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Twitchell Reservoir
Twitchell Reservoir
	Twitchell Reservoir Twitchell Reservoir
Location	San Luis Obispo / Santa Barbara counties, California, United States
Coordinates	34°59′53″N 120°19′59″W / 34.998°N 120.333°W
Type	Reservoir
Primary inflows	Cuyama River / Huasna River
Primary outflows	Terminal (evaporation) / Cuyama River
Basin countries	United States
Water volume	225,000 acre⋅ft (278,000,000 m3)
Surface elevation	692 ft (211 m)
References	"Twitchell Reservoir". Geographic Names Information System. United States Geological Survey, United States Department of the Interior.

Twitchell Reservoir is a reservoir in southern San Luis Obispo County and northern Santa Barbara County in California. The reservoir has a capacity of 197,756 acre⋅ft (243,928,000 m³) and is formed by Twitchell Dam on the Cuyama River about 66 miles (106 km) from its headwaters in the Chumash Wilderness Area. About 7 miles (11 km) below the dam, outflow joins the Sisquoc River near Garey, CA to form the Santa Maria River.

Twitchell Dam was built by the United States Bureau of Reclamation between 1956 (69 years ago) (1956) and 1958 (67 years ago) (1958). The original names were Vacquero Dam and Vacquero Reservoir, but they were changed to honor T. A. Twitchell of Santa Maria, a proponent of the project. The dam and reservoir provide flood control and water conservation.

The Central Coast of California only receives significant amounts of rainfall during the winter, this area averaging 14 inches (360 mm) per year. The water is stored in the reservoir during big winter storms and released as quickly as possible while still allowing it to percolate into the soil and recharge the groundwater.^[1] This means that the reservoir is usually far from full. It is estimated that the project increases recharge by 20,000 acre⋅ft (25,000,000 m³) annually.^{[citation needed]}

Sedimentation is a problem for the reservoir, as the reservoir is being filled 70 percent faster than expected. This reduces its capacity and blocks the water inlet to the control gates. Some sediment has been removed by flushing it out during releases, but much of it is simply deposited immediately downstream, interfering with flows.

There is no public access to the dam or reservoir.^[2]

Climate

Climate data for Twitchell Reservoir
Month	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Year
Record high °F (°C)	94 (34)	90 (32)	95 (35)	108 (42)	104 (40)	112 (44)	111 (44)	109 (43)	115 (46)	107 (42)	98 (37)	86 (30)	115 (46)
Mean maximum °F (°C)	79 (26)	81 (27)	83 (28)	89 (32)	90 (32)	96 (36)	95 (35)	94 (34)	99 (37)	97 (36)	88 (31)	79 (26)	104 (40)
Mean daily maximum °F (°C)	66.5 (19.2)	66.8 (19.3)	68.2 (20.1)	72.1 (22.3)	73.6 (23.1)	78.3 (25.7)	80.5 (26.9)	81.1 (27.3)	82.1 (27.8)	79.2 (26.2)	72.4 (22.4)	65.5 (18.6)	73.9 (23.2)
Daily mean °F (°C)	53.3 (11.8)	54.3 (12.4)	55.6 (13.1)	58.5 (14.7)	59.9 (15.5)	63.9 (17.7)	66.6 (19.2)	67.1 (19.5)	66.9 (19.4)	64.2 (17.9)	58.3 (14.6)	52.5 (11.4)	60.1 (15.6)
Mean daily minimum °F (°C)	40.4 (4.7)	41.8 (5.4)	43.1 (6.2)	44.9 (7.2)	46.4 (8.0)	49.7 (9.8)	52.5 (11.4)	52.8 (11.6)	51.7 (10.9)	49.2 (9.6)	44.1 (6.7)	39.4 (4.1)	46.3 (8.0)
Mean minimum °F (°C)	29 (−2)	31 (−1)	33 (1)	35 (2)	39 (4)	43 (6)	46 (8)	46 (8)	43 (6)	38 (3)	32 (0)	28 (−2)	27 (−3)
Record low °F (°C)	15 (−9)	19 (−7)	21 (−6)	23 (−5)	29 (−2)	35 (2)	36 (2)	39 (4)	32 (0)	26 (−3)	19 (−7)	18 (−8)	15 (−9)
Average precipitation inches (mm)	3.38 (86)	3.04 (77)	3.26 (83)	1.20 (30)	0.34 (8.6)	0.06 (1.5)	0.04 (1.0)	0.04 (1.0)	0.24 (6.1)	0.83 (21)	1.44 (37)	3.02 (77)	16.89 (429.2)
Source: NOAA^[3]