Cachuma Reservoir


The United States Bureau of Reclamation (USBR) constructed Lake Cachuma and Bradbury Dam in the early 1950s as part of the Cachuma Project. The construction of Bradbury Dam began in August of 1950 and was completed on June 17, 1953. Filling of the reservoir was completed in 1958. The principal features of the Cachuma Project are Bradbury Dam, Lake Cachuma, Tecolote Tunnel, the South Coast Conduit and distribution systems. Included in the main conduit system are four regulating reservoirs and the Sheffield Tunnel. Tecolote Tunnel was one of the most difficult tunnel projects undertaken by the USBR. The tunnel was completed in 1956 following a difficult six year construction period. Tunnel construction was hampered by groundwater inflow reaching 9,000 gallons per minute, temperatures up to 117o F, and dangerous levels of methane gas. Visit the City of Santa Barbara's website for more information on the Cachuma Project.

Costs to Excavate Cachuma
Frequently the question comes up about excavating Cachuma Reservoir while the Lake is low as a way to increase storage and water supplies. While this sounds like a good idea, in reality the costs of such a move makes little sense.  To quantify the costs it is best to put the project into perspective in terms of overall costs, and costs per acre-foot.

Cachuma functions as a true reservoir and as such the volume of the lake is not utilized in a single year, but rather stores water in wet years to last through a critical drought period.  As such, the excavation of materials must be allocated over the drought period.  For Cachuma, that requires about a 10-1 ratio of volume excavated to yield provided.  This accounts for evaporation and other losses in the reservoir.

So for ease of calculation, we will assume that we desire to get 1,000 acre-feet of yield out of Cachuma. Thus we need to excavate 10,000 acre-feet of new volume.  The cost breakdown is as follows:
10,000 acre-feet equals 16.1 million cubic yards.
At $10 per cubic yard (conservatively low) that renders an excavation cost of $161 million.
Adding in environmental, permitting, engineering, and construction management (25%), that leaves us at about $200 million.

NET PER ACRE FOOT COSTS = $200,000 per acre-foot

Technical issues with the project could easily increase these costs several fold.  First, it needs to be recognized that one cannot dig a 10,000 acre-foot hold in the lake.  The sedimentation is spread out over the lake bottom so in effect one must either skim this material over 100's of acres, or a localized excavation that can ensure connection to the lake (not stranding this volume) that still covers a sizable area.

The material needs to be trucked, or a location found close to place the excavated material that ensures it does not re-enter the lake.  In calculating the costs, there was no allowance for property acquisition either, so as such the costs of this work could be significantly higher.

Conclusions:  At a cost of over $200,000 per acre-foot, many other options for water supply are more economic and less environmentally damaging.  


Bradbury Dam and Cachuma Reservoir