THE GEOLOGY AND ONGOING REPAIRS OF THE AGING CALIFORNIA AQUEDUCT IN THE CENTRAL VALLEY

One of the major water conveyance systems through the Central Valley, the State Water Project's California Aqueduct, is an open canal that conveys about 1,500 gallons per minute every day to central and southern California. The California Aqueduct was built in the late 1960s and is approaching 50 years of age. The effects of that aging are evident as seeps, sinkholes, dribbles, depressions, leaks, and occasionally, major leaks. The underlying geology almost always plays a role in the problems manifest at the surface. Regional subsidence and locally poorly-consolidated to unconsolidated sedimentary debris flow deposits were recognized during the design phase of the California Aqueduct. Settlement ponds were constructed to consolidate the sediments and promote hydrocompaction. Shortly thereafter, the California Aqueduct embankments and other appurtenant structures were built. Since that time, a variety of problems have been encountered, including a few major leaks that required urgent repairs. These repairs nearly always must be completed without taking the California Aqueduct out of service, which would disrupt and potentially cause significant damages to agricultural, industrial, commercial, and residential users. This leads to a variety of repair alternatives, with no one-size-fits-all repair. Remedial repairs that have been used include excavating and re-compacting the embankment, injecting bentonite, compaction grouting, installing interlocking steel sheet piles, underwater grouting through the liner, permeation grouting, and re-lining the Aqueduct with an impermeable liner. This presentation will discuss a few of these canal repairs and how they relate to the underlying geology.