Board of Directors
Chair:
Sally Gaines
Martha Davis
Vireo Gaines
David Kanner
Gina Radieve
Tom Soto
Sherryl Taylor
Doug Virtue
Kristine Zeigler
Directors Emeriti
Ed Grosswiler
Richard Lehman
Executive Director
Geoffrey McQuilkin
Southern California Office 1718 Wellesley Ave Los Angeles, CA 90025-3634
On the Internet monolake.org monobasinresearch.org
P.O. Box 29
Hwy 395 and Third Street
Lee Vining, CA 93541
Phone (760) 647-6595
Fax (760) 647-6377
April 15, 2025
Erik Ekdahl
Deputy Director, Division of Water Rights
State Water Resources Control Board
Sent via email
RE: Mitigation of malfunctioning LADWP rotovalve impacts on Rush Creek
Dear Mr. Ekdahl,
Malfunctioning Los Angeles Department of Water and Power (LADWP) infrastructure at Grant Lake Reservoir is preventing LADWP from complying with State Water Resources Control Board license conditions designed to restore the trout fishery, riparian resources, and geomorphology of Rush Creek, which were extensively damaged by decades of excessive water diversion by LADWP.
The Mono Lake Committee (MLC) proposes interim reservoir management requirements designed to mitigate the Stream Ecosystem Flow impairment caused by the malfunctioning valve by maximizing the potential for reservoir spill. This proposal is discussed below and provided in detail in Appendix A.
In 2024, the State Water Board issued an Order approving Temporary Urgency Changes to the Stream Ecosystem Flows because LADWP infrastructure at Grant Lake Reservoir “currently has a malfunctioning outlet valve, referred to as the rotovalve, that can no longer be safely operated to release flows higher than 175 cfs.”
Due to the damaged rotovalve, LADWP plans to submit a Temporary Urgency Change Petition (TUCP) request again in 2025. In fact, based on the repair timeline in LADWP’s December 30, 2024, report on the Grant Lake Reservoir Outlet, LADWP can be expected to submit TUCPs in 2026, 2027, 2028, 2029, 2030, and quite possibly additional years after that.
Waiving Stream Ecosystem Flow requirements for seven or more years is a substantial departure from the restoration program for Rush Creek, creating unreasonable effects on the program and the fish, wildlife, and instream resources. While the failing infrastructure is of understandable concern, it is in the public interest to take all reasonable steps to reduce the negative impact of this situation on the restoration of Rush Creek and the health of the fishery and habitat.
With due diligence LADWP can anticipate and mitigate its multi-year inability to meet the Stream Ecosystem Flow requirements, in particular its impairment of the peak flow releases.
Simply put, planned spills of Grant Lake Reservoir will mitigate the impairment of the required peak Stream Ecosystem Flows (SEFs) to Rush Creek through the malfunctioning rotovalve.
Delays on a long path toward restoration
LADWP water diversions from the Mono Basin began in 1941. Decades of diversion of the full flow of Rush Creek caused the loss of the trout fishery and collapse of miles of riparian ecosystem between Mono Lake and the point of diversion at Grant Lake Reservoir. Court orders in the 1980s required the return of flow and a restoration program, and the State Water Board instituted these requirements and a scientific study program to optimize restoration in LADWP’s water licenses in the 1990s.
The State Water Board Stream Scientists produced a Synthesis Report in 2010 setting forth a plan to restore the streams, primarily through optimizing the water volumes set by the State Water Board into multi-segment flow patterns designed to reactivate natural processes. These flow patterns, known as the Stream Ecosystem Flows, were agreed to by LADWP, MLC, the California Department of Fish and Wildlife, and California Trout in a 2013 settlement agreement and were ordered by the State Water Board in 2021.
LADWP has not yet been able to fully deliver the SEFs due to the limitations of its Grant Lake infrastructure. The license requires construction of an outlet to overcome this obstacle, and it was scheduled to be operational by now.
The malfunctioning rotovalve has already delayed construction of the Grant outlet. Now it is generating multiple years of TUCP requests that, without mitigation, threaten to move the restoration process backward by impairing the Stream Ecosystem Flows. As Monitoring Director Bill Trush noted in his May 2024 report, the SEF requirements are intended to restore Rush Creek’s capacity for self-renewal, something impaired peak flows cannot do.
Reservoir spill can reduce, and in some cases eliminate, impairment of the Stream Ecosystem Flows
The malfunctioning rotovalve TUCP requirements should do everything possible to mitigate the loss of spring SEF flow segments until the required Grant outlet (License condition 13) is reliably designed, constructed, and fully operational.
The most direct mitigation is to spill the reservoir to supplement what LADWP can release through its damaged rotovalve and reduce or eliminate the loss of the SEFs for Rush Creek.
Current reservoir management rules were designed with the expectation of the rotovalve being fully operational up to a maximum of 380 cubic feet per second (cfs). Interim, adaptive reservoir rules would offset the impaired rotovalve capacity of 175 cfs (and any future safety restrictions) by keeping the reservoir higher in all years to increase the probability of reservoir spill in the peak runoff season. Reservoir spill will supplement the flow of water through the malfunctioning rotovalve to Rush Creek. This spill can potentially achieve the SEF flow requirement, and it certainly will reduce the level of SEF impairment. MLC proposes these interim rules be operational until the Grant Lake Reservoir infrastructure is repaired and the Grant outlet is operational.
Rush Creek flow in 2024 provides an instructive example of this approach. In 2024 the 175 cfs rotovalve limitation was in place and a TUCP was issued granting permission to reduce peak flow by about half (205 cfs) to 175 cfs. Fortunately, Grant Lake Reservoir was near capacity entering 2024 and spilled at a level and duration that resulted in Rush Creek flow meeting the SEF requirement.
In 2024, the high reservoir facilitated a spill that mitigated the impact on Rush Creek resources of the malfunctioning rotovalve. This demonstrated the potential for interim reservoir management rules to produce spill and reduce the multi-year impacts on Rush Creek resulting from the damaged LADWP infrastructure.
MLC has used eSTREAM and information from SCE’s Rush Creek Hydrology Model to propose interim adaptive reservoir rules that produce reservoir spill, such as seen in 2024, and offset malfunctioning rotovalve impairment of Rush Creek. MLC’s analysis shows such Interim Rules provide Rush Creek benefits across the board.
An additional mitigation benefit of this proposal is that spring and summer spill, and the associated high reservoir management level, provide significant thermal benefits for the fish population by preserving and delivering cooler water to Rush Creek. As Monitoring Director Ross Taylor noted in his 2024 report, “The primary stressor to Rush Creek’s trout population still appears to be unfavorable summer water temperatures in drier years and/or when GLR has lower storage going into the summer ... Thus, when feasible, LADWP should strive to keep GLR as full as possible heading into each spring and early-summer.”
MLC’s proposal is designed to minimize the chance of winter spill or Storage Management Release (SMR) exceeding 90 cfs (the threshold of concern noted by Monitoring Directors Bill Trush and Ross Taylor), which can negatively impact fish incubating in spawning gravels. It is important to note, however, that the winter flow level of concern is more than three times the flow specified in the license, thus the amount of spill/SMR is the key consideration and minor spill is acceptable. Further, the impact of winter spill must be compared to the impact of multi-
year SEF impairment since LADWP’s malfunctioning rotovalve requires unfortunate choices between resource impacts.
Using SCE-adjusted Rush Creek hydrology to represent current conditions, MLC found that a reservoir well-below capacity is a much bigger liability for Rush Creek than a reservoir near capacity. In the handful of years where winter spill is a threat (usually going into an Extreme-Wet year), SMRs can be used to avoid a spill while keeping Rush Creek flows below desired thresholds.
MLC’s reservoir management proposal is a low-cost mitigation compared to other possible mitigations, such as temporary facilities to pump water out of the reservoir and over the spillway. LADWP has constructed such projects in the past (e.g. in 2010) to ensure compliance with flow requirements.
In 2024, MLC provided written comments on the TUCP proposal that recommended managing Grant Lake Reservoir to facilitate a spill. MLC also expressed concern about the multiple-year proposed work plan to fix the rotovalve and requested the State Water Board consider cumulative impacts of multi-year impairment of Rush Creek flows. Now in 2025 MLC has conducted additional modeling and appreciates the opportunity to provide a detailed proposal that mitigates long-term damage to Rush Creek.
LADWP’s malfunctioning rotovalve at Grant Lake Reservoir is substantially impairing the release of water required by the State Water Board to restore Rush Creek, generating cumulative impacts across multiple years. Due to the impairment of Stream Ecosystem Flows that can be anticipated until 2030 or later, MLC urges the State Water Board to establish interim reservoir management rules that promote reservoir spill to mitigate the impacts on Rush Creek fish, wildlife, and instream resources until LADWP repairs are complete and required Stream Ecosystem Flows can be delivered through regular facility operations.
MLC would be happy to discuss this proposal further. Please contact Bartshé Miller at bartshe@monolake.org regarding follow-up, questions, and discussion.
Sincerely,
Geoffrey McQuilkin Executive Director
CC
Jessica Bean, State Water Resources Control Board
Erin
Bender, State Water Resources Control Board
Mina Mohammadzadeh, State Water Resources Control Board
Janisse Quiñones, LADWP
Anselmo Collins, LADWP
Adam Perez, LADWP
Eric Tillemans, LADWP
Heidi Calvert, California Department of Fish and Wildlife
Alisa Ellsworth, California Department of Fish and Wildlife
Graham Meese, California Department of Fish and Wildlife
Ryan Cooper, California Department of Fish and Wildlife
Sandra Jacobson, California Trout
Redgie Collins, California Trout
Proposed Interim Adaptive GLR Storage Rules
To mitigate impairment of required Stream Ecosystem Flows
Until LADWP repairs to facilities at Grant Lake Reservoir are complete
Proposed Interim Adaptive Grant Lake Reservoir Storage Rules to mitigate impairment of required Stream Ecosystem Flows until LADWP repairs to facilities at Grant Lake Reservoir are complete
The table below is a replacement for MBOP Table 8-1 “Lower/Upper Storage Targets” until LADWP repair work and outlet construction at Grant Lake Reservoir are completed.
No Storage Management Releases (SMR) or exports below the minimum level.
Maximum level can be maintained through SMRs and exports.
1 In order to spill the reservoir, in years when peak SEFs are required, no exports or SMRs should occur prior to the peak flow during the period April 1–July 31. After the peak flow, exports and SMRs can begin to occur consistent with the August–October targets. In Dry and Dry-Normal I years, no SMRs should occur prior to October in order to keep the reservoir as high as possible going into the next runoff year.
2 The 42–45 TAF range for triggering SMRs should be informed by relevant modeling and current conditions and discussions with the SMT and parties. In a year like 2024–25 (a relatively dry winter), the upper 45,000 acre-foot target should be used in order to keep the reservoir as high as possible. In a year like 2016–17 (a winter leading into an Extreme-Wet year), the lower 42,000 acre-foot target should be used in order to keep the reservoir as low as possible. Modeling 2016–17 with the 42 TAF target shows SMRs beginning January 1 would delay spill until April 1 while maintaining releases below 90 cfs.
We used eSTREAM version 9-3 to run a 1983 start with April 1, 2024 starting conditions. This version was used instead of version 9-4 because it included more recent years that reflect current SCE operations. Only years with Gem Lake Reservoir storage management similar to post-2012 operations were closely analyzed—the other years were still used for guidance when appropriate, knowing that in those years more flow would be stored upstream April–July and released August–March. For example, if an April 1 GLR storage minimizes the decrease in peak SEF during a non-representative year when Gem stored more water, it is likely that under current operations when Gem stores less water the April 1 storage would also perform well. Those years must be used with care and are less usable for evaluating the period prior to April 1st
The following focus years were used, especially for fall-winter storage rules, because they represent current SCE reservoir operations:
We started with GLR storage rules based on our analysis of 2024, which indicated that a 40,000 acre-foot minimum storage would be protective of the Rush Creek SEF peak in a Normal year type like 2024. We graphed the storage, storage rules, and SMR for each of the years in the table above and iterated on these rules until arriving at rules that would be protective in all year types with peak SEFs, generally:
• 46,000 acre-feet February–March, lower in Dry
• Spilling April–July (in years when a peak SEF is required)
• Lowering the reservoir in August in order to allow export, SMR, and make room in the reservoir for Lee Vining Conduit diversions during September–October fish monitoring and to avoid spills October–March
• 40,000 acre-feet August–January in order to manage eSTREAM using the Lower target storage for both the upper and lower target
We ran iterations of the February–March storage at 44,000, 42,000, 40,000, 38,000, 36,000, 34,000, and all year draft MBOP rules. This sensitivity analysis allowed detection of where
SEF spill volume decreased, which was used as an indicator of risk and where to set the lower storage threshold. This relationship between April 1 storage and SEF spill peaks determined the minimum April 1 storage target for each year type. To be safe, the worst-performing year was used for all February–March rules (44,000 acre-feet). The Dry year target moves down to 40 TAF in April once the year type is known, and the Dry-Normal I target is kept at 44 TAF in April in case it moves up to DNII in the May forecast.
Our proposed upper storage thresholds, above which SMR would occur, were determined based on expert judgement since the eSTREAM model does not implement its Upper storage targets. The rationale for these is to maintain the reservoir as high as possible in the driest years (in case the next year requires a peak flow), release SMRs prior to October and avoid them in November–December, avoid SMRs over 70–90 cfs January–March, and avoid spills October–March.
We subsequently used SCE current conditions hydrology to evaluate more years outside the eSTREAM model, and that analysis confirmed that these GLR storage targets are appropriate. The worst-performing year of each year-type confirmed that an April 1 storage of 44,000 acrefeet is a prudent minimum storage in all years.
Notes
• If the MBOP revision submitted by LADWP to the State Water Board in 2024 has not yet received final approval, then this table should take precedence over Amended Licenses conditions 11.b.(2) Storage Rules and Criteria, 12.c. regarding D, DN, and N targets, and 12.d. regarding E and EW targets. These targets in the Amended Licenses as well as those in the Draft MBOP are outdated and fail to account for current SCE conditions, the current Grant outlet configuration, capacity, state of disrepair and risk of failure, and current knowledge of the reservoir’s temperature effects on the Rush Creek fishery. The 2024 AOP’s proposed SMR threshold of 46,000 acre-feet is also insufficiently protective of Rush Creek in all but the driest year types, and should be modified to match this table if the reservoir is managed higher.
• In DNI years, the Proposed Interim Adaptive rules keep GLR at 44,000 acre-feet of storage in April in case the May forecast results in a DNII year-type (that would require a peak SEF). If the year type remains DNI, the subsequent reduction in storage in May to 40,000 acre-feet can produce an SMR if not exported. There are two additional benefits that would be increased in DNI years if a peak flow of 175 cfs is released in that year type as mitigation and a SMR: Abundant productive benthic macroinvertebrate riffle habitat (at 40–110 cfs) and off-channel spring/early-summer streamflow connectivity (at 90–160 cfs). An increase in the number of good days and years for these benefits could be achieved in all DNI years if the SMR is released as a 175 cfs peak flow. The State Water Board should consider the possibility of this additional mitigation in DNI years.