Calaveras Reservoir
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Calaveras Reservoir is located primarily in
Santa Clara County, California Santa Clara County, officially the County of Santa Clara, is the sixth-most populous county in the U.S. state of California, with a population of 1,936,259, as of the 2020 United States Census, 2020 census. Santa Clara County and neighboring Sa ...
, with a small portion and its dam in
Alameda County, California Alameda County ( ) is a county located in the U.S. state of California. As of the 2020 census, the population was 1,682,353, making it the 7th-most populous county in the state and 21st most populous nationally. The county seat is Oakland. Al ...
. In Spanish, Calaveras means "skulls". The reservoir is fed mainly by Arroyo Hondo and Calaveras Creek. Lying in the
Calaveras Valley Calaveras Valley is a valley east of Milpitas, California in the San Francisco Bay Area. It has formed primarily as a result of the actions of the Calaveras Fault. The southern end of the Calaveras Valley is a few miles south of Calaveras Reservoir ...
, the region is geologically active with the
Calaveras Fault The Calaveras Fault is a major branch of the San Andreas Fault System that is located in northern California in the San Francisco Bay Area. Activity on the different segments of the fault includes moderate and large earthquakes as well as aseismi ...
parallel to and to the west of the dam site. The seismic hazard forced replacement of the original dam. The replacement dam began construction in 2011 and was completed in 2019. The
Calaveras Valley Calaveras Valley is a valley east of Milpitas, California in the San Francisco Bay Area. It has formed primarily as a result of the actions of the Calaveras Fault. The southern end of the Calaveras Valley is a few miles south of Calaveras Reservoir ...
has diverse wildlife including
deer Deer or true deer are hoofed ruminant mammals forming the family Cervidae. The two main groups of deer are the Cervinae, including the muntjac, the elk (wapiti), the red deer, and the fallow deer; and the Capreolinae, including the reindeer ...
,
coyote The coyote (''Canis latrans'') is a species of canis, canine native to North America. It is smaller than its close relative, the wolf, and slightly smaller than the closely related eastern wolf and red wolf. It fills much of the same ecologica ...
s, squirrels,
turkey vulture The turkey vulture (''Cathartes aura'') is the most widespread of the New World vultures. One of three species in the genus ''Cathartes'' of the family Cathartidae, the turkey vulture ranges from southern Canada to the southernmost tip of South ...
s,
red-winged blackbird The red-winged blackbird (''Agelaius phoeniceus'') is a passerine bird of the family Icteridae found in most of North America and much of Central America. It breeds from Alaska and Newfoundland south to Florida, the Gulf of Mexico, Mexico, and ...
s,
yellow-billed magpie The yellow-billed magpie ''(Pica nuttalli)'', also known as the California magpie, is a large bird in the crow family that is restricted to the U.S. state of California. It inhabits the Central Valley and the adjacent chaparral foothills and m ...
s,
red-tailed hawk The red-tailed hawk (''Buteo jamaicensis'') is a bird of prey that breeds throughout most of North America, from the interior of Alaska and northern Canada to as far south as Panama and the West Indies. It is one of the most common members with ...
s,
brewer's blackbird Brewer's blackbird (''Euphagus cyanocephalus'') is a medium-sized New World blackbird. It is named after the ornithologist Thomas Mayo Brewer. Description Adult males have black Feather, plumage with an iridescent purple head and neck and glo ...
s,
purple martin The purple martin (''Progne subis'') is a passerine bird in the swallow family Hirundinidae. It is the largest swallow in North America. Despite its name, the purple martin is not truly purple. The dark blackish-blue feathers have an iridescent s ...
s,
barn swallow The barn swallow (''Hirundo rustica'') is the most widespread species of swallow in the world. In fact, it appears to have the largest natural distribution of any of the world's passerines, ranging over 251 million square kilometres globally. ...
s,
bullock's oriole Bullock's oriole (''Icterus bullockii'') is a small New World blackbird. At one time, this species and the Baltimore oriole were considered to be a single species, the northern oriole. This bird is named after William Bullock, an English amateur ...
s, and
warbler Various Passeriformes (perching birds) are commonly referred to as warblers. They are not necessarily closely related to one another, but share some characteristics, such as being fairly small, vocal, and insectivorous. Sylvioid warblers Th ...
s. Since at least 2008, a pair of
bald eagle The bald eagle (''Haliaeetus leucocephalus'') is a bird of prey found in North America. A sea eagle, it has two known subspecies and forms a species pair with the white-tailed eagle (''Haliaeetus albicilla''), which occupies the same niche as ...
s has nested regularly.


History

In the 19th century, the Calaveras Valley which the reservoir now fills was primarily an agricultural region known for its production of
hay Hay is grass, legumes, or other herbaceous plants that have been cut and dried to be stored for use as animal fodder, either for large grazing animals raised as livestock, such as cattle, horses, goats, and sheep, or for smaller domesticat ...
,
strawberries The garden strawberry (or simply strawberry; ''Fragaria × ananassa'') is a widely grown hybrid species of the genus '' Fragaria'', collectively known as the strawberries, which are cultivated worldwide for their fruit. The fruit is widely ap ...
, and tomatoes. Because of San Francisco's increasing demand for drinking water at the turn of the 20th century, the farmers in the region were forced to sell their land to the
Spring Valley Water Company The San Francisco Public Utilities Commission (SFPUC) is a public agency of the City and County of San Francisco that provides water, wastewater, and electric power services to the city and an additional 1.9 million customers within three San Franc ...
, which in turn sold it to the San Francisco Water Company. The first dam on the site, built in 1913 by the
Spring Valley Water Company The San Francisco Public Utilities Commission (SFPUC) is a public agency of the City and County of San Francisco that provides water, wastewater, and electric power services to the city and an additional 1.9 million customers within three San Franc ...
, rapidly changed the sensitive hydrology and natural environment of the Calaveras Valley. That dam suffered a collapse of the upstream slope in 1918 due to design and material flaws. Its replacement, which stood until 2019, was the largest
earth-fill dam An embankment dam is a large artificial dam. It is typically created by the placement and compaction of a complex semi-plastic mound of various compositions of soil or rock. It has a semi-pervious waterproof natural covering for its surface and ...
in the world when completed in 1925. It was 245 feet high, with a length of 1200 feet at its crest. The city and county of San Francisco owns and operates the dam and reservoir for municipal water supply. Due to concerns about its seismic rating, the 1925 dam was replaced by a new dam constructed just downstream from 2014 to 2019. The reservoir is reported to contain a large population of largemouth bass, rainbow trout and other species. However, fishing is prohibited. The
San Francisco Public Utilities Commission The San Francisco Public Utilities Commission (SFPUC) is a public agency of the City and County of San Francisco that provides water, wastewater, and electric power services to the city and an additional 1.9 million customers within three San Franc ...
(SFPUC) owns 36,000 acres (150 km2) in the Alameda Creek Watershed. Some lands in the watershed are leased to livestock companies for cattle
ranching A ranch (from es, rancho/Mexican Spanish) is an area of land, including various structures, given primarily to ranching, the practice of raising grazing livestock such as cattle and sheep. It is a subtype of a farm. These terms are most often ...
to control vegetation and prevent fires. Most of the land is closed to the public because of concerns over drinking water safety and quality.


Dam replacement

The dam site has an active earthquake fault nearby, and the original 1925 dam was seismically vulnerable. If the dam had collapsed when full, it would have flooded parts of
Fremont, California Fremont is a city in Alameda County, California, United States. Located in the East Bay region of the San Francisco Bay Area, Bay Area, Fremont has a population of 230,504 as of 2020, making it the fourth List of cities and towns in the San Fra ...
with a wall of water high. Dam regulators for the state of California restricted the capacity of the original dam in 2001, to mitigate the seismic threat. The capacity of the original dam was limited to about one-third of the nominal 100,000 acre-feet (120 million cubic meters). To restore lost capacity, the San Francisco Public Utilities Commission constructed a replacement dam located downstream from the original 1925 dam. The dam replacement took twice as long (eight years instead of four years) and cost twice as much as originally scheduled. Hazardous geological conditions were discovered near the proposed west abutment in 2012 and near the proposed spillway. The dam site was weakened by at least two ancient landslides. When construction started in 2011, the budget was $420 million, and completion was expected in 2015. The seismic redesign required three million additional cubic yards (two million cubic meters) of excavation, far more than the original seven million cubic yards (five million cubic meters). The spillway had to be relocated away from one of the ancient landslides, delaying the project by another year. As of 2017, the completion had been pushed back to spring or summer 2019, and the cost had risen to $810 million. The design of the replacement dam allows for future capacity expansion, and the core is wider than needed initially. The design allows the height to be raised by , to quadruple the initial capacity of . On completion of the replacement dam, a third of the old dam was removed to allow the reservoir to be impounded by the new dam instead. The construction project allocated funds to restore populations of native fish in other parts of the watershed. A ladder for Steelhead trout (Oncorhynchus mykiss) at the dam itself was deemed infeasible. At 290 feet (88 m), it would have been the tallest fish ladder in the US and would have cost $40 million. The SFPUC did assure environmental groups that it will release water from the replacement dam to improve summer flows. A smaller fish ladder is under construction at a separate diversion dam on upper Alameda Creek, regarded as prime trout habitat.


Ecology

Facing legal challenges to release flows to support
steelhead trout Steelhead, or occasionally steelhead trout, is the common name of the anadromous form of the coastal rainbow trout or redband trout (O. m. gairdneri). Steelhead are native to cold-water tributaries of the Pacific basin in Northeast Asia and N ...
(''Oncorhynchus mykiss'') in the of Calaveras Creek below the dam, the
San Francisco Public Utilities Commission The San Francisco Public Utilities Commission (SFPUC) is a public agency of the City and County of San Francisco that provides water, wastewater, and electric power services to the city and an additional 1.9 million customers within three San Franc ...
(SFPUC) began steady releases after the dam was re-built in 2018. The steady flow releases, and accompanying lowered water temperatures, resulted in a sharp increase in the numbers of trout.


Plane crash discovery

In the late 1980s and early 1990s, a drought affected California, and water levels in reservoirs throughout the state became extraordinarily low. By January 1991, the water at the reservoir was down , and the aluminum body of an airplane became visible. Two skeletons were found at the site on January 5, 1991. Dental records and the plane's serial number were used to positively identify the remains as Clifford Gillman and his single-engine
Ercoupe The ERCO Ercoupe is an American low-wing monoplane aircraft that was first flown in 1937. It was originally manufactured by the Engineering and Research Corporation (ERCO) shortly before World War II; several other manufacturers continued its ...
, along with Gillman's friend Robert Louviere. They had been missing since June 16, 1963. The wreck, minus the two men's remains, is still lying in the center of the reservoir.


See also

*
Arroyo Hondo (Santa Clara County, California) Arroyo Hondo is a northwestward-flowing U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map, accessed March 15, 2011 river in Santa Clara County, California, United States, that lies east of Milpita ...
*
Black Mountain (Milpitas, California) Black Mountain, also known as Mount Day, is a mountain in the Diablo Range of eastern Santa Clara County, California, east of Poverty Ridge and Arroyo Hondo, and about from Milpitas. The peak is one of the highest in area. The northern half ...
*
List of dams and reservoirs in California Following is a list of dams and reservoirs in California in a sortable table. There are over 1,400 named dams and 1,300 named reservoirs in the state of California. Dams in service :''Please add to this list from the below sources.'' Former ...
*
List of lakes in California There are more than 3,000 named lakes, reservoirs, and dry lakes in the U.S. state of California. Largest lakes In terms of area covered, the largest lake in California is the Salton Sea, a lake formed in 1905 which is now saline. It occupies ...


References

* Loomis, Patricia. ''Milpitas: A Century of Little Cornfields''


External links


San Francisco Water Sources, including Calaveras Reservoir
{{authority control Reservoirs in Santa Clara County, California Hetch Hetchy Project Reservoirs in California Reservoirs in Northern California 1925 establishments in California