Mono Lake and its tributaries streams, Rush, Lee Vining, Walker, and Parker Creeks, flowing from the snow packs of the east side of the Sierra Nevada range, have been severely impacted by human developments over the past 150 years. The export of the water out of the basin starting in 1941 was especially detrimental. Subsequent court actions have found the State Water Resources Control Board (SWRCB), when granting licenses to export, had failed to protect the public trust resources, the licenses shall be revised, and the habitats of the streams shall be restored.
Utilization of the streams flows for the irrigation, hydroelectric power production, and export out of the basin have had the most substantial impacts on the stream habitats. Irrigation diversions dried up the streams downstream of the diversions except during peak runoff flows and caused the groundwater level in the valleys to decline which stressed the existing vegetation and retarded natural regeneration. The irrigation, was primarily to enhance the range for livestock, mainly sheep, grazing also prevented regeneration of large woody vegetation. Most of the areas originally supporting large woody vegetation were revegetated by sage brush and rabbit brush.
Hydroelectric power generation on Rush and Lee Vining creeks by Southern California Edison has attenuated and delayed the peak flows. The attenuation and delay is greater on Rush Creek which has more developed storage capacity at higher elevations. Flows during the remainder of the year tend to higher than normal. There have been occasional instances when system problems have resulted in the stream flows being completely cut off for short periods of time.
Export of power from the Mono basin by the Los Angles Department of Water and Power (LADWP) began in 1941. An enlarged reservoir was constructed on Rush Creek and diversion structures were constructed at Lee Vining, Walker, and Parker Creeks. The out-of-basin exports further attenuated flows downstream of the structures in each of the creeks that had already been affected by irrigation diversions. The diversions facilities on Lee Vining, Walker, and Parker Creeks included settling basins to prevented bedload from entering the Lee Vining Conduit and effectively prevented bedload materials, especially gravel and cobble, from progressing naturally down stream. No provisions were made at the diversions facilities to allow for the upstream passage of fish. The export of water from the basin reduced the flows into Mono Lake causing the lake level to drop from approximately 6,417 in 1941 to 6,372 feet in 1982. The lower lake level caused incision of the streams in their lower reaches which further lower the level of the ground water and stressed the riparian vegetation. The primary interest, in terms of stream habitat restoration related to the export of water from the Mono basin by LADWP, is in the portions of the four streams Rush, Lee Vining, Walker, and Parker creeks, below Grant Lake Reservoir and the Lee Vining Conduit.
Other substantial impacts on the stream habitats resulted from human activities. Flood flows on Rush Creek in 1969 eroded a large accumulation of cobble that had been piled adjacent to the Rush Creek at a gravel quarry operation, distributed this material across the flood plain, and filled the old main channel in many locations, and generally simplified the stream habitat for approximately two to three miles below the quarry site. CalTrans filled a portion of the, then, dry Parker Creek watercourse and this material had to be removed when water was restored to the stream.
A milestone event was the Supreme Court ruling in 1983 that the SWRCB had failed to uphold its public trust responsibilities when it granted DWP the licenses to export water from the Basin. Subsequent court actions directed the SWRCB to reconsider the DWP licenses and to amend them appropriately so the public trust interests would be suitably protected. The court declared the stream restoration objective to be "to help reestablish the conditions which benefitted the fisheries which existed prior to diversion". Minimal flows were established to assure flows below the Lee Vining Conduit diversions and Grant Lake Reservoir throughout the year. The stream courses of Walker and Parker creeks were to be defined and reconstructed as necessary. And, DWP was directed to develop and implement, in consultation with the Mono Lake Committee, California Trout, the Audubon Society, the Department of Fish and Game, the Forest Service, and the SWRCB, a plan for the restoration of the streams. This consultation with the concerned parties led to a recommendation to the Court that a Restoration Technical Committee (RTC) be created with membership including DWP and those parties.
One of the first major restoration actions recommended by the RTC was the restriction of grazing from the riparian zones of the streams. The establishment of minimal flows by the court and the restriction of grazing from the riparian zone by action of the RTC have been, to date, the two most important restoration activities.
A number of research and restoration activities were conducted under the auspices of the RTC with the advice of a separate Planning Team. Research was primarily to determine the status of the stream resources at the present time and to establish, to the extent possible, the condition of the stream resources prior to the commencement of out-of-basin diversions in 1941. Restoration work accomplished in Rush and Lee Vining creeks included the placement of boulders and large woody materials , digging of pools, placement of spawning gravels, revegetation of riparian areas with willow, black cottonwood, and Jeffery pine, especially along Lee Vining Creek, and re-watering secondary channels, primarily along Lee Vining Creek.
In September of 1994, the SWRCB issued Decision 1631 which amended the DWP licenses. Major aspects of the decision were that: (1) Mono Lake shall be restored to a level of 6,392 feet above sea level; (2) Minimum flows and maintenance (flushing) flows shall be provided for each of the streams; and (3) A comprehensive plan shall be prepared "to restore, preserve, and protect the streams and fisheries". Until the habitat restoration plan is prepared and submitted to, and approved by, the SWRCB, Decision 1631 is not a final action.
Dr. Bill Trush, Mr. Chris Hunter, and I were retained by DWP to prepare the stream restoration plan. The first task in the process of preparing a restoration plan was to evaluate the past stream restoration efforts. The general conclusion was that many of the past efforts had not been well designed and had given only short-term benefits. The evaluation made it clear that designed and constructed stream improvements would almost assuredly require periodic maintenance and replacement.
The high, relatively uncontrolled flows on the streams from the near record 1995 snow pack were observed. We judged that the stream habitats had benefitted from the high flows though some individuals felt the stream habitat had been damaged. The entire bedload appeared to have been entrained and redeposited, pools were scoured, point bars and meanders were extended, stream side vegetation was undercut, fines were deposited in riparian areas, side channels were flooded, and the ground water was extensively recharged.
Based primarily on the evaluation of the past restoration efforts and the observations during the 1995 high runoff flows, the judgement was made to relay primarily on natural processes to restore the stream habitats instead of an emphasis on hands-on restoration activities. The energy provided by flows that reasonably simulated that natural hydrograph were judged to be more effectively and efficiently bring about the restoration and long term maintenance of the stream habitats. There was a basic problem on Rush Creek because the existing Grant Lake reservoir facilities which could not guarantee the maintenance flows we felt were necessary.
The recommended maintenance flows were intended to accomplish specific habitat restoration and maintenance objectives with declining expectations as less water is available (extreme, wet, wet-normal, normal, dry-normal, and dry run-off years): mobilize and redistribute the bedload, extend meanders and point bars, scour pools, erode banks (as a source of new gravels), undercut bank vegetation, deposit fines on the flood plain, and recharge the groundwater. We were confident the recommended flow volumes would accomplish the restoration work identified. We were less confident about the duration of flows needed to accomplish the desired work.
A basic rule for stream restoration programs is to have clearly defined and measurable goals so progress toward attainment of those goals can be measured. A fundamental problem with using flow regimes as the mechanism for restoration and maintenance of stream habitats is the difficulty of defining goals. Since a basic objective is to restore the habitat complexity, initial mapping and subsequent remapping were recommended to determine changes in habitat complexity.
Other recommended actions intended to held to help start recovery included placement of large woody debris because a natural source of this material has been lacking for about 25 years and would take at least 40 or 50 years to develop naturally, re-watering several secondary and former primary channels on Rush creek (sufficient re-watering of channels had already been accomplished on Lee Vining Creek), some further planting of willows, black cottonwood, and Jeffery pine in the areas where channels were re-watered to accelerate the restoration of the valley forest and to develop a natural supply of large woody debris, and construction of bypass structures around the diversions on Lee Vining, Walker, and Parker creeks to allow the movement of bedload downstream and fish migration upstream.
The DWP rejected our proposed stream restoration plan, mainly on the basis of our recommended maintenance flows, and prepared their own draft. After receiving comments on their draft, DWP submitted a final plan to the SWRCB which provided higher maintenance flows that had DWP's draft plan but not the magnitude of flows, especially on Rush Creek, we had originally recommended. The final plan also did not provide for the construction of facilities to bypass facilities at the diversions.
Decision 1631 cannot be considered final until SWRCB has reviewed and approved a stream restoration plan.
