DEPTH OF MONO LAKE
Maximum = 158 feet. Average = 56 feet.
AGE OF MONO LAKE
At least 760,000 years old and probably 1-3 million years; among the oldest lakes in North America.
VOLUME OF MONO LAKE
4.3 million acre-feet at 6,417' asl (in 1941 before diversions)
3.1 million acre-feet at 6,392' asl (future stabilization level)
2.4 million acre-feet at 6,378' asl (2015 level)
2.1 million acre-feet at 6,372' asl (1982, lowest recorded level)
The lake level before the diversions of Mono's tributary streams was 6,417 feet above sea level (asl). The current lake level is
6380.4 feet asl (approx. 1,946 meters). It is expected to take over 20 years to reach 6,392 feet asl, the Water Board-ordered stabilization level. Once it reaches 6,392', it should usually fluctuate about 6 feet in elevation and occasionally rise as high as 6,400', and during extreme drought, drop as low as 6,382'. The yearly evaporation rate is approximately 45 inches per year. Click here for more current and past lake levels.
Without restrictions on stream diversions, the lake would have eventually stabilized at approximately 6,355 feet asl with fluctuations of 21 vertical feet. During periods of extreme drought, the lake might have fallen as low as 6,336 feet asl.
PAST LAKE FLUCTUATIONS
|20th Century Low, January 1982
||6,372 feet asl
|Beginning of Diversions, 1941
||6,417 feet asl
|20th Century High, 1919
||6,428 feet asl
|Overflow Level, perhaps 100,000 years ago
||7,200 feet asl
||55,000 acres (86 sq. mi.)
||1941, prior to diversions
||48,900 acres (76 sq. mi.)
||future stabilization level
||42,300 acres (66 sq. mi.)
||1988, 1995, 2015
||37,700 acres (59 sq. mi.)
||1982, lowest recorded elevation
WATER CHEMISTRY OF MONO LAKE
It contains chlorides, carbonates, and sulfates - a chloride-carbonate-sulfate "triple water" lake. It is alkaline, with a pH of 10, and almost three times as salty as the ocean. At 6,392 feet asl it will be slightly more than twice as salty as the ocean.
The salinity of the lake is approximately 81 g/l. The Outstanding National Resource Water designation requires that the salinity be maintained under 85 g/l (the concentration of Mono Lake in May, 1996 and November, 1975). The average salinity levels ranged from 42 g/l to 99 g/l since 1913. Under a full-diversion scenario, the average salinity would have been approximately 133 g/l. Click here for an analysis of mineral quality.
ECOLOGY OF MONO LAKE
The primary lake life is composed of algae, brine shrimp, and alkali flies, and is one of the most productive ecosystems in the world. Nesting birds consist of California Gulls (50,000, 85% of California's breeding population and second largest colony in the world after the Great Salt Lake in Utah) and Snowy Plovers (400, 11% of the state's breeding population). Migratory birds include Eared Grebes (1.5-2 million, 30% of the North American population), Wilson's Phalaropes (80,000, 10% of the world population), Red-necked Phalaropes (60,000, 2-3% of the world population), and 79 other species of waterbirds.
GEOLOGYThe Mono Basin is a tectonic basin formed by faulting and downwarping of the earth's crust. It is from one to three million years old. The hills on the north, south, and east sides of the basin are all of volcanic origin. The Mono Craters are 24 domes of explosive rhyolite that have erupted over the last 40,000 years (as recently as 700 years ago), forming the youngest volcanic chain in North America. Black Point, Negit Island, and Paoha Island are also of volcanic origin. Paoha Island emerged within the last 350 years.
The rain shadow of the Sierra Nevada has a dramatic effect, with an average of over 45 inches of precipitation falling at the Sierra crest and less than 5 inches at the east shore of Mono Lake.
|Lee Vining Ranger Station
|East side of Mono Lake
The median runoff is 93% of average. The minimum observed runoff was 44% of average seen in 1977, and the maximum was 194% of average seen in 1983. The runoff is a product of snowmelt runoff and baseflow from the watershed. The yearly average for all Mono Basin streams is 187,000 acre-feet. Total average inflow to Mono Lake is 230,000 acre-feet, which includes runoff plus groundwater inflow and direct precipitation onto the lake.
WATER BOARD-ORDERED FLOWS
In 1994, the State Water Resources Control Board issued D1631 ordering minimum flows and maintenance flows for all of the diverted streams. Stream restoration plans approved in 1998 modified the maintenance flows somewhat. The minimums are based on a wet/normal/dry year classification and are lower from October through March. These minimum flows range from 25 cfs to 54 cfs for Lee Vining Creek, from 4.5 to 6 cfs for Walker Creek, from 6 to 9 cfs for Parker Creek, and from 31 to 68 cfs for Rush Creek. The results of a 2008 flow study are expected to modify these somewhat. Click here for real-time flows.
The yearly average export from the Mono Basin depends on the level of Mono Lake on April 1. Below 6,377, no diversions are allowed. Between 6,377 and 6,380, diversion of 4,500 acre-feet is allowed. Between 6,380 and 6,391, diversion of 16,000 acre-feet is allowed.
Once the lake reaches 6,391, a new set of restrictions applies. No diversions are allowed if the lake drops below 6,388. Diversion of 10,000 acre-feet is allowed when the lake is between 6,388 and 6,391. All water (estimated to be on average 30,800 acre-feet) in excess of required stream flows (89,000 acre-feet) is allowed to be diverted when Mono Lake is above 6,391. If the lake hasn't reached 6,392 in a timely manner, the State Water Resources Control Board may hold a hearing regarding revision of the rules to allow it to rise faster.