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.
The 2018 Runoff Year (April 1 2017- March 31 2018) April 1st Forecast is 100,700 acre-feet, or 85% of the 1966-2015 average. It is a "Normal" Runoff Year. Average runoff for Rush, Lee Vining, Parker, and Walker Creeks is 122,124 af based on the 1941-1990 period, although the currently used average (1966-2015) is 119,103 af. The information in this frame was last updated on November 21, 2018 (it is typically updated in May and October). Click here for the latest hydrology updates.
Runoff year definition:
(counter-clockwise on map)
The Water Board is expected to revise the required stream flows soon. The information below reflects the former rules, with some mention of the new rules, and will be revised to reflect the new rules when they are ordered.
MONO LAKE ELEVATION
The date when it was read is not shown (it is usually read once or twice a month). The reading (as of 11/21/18) has not been updated with the 11/19/18 observation (but is otherwise correct if you add 0.37 feet to convert the LADWP datum to USGS). More information can be found on the Mono Lake Website. The State Water Resources Control Board intended that Mono Lake reach 6,391 by 2014. If the lake doesn't reach that level by 2020, it will hold a hearing to review the status.
LEE VINING CREEK
Second largest creek in the Mono Basin. More background here. "Above" the diversion is controlled mostly by what SCE releases from upstream reservoirs. In 2018 Saddlebag Lake Reservoir was drained by September 1st in order to repair a sinkhole, resulting in much higher flows than usual during summer. This year, April 1 through September 30 minimum flow "below" is 54 cfs (or "above" flow, whichever is less), and October 1 through March 31 minimum flow is 40 cfs (or "above" flow if it is less). The peak flow must be bypassed undiverted, however in order to keep Grant Lake Reservoir higher than 11,500 af, the Stream Restoration Flow (SRF) can be curtailed, as it was this year. In absence of the SRF, the D1631-required 3-day 160 cfs Channel Maintenance Flow (CMF) was only released for approximately 49 hours this year. New Stream Ecosystem Flow (SEF) prescriptions found in the Synthesis Report are on hold pending Water Board approval of a settlement agreement, but would require a wintertime minimum flow of 18 cfs, a summertime minimum flow of 30 cfs with a bypass flow of 30-173 cfs between 31 cfs and 250 cfs, and no diversions would be allowed when the creek is above 250 cfs. Note: The flows "below" are incorrect when the Langemann gate is in certain positions.
This is the route by which water is diverted to Grant Lake Reservoir from Lee Vining Creek, Walker Creek, and Parker Creek. Diversions are not allowed when the creeks are at or below their minimum flows. Normally, augmentation of Rush Creek SRFs with Lee Vining Creek water is only allowed when runoff is greater than 107% of average (up to 50 cfs in Wet-Normal years, 100 cfs in Wet, and 150 cfs in Extreme Wet years) and 7 days after Lee Vining Creek peaks. In Extreme Wet and Wet years augmentation is allowed for a maximum of 15 days, in Wet/Normal years a maximum of 5 days. New Stream Ecosystem Flow (SEF) prescriptions found in the Synthesis Report that would prohibit augmentation are on hold pending Water Board approval of a settlement. 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. On 11/21/18 the displayed flows (above minus below equals conduit) were incorrect.
Smallest of the four diverted streams. More background here. In all years, April 1 through September 30 minimum flow "below" is 6.0 cfs (or "above" flow), and October 1 through March 31 minimum flow is 4.5 cfs (or "above" flow if it is less). Flow through conditions are required during Rush Creek SRFs and anticipated Walker Creek SRFs. DWP did not plan to divert Walker Creek until the diversion facility is upgraded, therefore no diversions occurred in 2007. The approved plan to divert only in "Dry" years when Mono Lake is above 6380 was followed in 2012 and 2013 and 2014, and minimum flows were violated due to the antiquated infrastructure. The Synthesis Report calls for the entire flow to be released in all years, and implementation of this recommendation is currently pending before the Water Board. Currently a sediment bypass procedure is being tested that drains the ponds at the diversion dams during the peak flow. On 11/21/18 the displayed flows were showing since 11/19/18 a "below" flow that was far too high.
Second smallest of the four diverted streams. More background here. In all years, April 1 through September 30 minimum flow "below" is 9.0 cfs (or "above" flow), and October 1 through March 31 minimum flow is 6.0 cfs (or "above" flow if it is less). Flow through conditions are required during Rush Creek SRFs and anticipated Parker Creek SRFs. DWP did not plan to divert Parker Creek until the diversion facility is upgraded, therefore no diversions occurred in 2007. The approved plan to divert only in "Dry" years when Mono Lake is above 6380 was followed in 2012 and 2013 and 2014, and minimum flows were violated due to the antiquated infrastructure. The Synthesis Report calls for the entire flow to be released in all years, and implementation of this recommendation is currently pending before the Water Board. Currently a sediment bypass procedure is being tested that drains the ponds at the diversion dams during the peak flow. On 11/21/18 the displayed flows were showing (since 11/19/18) a "below" flow that was far too high.
Grant came close to spilling in 2018 due to runoff exceeding DWP's forecast combined with low peak flow releases due to the too-low forecast. The only time this will show a flow is when Grant Lake Reservoir is spilling (at or above 7130.0 elevation). The reservoir spilled in 2017 from June 1st until July 29th. It had not spilled since 2011. In 2011 the reservoir spilled from March 29th until August 16th. The minimum (combined spill plus release) peak for 2017 prescribed by the Synthesis Report was 750 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 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. The settlement agreement pending before the Water Board calls for construction of a new outlet capable of reliably releasing the peak flows.
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 are full, and relatively high flows in the fall and winter when the reservoirs are drained. Starting in 2012, seismic safety drawdown orders required Waugh Reservoir to be kept less than half full and Gem Lake Reservoir to be kept 10 feet below the spillway (62% of 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 in 2018 SCE modified the dams to comply with a permanent drawdown. Work to lower the Waugh Dam spillway occurred in 2018. This results in higher spring flows and lower fall flows than pre-2012 operations. In 2014 SCE began a peaking operation (on all three of its Mono Basin power plants) causing at-times dramatic daily and week-to-week fluctuations (click on the number to see the last 5 days).More background here.
GRANT LAKE RES. ELEVATION
The "full" level of the reservoir is 7130.0 feet, equivalent to 47,171 acre-feet of storage (contrary to some 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 is likely to miss this target on April 1, 2019, due to releasing too much water in August and September 2018 as well as delays in implementing the 2013 settlement agreement, which would release lower winter flows specified in the Synthesis Report. 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--in summer 2018 the reservoir stayed higher than this. Below 22,800 acre-feet (7105') the boat ramp is out of the water. Below 20,000 acre-feet (7101') the outflow in the Rush Creek Return Ditch can be noticeably turbid. 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. 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 below which exports are curtailed (in 2009 & 2015 those guidelines were not followed and exports continued), although when below this level, the inflow from Rush Creek or the dry year minimum is the minimum flow in Rush Creek, whichever is less. Click here to see Grant Lake Res. storage at the end of the previous month.
GRANT LAKE RES. OUTFLOW - DO NOT USE BELOW 110 CFS
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 had malfunctioned for many months and read far too high, and it has been too high during spring 2018 high flows. It is set for a certain range of outflow and is incorrect outside that range. In June 2018 it appeared to be correct--it is very accurate above 110 cfs--however from late October through late November it was reading about 10 cfs too high.
RUSH CREEK RETURN DITCH
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 Normal years, April 1 through September 30 minimum flow is 47 cfs, and October 1 through March 31 minimum flow is 44 cfs. If the inflow is less than the minimum, minimum flow is inflow, except minimum is 31 cfs (36 cfs Oct-Mar) when inflow is less than 31 cfs (36 cfs Oct-Mar). In a Normal year, an SRF of 380 cfs for 5 days followed by 350 cfs for 7 days is required, however in 2018 the 7 day bench following the peak was removed due to concerns about Grant Lake Reservoir dropping below 11,500 af of storage. Since a significant proportion of the year's snow fell in April and May after the last snow surveys and higher in elevation than ground measurements, there was greater uncertainty in the runoff forecast than in a year with a more typical precipitation pattern. New Stream Ecosystem Flow (SEF) prescriptions found in the Synthesis Report are pending Water Board approval of the 2013 settlement, and will 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. Lower winter baseflows are expected to reduce high water velocities that are believed to negatively affect the trout fishery. On 11/21/18 the flow appears to be correct.
West Portal flow is DWP's measurement (as of 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 12-15 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 (not by SRFs) 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. A maximum of 4,500 acre-feet of export is permitted between May and the following March 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. No export is allowed when the lake is predicted to drop below 6377. In RY 2018 Mono Lake is expected to remain above 6380 and up to 16,000 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. 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:
Explanation provided by the Mono Lake Committee. Last updated 11/21/18.