Mono Basin Clearinghouse
Real-time Data Companion Page:
Explanations and links to additional resources in this frame (load only this frame/pop up this frame) courtesy of the Mono Lake Committee.

SWRCB Orders Requiring Flows and Lake Levels:
D1631 / 98-05 / 98-07 / 2021-0086 EXEC: License 10191 & 10192 (links coming soon)
Mono Basin Operations Plan (MBOP - in development)
Grant Lake Operations and Management Plan (GLOMP)
Stream Restoration Plan
Waterfowl Habitat Restoration Plan

Eastern Sierra and Nearby Snow Sensors:
Agnew Pass / Dana Mdws / Ellery / Gem Pass / Tioga Pass / Tuolumne Mdws / Virginia Lake Ridge

The 2022 Runoff Year (April 1 2021- March 31 2022) April 1st Forecast is 70,900 acre-feet, or 60% of the 1971-2020 average. It is a "Dry" Runoff Year. Average runoff used in D1631 for Rush, Lee Vining, Parker, and Walker Creeks is 122,124 af based on the 1941-1990 period, although the currently used average (1970-2020) is 118,170 af. The 50-year average is advanced every 5 years. The information in this frame was last updated on May 31, 2022 (it is typically updated once or twice a year). Click here for the latest hydrology updates.

Runoff year definition:
Dry 80-100% exceedance (68.5% of average runoff)
Dry-Normal 60-80% exceedence (68.5% - 82.5%)
Normal 40-60% exceedence (82.5% - 107%)
Wet-Normal 20-40% exceedence (107% - 136.5%)
Wet 0-20% exceedence (over 136.5%)
Extreme-Wet (over 160%)

(counter-clockwise on map)

In early 2021 LADWP was submitting Temporary Urgency Change Petitions (TUCPs) every six months in order to release the new and improved Stream Ecosystem Flows (SEFs) specified in the 2010 Synthesis Report and 2013 Settlement Agreement. On October 1, 2021, the State Water Board issued Order 2021-0086 EXEC, which implements the Settlement Agreement via the two amended licenses 10191 (water) and 10192 (power). These two licenses, which have not yet been posted on the State Water Board's Website, have almost identical terms and conditions, which are summarized below.

The date when it was read is not shown (it is usually read once or twice a month). The 5/31/22 value (6379.4 LADWP datum; 6379.72 USGS datum read on May 16th) is correct (you add 0.37 feet to convert the LADWP datum to USGS--the Water Board and almost all reports and studies use the USGS datum, so this conversion must be made to make this reading meaningful). More information (and sometimes more recent levels) can be found on the Mono Lake Website. The State Water Resources Control Board intended that Mono Lake reach 6,391 by 2014, even though that would have required wetter-than-average climate. The Settlement & Order 2021-0086 EXEC deferred the date that triggered a hearing to 2020. Since the lake didn't reach that level by 2020, "the State Water Board will hold a hearing to consider the condition of the lake and the surrounding area, and will determine if any further revisions to this amended license are appropriate." As of May 2022, the hearing has not yet been scheduled.

Second largest creek in the Mono Basin. More background here. "Above" the diversion is controlled most of the time by what SCE releases from upstream reservoirs. Stream Ecosystem Flow (SEF) this year: Oct 1-Mar 31 minimum flow of 16 cfs, Apr 1-Sep 30 minimum flow of 30 cfs with a bypass flow of 30-173 cfs when the creek "above" is between 31 cfs and 250 cfs, and no diversions when the creek is over 250 cfs. Note: The flows "below" are incorrect when the Langemann gate is in certain positions. On 5/31/22 the displayed flows appear to be correct, but use caution in interpreting flows when flows are rapidly changing.

This is the route by which water is diverted to Grant Lake Reservoir from Lee Vining Creek (and formerly Walker Creek and Parker Creek, which are no longer diverted). Diversions are allowed in order to maintain the creek "below" at or above the required SEF. Augmentation of Rush Creek SEFs with Lee Vining Creek water (via the Aqueduct Conduit) is prohibited, except when required for cooling Rush Creek in Dry or Dry-Normal I years when Grant Lake Reservoir is below 25,000 AF of storage July 1-Oct 1 (this rare situation occurred in 2021 and will occur again in 2022). Note: "Aqueduct Conduit" plus "Lee Vining Creek below" should equal "Lee Vining Creek above," within about 1 cfs, although this check may not work when flows are changing rapidly.

Smallest of the four formerly diverted streams. More background here. The entire flow is to be released in all years. A sediment bypass procedure is being tested that drains the diversion ponds at the diversion dams during the peak flow in non-Dry years. On 5/31/22 the displayed flow was incorrect (Above should equal Below).

Second smallest of the four diverted streams. More background here. The entire flow is to be released in all years. A sediment bypass procedure is being tested that drains the ponds at the diversion dams during the peak flow of non-Dry years. On 5/31/22 the displayed flow was incorrect (Below was 2 cfs higher than Above).

The only time this will show a flow is when Grant Lake Reservoir is spilling (currently at or above 7130.0 elevation, but this will change in the near future). Grant spilled for 32 days June 16-July 17, 2019, with total outflow peaking at 497 cfs on two days. The reservoir spilled in 2017 from June 1st until July 29th. In 2011 the reservoir spilled from March 29th until August 16th. The minimum (combined spill plus release) peak for 2019 prescribed by the Synthesis Report for a Wet year was 650 cfs for 5 days, however it failed to reach this flow during the spill due to operations at upstream dams and the lack of an adequate Grant Dam outlet. In 2011 the goal was also 650 cfs for 5 days (total Rush Creek flow below the reservoir), and an attempt made by LADWP and SCE to test this failed, only reaching 468 cfs despite the occurrence of a (calculated) unimpaired natural peak flow of nearly 800 cfs. In 2017 the minimum peak SEF magnitude for an Extreme-wet year of 750 cfs was almost achieved, with a peak total outflow of 742 cfs. Construction of new outlet gates in the spillway capable of reliably releasing the required peak SEFs is happening during the next couple of years. On 5/31/22 the zero flow was correct, and it is expected to be zero all year.

Largest creek in the Mono Basin. This is the flow "at damsite," or what is coming into Grant Reservoir. It is usually controlled by SCE's releases from upstream reservoirs. Prior to 2012, SCE was required to maintain its reservoirs near spill from July 1 to September 1, causing low flows during the spring and early summer, near-natural flows while they were full, and relatively high flows in the fall and winter when the reservoirs were slowly drained. Starting in 2012, seismic safety drawdown orders required Waugh Reservoir to be kept below 1,555 AF of storage (formerly capacity was 5,277 AF) and Gem Lake Reservoir to be kept 10 feet below the spillway (below 10,752 AF, or 62% of 17,228 AF capacity) and Agnew Lake Reservoir to be kept empty. Seismic retrofit work initially had been expected to be finished in time for the 2017 recreation season however SCE modified the dams to comply with a permanent drawdown. Agnew Dam was modified to be flow-through in 2017, the Waugh Dam spillway was lowered in 2018, and in 2021 the Gem outlet valve was replaced. As part of the current FERC relicensing the dams will be further modified (or partially removed in the case of Waugh). This last decade of non-fill operations results in higher spring-summer flows and lower fall-winter flows than pre-2012 operations. In 2014 SCE began a hydropeaking operation (on Rush Creek and Lee Vining Creek) causing at-times dramatic daily and week-to-week fluctuations (click on the number to see the last 5 days). More background here. On 5/31/22 the displayed flow was correct.

The "full" level of the reservoir is 7130.0 feet, equivalent to 47,171 acre-feet of storage (contrary to older sources, which say 47,575 af). In non-dry years DWP is required to seek to keep Grant between 30,000 (7113.2') and 35,000 acre-feet (7118.4') on April 1, and above 40,000 acre-feet (7123.4') in wet years. DWP must keep Grant above 20,000 AF between July 1 and September 30. Below 26,200 acre-feet (7108.9') the marina has difficulty operating (no safe harbor), below 25,000 acre-feet warm summer water releases become a significant problem for the fishery below the dam. Below 22,800 acre-feet (7105') the boat ramp is out of the water. Below 23,000 acre-feet (7105') the outflow in the Rush Creek Return Ditch can be noticeably turbid--on March 6, 2021 at 23,000 acre-feet (7105') the outflow was milky following a strong wind event. Below 15,000 acre-feet (7094.5') high levels of turbidity are released from the reservoir that sometimes violate water quality rules, and dust storms rise from the back bay. DWP is never required to reduce storage below 11,500 acre-feet (7089.3') in order to provide instream flows higher than inflow, and exports must stop if necessary to maintain at least this level of storage. The bottom of the 7' 8" outlet pipe is 0 acre-feet (7066.8'). The Water Board-approved GLOMP specifies 12,000 acre-feet as the minimum operating level in 2022. Click here to see Grant Lake Res. storage at the end of the previous month. On 5/31/22 the displayed elevation was correct.

The outflow should be equal to the "Rush Creek Return Ditch" (measured at the lower end of the ditch) plus "West Portal" plus the losses in the Mono Gate One Return Ditch. As of May 2017 this station read far too high, and it was too high during spring 2018 high flows, and from late October through late November 2018 it was reading about 10 cfs too high. It is set for a certain range of outflow and is incorrect outside that range--it is very accurate above 110 cfs. It has not been over 110 cfs in two years. On 5/31/22 the displayed flow was close (about 1 cfs too high).

This ditch is currently the only reliable route through which a controlled release of water can be sent down Rush Creek. It was upgraded in 2003 to carry a maximum capacity of 380 cfs and was tested to this capacity in 2004. In prior years the low capacity limited Stream Restoration Flows (SRF) and Channel Maintenance and Flushing Flows (CMF) below those ordered by the Water Board. In 2009 Mono Gate One at the head of the ditch was rebuilt so that flows exceeding 350 cfs could be safely delivered, however in 2010 the ditch was no longer operated above 350 cfs because the lack of maintenance increased the risk of levee failure, and pumps were temporarily installed to deliver 30 cfs over the spillway. It was tested to capacity in 2011 under close watch and with frequent patrols, and DWP identified solutions to the maintenance problems, which were implemented in August 2016. According to DWP, the capacity is once again 380 cfs when 24-hour patrols are available, and it was operated at 380 cfs for about a week in 2017 and again for five days in June 2018. In 2019 it was operated at 351-355 cfs for 29 days (the spill made a release of 380 cfs in the ditch unnecessary). In a Normal year, a peak SEF of 380 cfs for 3 days is required. New Stream Ecosystem Flows (SEF) require in Normal years a minimum flow of 40 cfs April 1-30, rising to 80 cfs May 15-June 11, rising to 120 cfs June 15-July 15 with a 380 cfs peak for 3 days, dropping to a summer baseflow of 30 cfs by August 17, and a winter baseflow of 27 cfs by October 1st. In Dry years (and the rules for 2022), SEFs are 30 cfs April 1-30, rising to 70 cfs May 18-July 6, descending to a summer baseflow of 30 cfs by July 28, and holding until a winter baseflow of 27 cfs beginning October 1st. On 5/31/22 the displayed flow was correct.

West Portal flow is DWP's measurement (starting in 2018 this is a measurement instead of an approximation) of what is flowing from Grant Lake Res. into the Mono Craters Tunnel. East Portal, the outlet of the tunnel at the Upper Owens River, will usually be about 10-15 cfs higher due to groundwater seepage (about 60% of this "Tunnel Make" comes from the Mono Basin aquifer and no longer flows to Mono Lake). The amount of annual surface water export is limited by Mono Lake level and minimum flows and Grant Lake Reservoir storage. When Mono Lake is at or above 6380 feet above sea level on April 1st, a maximum of 16,000 acre-feet (22 cfs on average) of export is allowed until the next April 1. When Mono Lake is between 6377 and 6380 on April 1st and Mono Lake is expected to remain above 6377 based on the May 1 projection and subsequent projections, a maximum of 4,500 acre-feet of export is permitted between May and the following March. No export is allowed when the lake is predicted to drop below 6377 feet. In RY 2022 Mono Lake started the year below 6380 and up to 4,500 acre-feet of export is permitted. Note: the flow shown for West Portal prior to 2018 was often incorrect. DWP calculated West Portal by subtracting Tunnel Make from East Portal, using Tunnel Make from an old hydrologic report. Normally to check this number, subtract "Rush Creek Return Ditch" from "Grant Lake Res. Outflow", however keep in mind that the return ditch value is measured at the lower end of the mile-long ditch and there are water losses in the ditch, and the Outflow value is incorrect at flows below 110 cfs. Starting in 2018 DWP is measuring West Portal directly at a weir at Mono Gate One, solving the West Portal estimation problem going forward. In 2018 East Portal and Upper Owens River flows were incorrectly shown as elevated for a period of time prior to October 17th, when weed growth was cleared from the flumes.

This data is preliminary and subject to a margin of error. Parker and Walker Creek flows are within roughly 5% of actual and are rounded to the nearest cfs. The rules above do not reflect all temporary variances granted by the Water Board. The last 5 days shows the last read until the next update (instead of showing blanks), so if the value remains identical, then only the first instance should be assumed correct.

Some common errors include the following:

In winter, ice will change the water level in the flumes and show erratic or unusually high readings.

Lightning has caused the data transmission system to go down in the past.

Errors occur frequently. Check the daily report (see link below) to see if the flows match (note that some flows on the daily report are daily averages from the previous day--see below).

Click here for the last 3 months of Northern District Daily Reports, which show preliminary correct figures for most of the stations above (updated only on weekdays). Readings are approximately 7 AM, except Grant Reservoir level and storage are at midnight, and the following stations are previous day 24 hour average daily flows: Rush at Damsite,
Lee Vining Above, Outflow 24 Hr AF Total.

Preliminary data (on weekdays as recently as the previous day) are available from MLC for download as CSV files: 2022 Daily report data / 2022 Real time data. Use with caution--these data may not be correct.

Explanation provided by the Mono Lake Committee. Last updated 5/31/22.