation District (NID) has carried out underwater maintenance at French Dam in California, US, replacing hydraulic equipment that had been operating for almost 90 years.
Commercial divers were deployed at French Lake this summer to work on the low-level outlet gate at French Dam, which is NID’s oldest dam still in operation.
Located on Canyon Creek in the South Yuba watershed at an elevation of approximately 6660ft (2030m), French Dam was originally constructed in 1858-1859 and later raised in 1948. The reservoir has a storage capacity of nearly 14,000 acre-feet.
The low-level outlet gate dates from 1937, while its underwater hydraulic actuator, which controls the opening and closing of the gate, had remained in service for 89 years.
NID said the actuator and associated hydraulic lines had become worn and developed leaks over time, making operation of the gate increasingly difficult. Operating the equipment had come to require around 200 manual pumping strokes.
As part of the maintenance programme, a commercial dive crew removed the ageing hydraulic ram from beneath the reservoir surface. This allowed its dimensions to be measured accurately so that a replacement actuator could be fabricated.
The project also included replacement of deteriorating hydraulic lines to restore reliable operation of the low-level outlet gate.
The outlet is used to manage releases from French Lake and forms part of the infrastructure required for the safe operation of the reservoir. NID project documents had identified the ageing hydraulic lines, pump and ram as requiring replacement to ensure the outlet could continue to be operated safely and effectively.
The work forms part of NID’s wider programme to maintain and modernise its water infrastructure, which includes facilities dating from California’s Gold Rush era alongside more recent treatment, monitoring and control systems.
French Dam has now been in operation for more than 165 years, while the outlet equipment addressed by the latest project had been operating since the 1930s.
