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 old; among the oldest lakes in North America.
VOLUME OF MONO LAKE
4.3 million acre-feet at 6417' asl (in 1941 before diversions)
3.1 million acre-feet at 6392' asl (future stabilization level)
2.4 million acre-feet at 6378' asl (2015 level)
2.1 million acre-feet at 6372' asl (1982, lowest recorded level)
The lake level before the diversions of Mono's tributary streams was 6417 feet above sea level (asl). The current lake level is
6381.3 feet asl (approx. 1,946 meters). It is expected to take over 20 years to reach 6392 feet asl, the Water Board-ordered stabilization level. Once it reaches 6392', it should usually fluctuate about 6 feet in elevation and occasionally rise as high as 6400', and during extreme drought, drop as low as 6382'. 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 6355 feet asl with fluctuations of 21 vertical feet. During periods of extreme drought, the lake might have fallen as low as 6336 feet asl.
PAST LAKE FLUCTUATIONS
|20th Century Low, January 1982
||6372 feet asl
|Beginning of Diversions, 1941
||6417 feet asl
|20th Century High, 1919
||6428 feet asl
|Overflow Level, perhaps 100,000 years ago
||7200 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 6392 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.
STATE 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. 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 6377, no diversions are allowed. Between 6377 and 6380, diversion of 4,500 acre-feet is allowed. Between 6380 and 6391, diversion of 16,000 acre-feet is allowed.
Once the lake reaches 6391, a new set of restrictions applies. No diversions are allowed if the lake drops below 6388. Diversion of 10,000 acre-feet is allowed when the lake is between 6388 and 6391. 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 6391. If the lake hasn't reached 6392 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.