An opportunity to restore watershed connectivity27 September 2011
Many natural resource professionals have dedicated their working careers to improving existing and re-establishing fish populations in the Yakima Basin in the US, while recent plans to provide fish passage at Cle Elum dam have been met with much enthusiasm. As US Bureau of Reclamation fishery biologist Joel Hubble explains, the ecological and social benefits of reconnecting the upper Cle Elum sub basin to the rest of the Yakima Basin cannot be underestimated
An ecologically and culturally significant fish passage project in the US state of Washington would restore access to 719.4km2 of lake habitat and 47.3km of riverine habitat, which has been inaccessible for anadromous and resident salmonids over the past 100 years. The project is being planned for Cle Elum Dam in the Yakima river basin and involves the US Bureau of Reclamation (USBR), Washington State Department of Ecology (Ecology), Washington State Department of Fish and Wildlife (WDFW) and the Yakama Nation. The project has two components—fish passage facilities design, with Reclamation taking the lead, and a fish reintroduction programme developed by the Yakama Nation with assistance from WDFW.
In 1907, USBR constructed a temporary rock-filled crib dam on the outlet of historic Lake Cle Elum to provide an additional 32m3x106 of irrigation water storage. This was followed by completion of Cle Elum Dam in 1933 on the Cle Elum River, which increased storage capacity to 538m3x106. The dam is a zoned earthfill design with a structural height of 50m and a crest length of 549m. Its maximum pool elevation is 683m and the spillway crest is at elevation 678m. Neither facility was constructed with allowance for upstream or downstream fish passage, resulting in the extirpation of anadromous salmon and steelhead populations in the upper Cle Elum subbasin.
Historically, tens of thousands of sockeye, coho, and spring Chinook salmon and steelhead returned annually to spawn in Lake Cle Elum and its upstream tributaries. The annual return of salmon was an important source of marine-derived nutrients that helped maintain ecosystem health in the upper Cle Elum River sub-basin. Fishing encampments were established by people of the Yakama Nation at both the inlet and outlet of the lake and it was here that the Yakama people harvested and dried primarily sockeye salmon to sustain them during the winter months and to trade with coastal tribes in the Puget Sound region.
In 2002, as part of a mitigation agreement with the WDFW and a settlement agreement with the Yakama Nation, the Yakima Dam Fish Passage Study was initiated and the Technical Yakima Basin Storage Fish Passage Workgroup (Core Team) was formed and charged with studying the feasibility of providing fish passage at Cle Elum and four other USBR storage dams in the Yakima River basin (Keechelus, Kachess, Bumping, and Tieton).
During development of the Phase I Assessment (USBR 2005), the Core Team evaluated a range of conceptual designs for upstream and downstream fish passage at each of the five dams. Design concepts took into consideration the following physical, operational, and biological elements:
• Below-freezing air temperatures in the winter.
• Excessive snowfall and snow depth during the winter.
• Partial- to complete-reservoir water surface freezing over during the winter.
• Wide range of fluctuation in reservoir water surface elevation.
• Proposed fish passage facilities could not impact the total water supply available or the timing or quantity of irrigation water deliveries for Yakima project water users.
• Peak anadromous salmonid smolt outmigration period is 15 March to 30 June.
• Peak anadromous salmonid fall juvenile outmigration period is September through November.
• Peak adult anadromous salmonid upmigration period is April through December.
• Behaviorally, salmonid smolts are attracted to surface spill and prefer to migrate in the upper 3m of the water column.
• Adult and juvenile salmonids require adequate attraction flow for successful migration.
The Core Team also considered the biological benefits in terms of the quantity and quality of habitat that would be made available by providing fish passage at each of the five USBR dams. By considering the estimated costs and biological benefits of each conceptual design, the Core Team determined the unit cost per riverine habitat river mile for each design concept for each dam. Cle Elum and Tieton dams tied for the lowest estimated unit cost, but Cle Elum was given preference because:
• Adding fish passage to Tieton dam would be more complicated and likely to be more costly than Cle Elum, due to its location in a narrow, deep rock canyon.
• There was considerably more biological and habitat information available from research previously conducted by the National Marine Fisheries Service in the late 1990s (Flagg, et al 2000) on the Cle Elum subbasin in relation to restoring sockeye salmon.
A multilevel intake structure was the Core Team’s preferred conceptual design for downstream passage and a conventional trap-and-haul facility for upstream passage. The main features of the downstream passage facilities included a multilevel intake structure located in the forebay, an access bridge to the multilevel intake structure and a juvenile fish bypass conduit. Upstream fish passage facilities included a barrier-guidance dam, fish ladder and adult collection facility. Reclamation convened a Value Planning Team comprised of members with engineering, geology, and biology backgrounds from multiple agencies to take a fresh look at the original conceptual design and look for alternative ways to provide fish passage or enhance the original design. The team suggested modifications to the original design (USBR 2009) including: eliminating the access bridge and barrier-guidance dam; relocating the multilevel intake structure against the right abutment; and relocating the adult fish ladder and adult collect facility from the left to the right stream bank.
These modifications resulted in significant cost savings while maintaining the desired operational and biological objectives, and were approved by the Core Team resulting in the preferred alternative (see figure 3) [Presented in the Cle Elum Dam Fish Passage Facilities and Fish Reintroduction Project Final Environmental Impact Statement (FEIS) (Reclamation and Ecology, 2011) (http://www.usbr.gov/pn/programs/eis/cle-elum/index.html).]
The multilevel intake structure (figure 4) consists of five 3m x 6m gate openings located vertically every 3m to provide a surface water spill route for outmigrating fish over a 15m fluctuation in reservoir water surface elevation (between 668m and 683m [full pool]). The footprint of the structure is 49m long by 28m wide, with a height of 17.9m. The juvenile fish bypass conduit consists of a 2m diameter, non-pressurised, reinforced concrete conduit that extends 290m from the base of the intake tower through the right abutment that will discharge fish into the stilling basin at the base of the spillway. A key advantage of this design is that it will provide for 100% passage during the March 15-June 30 smolt outmigration period at both the 50th and 75th-percentile reservoir water surface elevations, and for 61% passage at the 25th-percentile reservoir water surface elevation, based on the 1981-2003 period of record.
A fish ladder is used to volitionally move upstream migrants from the river into the trap. The fish ladder for upstream passage consists of a series of 12 pool-steps, 2.4m long by 1.2m wide by 1.2m deep. The ladder exits into the trap entry area where fish will be held and then moved using a fish lock and flume system to a wet room where bio-sampling will occur before being transported and released upstream of the dam. Four 200hp pumps will be used to provide flow to the fish facility and fish ladder and to provide additional attraction flow as needed.
Fish reintroduction programme
The second component of this project was to determine the feasibility of fish reintroduction. In 2005, the Yakama Nation Fisheries Resource Management Programme (YNFRMP) initiated a reintroduction study using juvenile coho salmon and adult sockeye salmon. For this study, a temporary interim wooden flume designed for up to 400cfs of flow was installed on the existing concrete spillway of the dam. The purpose of the coho introduction was two-fold: to test the ability of fish to use the interim passage facilities; and to improve the health of the ecosystem for salmon by introducing marine-derived nutrients above the dam (from carcasses of returning fish).
Results proved favorable for successfully passing coho smolts and, in 2009 and 2010, the YNFRMP reintroduced 1000 and 2500 adult sockeye salmon, respectively, into Lake Cle Elum. This spring, an estimated 80,000 sockeye smolts successfully outmigrated past Cle Elum dam using the interim wooden flume and have been detected at the Chandler Juvenile Collection Facility in the lower Yakima River.
The limitation of this interim passage facility is that it is operable only when the reservoir water surface elevation is above the spillway (678m). For the smolt outmigration period of 15 March to 30 June, the 25th percentile reservoir pool elevation provides surface spill for 24% of this time period (6/3 to 6/28); the 50th-percentile reservoir level provides surface spill 43% of the time (5/16 to 6/15); and the 75th-percentile reservoir level provides surface spill 65% of the time (4/22 to 6/30), based on the 1981 2003 period of record.
For many of the natural resource professionals who have dedicated their working careers to improving existing and reestablishing extirpated anadromous and resident salmonid populations in the Yakima Basin, the prospect of providing fish passage at Cle Elum is met with much enthusiasm. While the total construction cost for the preferred alternative is estimated at US$84M (2008 dollars), the ecological and social benefits of reconnecting the upper Cle Elum subbasin to the rest of the Yakima Basin cannot be underestimated.
The next steps in the planning process are to conduct hydraulic modelling of the preferred alternative for both upstream and downstream facilities and to collect geotechnical data for the final design of the intake structure and juvenile fish bypass conduit through the right abutment.
Joel Hubble, US Bureau of Reclamation Fishery Biologist, Pacific Northwest Region. Editing by Lynn Holt, Reclamation Technical Writer, Pacific Northwest Region