Lakewatch

Mono Lake will never (?) be lower again

by Greg Reis

Mono Lake’s fluctuations this year have almost exactly paralleled those of last year. Since early June, the lake has consistently been 2.3 feet higher than last year. It peaked in early August at 6,382.4 feet above sea level, and as of December 10, it stood at 6,381.8. The salinity has also dropped below 85 grams per liter, the maximum allowed under the Outstanding Natural Resource Water designation.

Theoretically, we’ll never again see Mono Lake this low. According to projections and conditions in the Water Board order, once the lake has achieved its target level of 6,391 feet, 6,382 feet is the lowest level to which the lake would drop during extreme drought.

However, we haven’t achieved the target level yet, and chances are fair that a dry year or two in the near future will drop the lake lower than we see it today. (This is why the lake is expected to take about 20 years to reach the target level, even though it’s been rising quickly since 1994.)

16,000 acre-foot diversions

Annual water diversions from the Mono Basin are set by the Water Board order on a graduated scale (see box) based on lake level. This is the first year since the Water Board decision that the Department of Water and Power (DWP) has been allowed to export 16,000 acre-feet of water. DWP began exporting 20-25 cfs from Grant Lake Reservoir in April, and stopped in early June. On August 16 they resumed exporting as much as 30 cfs, and were expected to reach the halfway point of diversions by the end of October. The full 16,000 acre-feet will have left the basin by the end of March 1998.

Despite the exports, Grant Lake Reservoir began spilling since May 7, and continued for the second-longest time period in history. (The longest period was in 1982.) During a few days in August, the reservoir’s spill provided a clue to other things happening with the water in Grant Lake Reservoir. For four days, the inflow and outflow remained constant. Yet the inflow was 10 cfs greater than the outflow. Where was this water going?

DWP's allowed
Mono Basin Diversions

Based on lake level, DWP can divert
the following as the lake rises to the
target level:
Under 6377.....................no diversion
6377-6380......................4,500 acre-feet
6380-6391......................16,000 acre-feet

After the lake reaches the target
level, the following diversions are
allowed based on lake level:
Below 6388....................no diversion
6388-6391.....................10,000 acre-feet
Above 6391...................all water in excess
of required streamflows

Assuming the instruments were accurately recording what was happening, the only place this water could have gone was infiltration to the ground and evaporation to the atmosphere. As it turns out, average evaporation from the reservoir in August is 7 cfs.

What is a
"cfs" anyway?

This column often uses the term "cfs," which stands for "cubic feet per second" and is a common unit for measuring flow in streams. One cfs is a cubic foot of water passing a given point every second. There are about 7.48 gallons in a cubic foot, so one cfs would fill up seven one-gallon milk bottles in just under a second. One cfs flowing for 24 hours adds up to 1.98 acre-feet per day, or enough to flood 1.98 acres one foot deep. Multiply this by 365 days in a year, and one cfs flowing for a year would be enough for over 700 families.

So one cfs is a lot of water for people, but not much for a stream. Rush Creek, for example, carries flood flows well over 500 cfs, and meanders along in the fall at low levels around 50 cfs.

As a sidenote for Mono Lake supporters interested in the up-to-the-minute information on streamflows and Mono Lake’s level, I post the current lake level at the top of our web page—www.monolake.org—every week. We’ve also got a table of past lake levels and other recent data, so you may want to visit on your next web surf!

1997–98 winter

The winter is off to a decent start. November and early December storms have brought over a foot of snow to Lee Vining, and the higher mountain areas have seen several feet more than that.

Throughout the winter snowpack measurements are made by automated sensors (verified with springtime snow course surveys in the field) allowing us to track the wetness of the winter, hour by hour. A number of these sensors are available on the Internet and, if you’d like to easily see the latest for the Mono Basin, we’ve got the local favorites highlighted on our web page as well.

Greg Reis is the Committee’s Information Specialist and master of web page tables.

Return to Winter 1998 Newsletter

Last Updated January 07, 2007