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Watershed Institute Institute for Earth Systems Science & Policy California State University, Monterey Bay Robert Curry - Research Director 100
Campus Center, Seaside CA
93955-8001
(831)582-4098; FAX:(831)582-3691
February 28, 2000 Russian River Watershed Council re: Proposal to Conduct Preliminary Feasibility Studies for the Lake Mendocino Bypass Dear Council Members, Steiner Environmental Consulting prepared the Proposal to Conduct Preliminary Feasibility Studies for the Lake Mendocino Bypass, February 1999 and another document called Lake Mendocino Bypass ? Concept Overview. The Concept Overview lists several expected benefits from the proposed bypass around Lake Mendocino including the restoration of access for salmon and steelhead to about 100 miles of river channel. Salmonid restoration is a very worthy goal indeed and should be pursued. However, review of the Proposal to Conduct Preliminary Feasibility Studies document shows that the feasibility study concept is flawed and incomplete. Also, significant conceptual technical shortcomings are revealed through the Steiner proposal text. On page 18 of the proposed feasibility study, the authors state that: The heart of this project is the diversion and screening structure, but the proposed feasibility study excludes it from study. Exclusion of the diversion and screening structure from the feasibility study will make it impossible to determine if the project is feasible. Experience at the Potter Valley Powerhouse has shown that the design of an effective screening facility is extremely difficult and expensive. There is no point in conducting the proposed feasibility study if the diversion and screening structure is not included in the feasibility study. In fact, it makes more sense to study the feasibility of the proposed screening and diversion structure prior undertaking the study of any of the other issues mentioned in the proposal. The conceptual diversion structure shown in Figure 1, 2 and 3 will not be effective in meeting the goals. For example, in order to preserve the flood control function of Lake Mendocino, the bottom of the diversion into the lake would have to be higher than the existing spillway elevation of 764.8 feet. Otherwise, the bypass channel will become the new spillway. The topographic map presented in Figure 1 of this letter shows that the 760 foot contour line crosses the East Fork of the Russian River approximately 4,480 feet (0.84 miles) upstream of the Highway 20 bridge at the northeast end of Lake Mendocino. The diversion would have to be located approximately 350 feet upstream of this point to be above the existing spillway elevation of 764.8 feet. If the dam were raised, the point of diversion would have to be even further upstream to account for the higher spillway elevation. The new point of diversion would retain the flood control value of Lake Mendocino. However, locating the diversion upstream of the Highway 20 bridge will significantly increase the length of the bypass channel and its cost of construction. The new route would require a very significant cut through the mountainside and may require the removal of several homes. In addition, a crossing would have to be constructed under Highway 20. Besides these difficult technical issues, the new point of diversion may require filing for a change in the point of diversion with the Division of Water Rights, further increasing costs and affording a major opportunity for legal challenges through the State. Suppose that the suggestion to construct the screening and diversion structures upstream above the level of the current spillway was rejected in favor of levee across the north end of Lake Mendocino. The construction of a levee across the northern end of Lake Mendocino would be a difficult undertaking and will destroy the major recreational facilities at Lake Mendocino. The marina and main day use areas are located along the north shore. The proposed levee across the northern end of the lake would separate the marina and the main day-use area from the lake. It is important to remember that the recreational area was mandated by the Act of Congress that authorized the construction of Lake Mendocino. Therefore, it is necessary to ensure that the proposed bypass does not infringe on the recreational uses of the lake. The proposed bypass feasibility study does not even acknowledge the impact the project will have on recreation. The only comment the proposal makes is to say, "The lake itself would remain available for recreation and could continue to support its existing warm water fishery." A complete feasibility study must include the impact of the project on recreational uses of the lake. The levee, proposed in Figures 1, 2 and 3 of the feasibility study proposal, would be very difficult to build. The bottom of the diversion would have to be higher than the existing spillway elevation of 764.8 feet. So, the bottom of the diversion would be at least 27 feet above the normal pool elevation of 737.5 feet. The top of the levee would be even higher. The proposed levee will be a very imposing structure. The construction of the levee will require moving the marina and day-use areas from the north shore of the lake. The levee will also result in the loss of the best swimming beach on the lake. Construction of the levee would require removing all the sediments deposited along the length of the proposed path of the bypass, to provide a stable foundation for the levee. The majority of the sediments (80% to 95%) will be fine grained and will not be suitable for placement in the Russian River. All of the sediments will have to be tested for hazardous materials such as heavy metals and pesticides before they are disturbed. If hazardous materials are found, the sediments will have to be trucked to an approved disposal site. This operation could be very expensive. Even if the sediments do not contain hazardous materials, they will be expensive to remove and dispose of. Placing any of the lake sediments in the Russian River will require an easily challenged 404 permit from the Army Corps of Engineers. The feasibility study must include a testing the sediments for hazardous materials. The proposed feasibility study concentrates on determining the size distribution of the sediments and ignores the equally important chemical evaluation. Will a year-round flow be maintained through the bypass? Will the bypass only carrying water during storm events? If the bypass will only operate during storm events, is it possible that steelhead and/or salmon will become stranded in the bypass? These issues need to be discussed in detail for the feasibility study to be complete. One of the critical goals of the proposed bypass channel is to move bedload and bed material load around Lake Mendocino. A principle of fluvial geomorphology is that a natural river channel adjusts its size and channel geometry to accommodate both the discharges of water and sediment, including bedload. This principle indicates that the bypass would have to have roughly the same dimensions and gradient as the channel above the lake to move all of the arriving bedload around the lake. Bedload only moves during high discharge events. A rough estimate for the discharge required to initiate movement of bedload is 80% of the bankfull discharge. A rough estimate of the bankfull discharge is the 1.5-year return period discharge, calculated using the annual maximum discharge series. Figure 2 of this letter shows the return period of the 56 observed annual maximum discharges at the USGS gauging station (11461500) just upstream from Lake Mendocino. The return periods were calculated using the Gumbel Extreme Value method. The 1.5-year discharge is estimated to be 5,750 cfs. So, the minimum discharge to initiate movement of the bed supplied by the East Fork of the Russian River is approximately 80% of 5,750 cfs or 4,600 cfs. The conceptual design of the screening and diversion structure shown in Figures 2 and 3 of the Proposal to Conduct Preliminary Feasibility Studies for the Lake Mendocino Bypass will cause the deposition of bedload at the diversion. The loss of discharge into the lake will also reduce the sediment transport capacity of the bypass. In addition, the constriction required to house the flow control gate may also cause deposition. In other words, you cannot have your cake and eat it too. To pass the sediment while capturing part of the flow is not hydrologically possible. One of the requirements for the bypass channel is no increase flooding below the confluence of the East Fork and main-stem (also known as the West Fork) of the Russian River. This requirement will be met if the maximum discharges from Lake Mendocino remain unchanged or if the flow in the bypass channel equals what would have been released from the lake. Figure 3 of this letter compares the annual maximum discharge released from Lake Mendocino to the annual maximum discharge at the USGS gauging station, just upstream of the lake. If the bypass had been in place when the dam was constructed and if all of the historical flood releases were routed down the bypass, Figure 3 shows that bedload would have moved down the bypass in only 8 out of the 40 years of record. By comparison, the estimated threshold to initiate bedload above the lake was exceeded in 33 out of the 40 years since the dam was completed. Thus, the goals of flood prevention and moving bedload down the proposed bypass conflict. Bedload movement requires flood discharges and flood prevention requires the capture of flood discharges. It is highly unlikely that the proposed bypass could move more than a small fraction of the bedload supplied to Lake Mendocino by the East Fork of the Russian River around the lake. The addition of the storm discharges from the bypass will probably lead to increased scour of the 3.5 miles of the West Fork between Calpella and the confluence with the East Fork. The Russian River above Calpella produces very little bedload. Both the Russian River and Forsythe Creek are actively incising and much of the bed of both streams consists of exposed clay. There are numerous farm ponds in the watershed upstream of Calpella that capture the bedload provided by the surrounding hills. The Ford gravel extraction operation at the north end of Redwood Valley tends to capture the majority of bedload delivered by the Russian River from above the start of Tomki Road. Bedload was measured at the USGS gauging station above Lake Mendocino Drive during the 1990's. The best-fit equation for the observed bedload transport was proportional to the water discharge raised to the 2.2 power. Thus, doubling the water discharge would probably increase the bedload transport capacity by 4.6 times. Consequently, the bedload supplied by the bypass would not be sufficient to offset the deficiency of bedload supplied from the Russian River above Calpella. Thus, the increased in discharge below the confluence with the bypass will probably increase the rate of incision downstream of the bypass even if the some bedload is supplied by the bypass. Over time, the increase in incision below the confluence of the bypass with the Russian River will work upstream and worsen the incision in Redwood Valley and along Forsythe Creek. These considerations show that the Russian River between where the proposed bypass joins the river and the confluence with the East Fork would have to be protected against the increased discharge from the proposed bypass. This would be very expensive. In conclusion, it is unlikely that the proposed bypass will accomplish most of the benefits for hydrology, geomorphology and lake-operations claimed for it in the Lake Mendocino Bypass Concept Overview document. 1.
The discussion in this letter shows that only a small
fraction of the bedload supplied to Lake Mendocino could be
transported around the lake by the proposed bypass. It is
likely that the majority of the bedload will be deposited in
the diversion and screening structure. Removal of this
material from the structure will be an ongoing expense. The main objective of the proposed bypass, providing a means for salmon and steelhead to move past Coyote Dam and Lake Mendocino, is a worthy one. However, the proposed bypass will not effectively move bedload around the reservoir. A superior project would be to concentrate on finding a way to move the fish around the reservoir or to remove the reservoir and restore passage. The goal of restoring salmonids to the East Fork of the Russian River is worthy enough on its own and does not require linking it to other objectives that are unlikely to be obtained. Sincerely, cc: Senator
Barbara Boxer Senator
Dianne Feinstein Col.
Grass Honorable
Lynn Woolsey Honorable
Mike Thompson California
State Senator Wes Chesbro Assemblywoman
Virginia Strom-Martin Assemblywoman
Pat Wiggins Karen
Rippey Maria
Rey Mary
Nichols Tim
Smith Stan
Dixon Supervisor Mike
Riley, Chair Michael
Delbar Jay
Halcomb Linda
Curry Tim
Buckner Miles
Croom Brian
Hunter Lee
Michlin Dennis
Slota Randy
Poole Bob
Muelrath Mendocino
Resource Conservation District Russian
River Flood Control & Cons Dist |