Flows into the Lower Owens River Project (LORP) will commence in 2003. Technical Memorandum #1 describes the manner in which minimum (base) flows of 40 cfs and maximum (riparian) flows of 200 cfs will be delivered to the lower Owens River. While the details of hydrologic control and flow augmentation are given in the first tech memo, details of how the flows will be managed in years 2003 and 2004 have not been described. Both Inyo County and LADWP requested a technical memorandum describing flow management during these "initial years".

    It should be noted that this technical memorandum recommends releasing riparian flows and achieving 40 cfs base flows in the Lower Owens River later than the schedules contained in the MOU. The rationales for the recommended schedules are discussed below.

Purpose

    The purpose of this tech memo is to recommend how flows should be managed, ramped and manipulated to meet both LORP goals and prevent adverse impacts on key environmental conditions during the first two or three years of flow reintroduction. This tech memo also recommends water spreading and flows in the island reach of the Lower Owens River (Task II A5 of the work plan).

Definition of InitialYears

    The first two to three years of the LORP are defined as the "initial" years; the goal is not the release of riparian flows that promote seeding of riparian plants, but simply to reach a base flow equilibrium as early as possible. Flows will be initiated in spring during the first frost-free period. This will avoid problems associated with frozen streambanks or icing in the channel that would prevent filling of bank storage aquifers. Initial flows will be allowed to fill shallow, near-channel aquifers, wetlands and bank storage areas over two to three years.

    An out-of-channel riparian flow of 200 cfs will not be released in the initial years unless flow equilibrium is reached in the channel, fish remain healthy, unstressed and in good condition, and water quality has reached acceptable sustainable levels. Technical memorandum #1 (Hydrologic Plan for Implementing Initial Maximum and Minimum Flows) left the impression that riparian flows will be initiated during the first year; however, large freshet flows too early in the rewatering program could exacerbate poor water quality conditions by mobilizing organic material from adjacent lands and organic sediments from the river bed.

Flow Management in Initial Years

    There are a number of resource issues associated with rewatering the lower Owens River other than simply refilling dry aquifers and bank storage areas. An element of risk is associated with introducing flows too rapidly in the early years, thus careful ramping of flows, based on information and data from intensive monitoring of initial flows, is needed in order to minimize risk and to protect critical natural resources.

Water Quantity Issues

    The goal of providing a year-around base flow to the river is to achieve as close to 40 cfs as possible in all reaches of the river. Tech memo #1 describes losing reaches and gaining reaches, and makes it clear that it is impossible to achieve exactly 40 cfs at all points in the lower Owens River. Nevertheless, it is possible to meet base flow goals throughout the river, with a reasonable amount of variability, once bank storage and groundwater aquifers are filled. The goal of water delivery in the initial years is to fill aquifers in losing reaches and adjust discharge as necessary once a predictable base flow condition is attained.

    Second year flow releases of 40 to 50 cfs will allow a closer evaluation of gaining and losing reaches and will provide better projections of the time required to fill aquifers. Like the first year, second year releases will further fill aquifers and enhance stream bank stabilization. There will undoubtedly be a vegetation response to these flow releases, but this is not the primary purpose of initial water releases.

    Third year flow releases will focus on attaining approximately 40 cfs flow throughout the river by adjusting the delivery system as needed. This may entail manipulating discharge from selected spill gates to augment flows in different river reaches.

Water Quality Issues

    We anticipate two principle water quality problems associated with the rewatering of the river during the initial years. First is the potential for fish kills when water is reintroduced into the river. Second is the short-term influence on water quality conditions. It is possible, however, that correct ramping of flows will avert fish kills and that short term water quality will not become a problem. The approach to handling water quality problems, however, will be to anticipate adverse conditions and to adjust the system as needed.

    During 1993 controlled flow studies the sudden release of large volumes of water caused a fish kill. The fish killed included game fish (largemouth and smallmouth bass, bluegill, and catfish) and non-game fish (carp, suckers, etc.). As flow was increased during the study, ammonia and hydrogen sulfide gases along with larger quantities of muck and cattle waste from floodplains were mobilized. These organic rich materials caused dissolved oxygen to drop rapidly and fish experienced both low dissolved oxygen, toxic gases, and high flows simultaneously. To reach the desired river flow levels necessary for the controlled flow study, water was released from several spill gates. Water in the spill gate channels was high in dissolved oxygen and exhibited low velocities; with increasing water levels the sills between spill channels and the river were inundated. Fish escaped the river’s low dissolved oxygen by moving quickly to the spill channels for refuge. Unfortunately this movement of fish went undetected, and spill gates were closed without first ramping down the flows. As a consequence, fish were killed by stranding in the spill channels. Other fish mortalities occurred in the river as a consequence of low dissolved oxygen and possible ammonia toxicity that occurred when bottom water from beaver ponds was moved downstream.

    The second area of concern is with short term water quality conditions. During the initial years it is possible that dissolved oxygen, ammonia, hydrogen sulfide, pH, temperature, and turbidity may not meet the objectives of the Water Quality Control Plan for the Lahontan Region. In time, however, as the channel is cleared, riparian vegetation increases, stream flows reach equilibrium, beaver ponds no longer affect flows, cattle wastes in the channel and on floodplains diminish, and muck deposits are buffered or assimilated, water quality objectives should be met.

Management Options

    Initial flows will be released into the Lower Owens River in the spring of 2003. To prevent fish kills and minimize stress on existing fish populations from rapidly deteriorating water quality conditions, initial flow introduction should be gradual and carefully monitored. During the period when channels, aquifers and bank storage systems are being re-filled, stream water quality and fish populations will be closely monitored. If water quality conditions should begin to deteriorate to toxic levels, action plans for emergency recovery of fish (catch and transportation to nearby lakes and ponds) may be implemented. Details of emergency fish recovery and protection plans will be provided in the technical memorandum on fisheries and riverine-riparian habitat. However, recommendations for how initial flows should be introduced and management options to respond to adverse conditions are described here.

    The 1993 rapid flow releases indicated that a 30 cfs flow was a water quality threshold. At 30 cfs velocities increased in most river reaches to > 1fps. At this velocity HEC-2 modeling showed that incipient bottom scour begins and surficial, unconsolidated muck deposits are mobilized. Water quality testing indicated that hydrogen sulfide, ammonia, and BOD increased dramatically at this point. While the data collected during 1993 could be indicative of water quality conditions during rapid flow reintroduction, it may not be representative or conclusive for deliberate, incremental rewatering that allows for river assimilation and equilibration. Nevertheless, it should be recognized that a risk may exist for aquatic life at flows approaching 30 cfs in the existing wetted reaches (from Mazourka Canyon Road downstream).

    A two phased flow management approach is recommended during the initial year. The first phase is direct flow releases from the intake that continue until steady-state conditions (in terms of water quality and quantity) are attained at 20 cfs. The second phase minimizes the risk to a part of the wetted reach by augmenting flows from Alabama Gates.

    The key to exercising flow management is continuous water quality monitoring during the early months of initial years. The approximate flow travel time from the intake to Keeler Bridge is 12 days. In that period of time deterioratin tionless near the surface, rapid gill movement, and body condition. Monitoring will be performed at the intake, below Goose Lake, at five culverts, Mazourka Canyon Road, Manzanar Reward Road, below Georges spillgate, at Reinhackle Springs, Lone Pine Ponds, Lone Pine Road, and Keeler Bridge. Monitoring data will be reviewed at 5 cfs intervals and will provide an early warning of water quality conditions and trends and fish health in all reaches of the river. Flow management under the two phases is described below.

Phase I

At start-up of flow reintroduction all discharge will be from the intake until the entire river length reaches about a 20 cfs steady state condition. The flow release on day 1 will be 1 cfs, or as close to that as control structures will allow. The flow will be increased by 1 cfs every 24 hours in 5 cfs intervals. At each 5 cfs incremental flow level (about every 5^th day) monitoring data will be evaluated to determine flow effects on fish and water quality. Once it is determined that there are no adverse effects, or the effects are tolerable, the 1 cfs flow increase each 24 hours will continue. There could be a delay in this regime to allow for equilibration if fish life and water quality are not being adequately protected.

There are several management actions that can be taken depending upon the water quality and fisheries situation. If monitoring indicates a downward trend in water quality, flows can be (1) reduced until water quality conditions improve or (2) held steady until equilibrium is attained and water quality begins to improve. If flow augmentation and steady state flow conditions provide insufficient relief, the fisheries recovery program can be implemented to capture and remove fish to off-channel ponds and lakes. As water quality improves, transplanted fish can recolonize into the river channel.

Phase II

When a steady-state flow of about 20 cfs has been achieved in the river the primary point of discharge will switch from the intake to Alabama Gates. Discharge from the intake will be held steady and flows in the wetted reach will be managed from Alabama Gates. The Alabama spillgate is the last point at which flows can be augmented, thus the aquatic life currently in the wetted reach from Billy Lake return to just below Reinhackle Springs is not placed at risk. Using the Alabama spillgate to bring flows up to and past the 30 cfs threshold only places that reach of the river downstream to the lake at risk. It is also prudent to initiate Phase II at 20 cfs rather than 30 cfs to minimize risk even further.

The flow release from Alabama Gates will be 1 cfs, or as close to that as the control structure will allow. The flow will be increased by 1 cfs every 24 hours in 5 cfs intervals. At each 5 cfs incremental flow level (about every 5^th day) monitoring data will be evaluated to determine flow effects on fish and water quality. Once it is determined that there are no adverse effects, or the effects are tolerable, the 1 cfs flow increase each 24 hours will continue.

 

Monitoring will take place at several locations below Alabama Gates to the delta for the same water quality constituents described above. In the event of deteriorating water quality conditions the same actions described in Phase I will be implemented.

 

Once the flow from Alabama Gates to the pumpback station has reached steady-state conditions (in terms of water quality and quantity) at 40 cfs, flow from the spillgate will be reduced at the rate of 1cfs/day and intake flows will be increased at the rate of 1 cfs/day in 5 cfs increments accompanied by monitoring until the reach from the intake to Alabama Gates also reaches approximately 40 cfs.

 

Responses to changing situations will continue and flows will increase as water quality improves following each event. Until flows are initiated into the river we cannot predict how frequently actions must be taken to adjust for water quality and fisheries conditions. However, we anticipate that intensive monitoring and flow adjustments will only be needed in the first season of rewatering. Water quality and fisheries conditions should improve rapidly after the first season. The focus for the second initial year will be on flows needed to fill aquifers and to establish steady state flow conditions.

Island Reach

    The island reach is in the lower Owens River below Reinhackle Springs in the Alabama Hills area. The river channel aggrades in this reach creating a broad flat area. The channel is essentially undefined and water braids throughout the broad flat, resulting in isolated land areas surrounded by shallow water. Irrigation return flows and spring flows have created a substantial wetlands extending west to east from Highway 395 to the opposite side of the river channel. During the 1993 controlled flow study when flows were released from Alabama Gates water spread and ponding increased dramatically to nearly top Highway 395 immediately south of the Alabama Hills spill gate.

    Flooding the highway obviously poses a risk to human safety as well as potential damage to the road bed. HEC-2 modeling during the controlled flow study showed that even at a base flow of 40 cfs substantial flooding could occur in this reach. However, CalTrans was consulted on this issue and they are comfortable that flooding associated with 200 cfs will not threaten the highway. Nevertheless, long term flooding in this reach will create particular management problems for mosquito control and cattle grazing.

Management Recommendation

    Channels in the island area are remnants and portions of oxbows located mostly on the east side of the river. The riparian flows of up to 200 cfs will eventually reconnect with one or more of these historic channels to carry most of the 40 cfs base flow. The LORP will create literally thousands of acres of wetland and marsh habitat. We expect that a valuable willow-cottonwood riparian forest (rather than additional marsh land) can develop in the island reach in time and with proper land management. We recommend allowing the river to define the channels through the island area relying upon adaptive management to respond to grazing, mosquito, or flooding problems that may arise in the course of time.