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Hawk Creek Fishway ProjectPROJECT GOALRestore adult and juvenile salmonid passage to 1.5 miles of spawning and rearing habitat during all flows. TARGET SPECIESOregon Coast Coho Salmon PROJECT BACKGROUNDThe Neskowin Regional Water District Treatment Plant  Click photo to enlarge Draining 5.8 square miles and flowing through private forest land, a golf course, and a residential area, Hawk Creek flows into the mouth of Neskowin Creek just before it drains into the Pacific Ocean in Neskowin, Oregon. In 1980, the Neskowin Regional Water District (NRWD) constructed a water treatment plant adjacent to Hawk Creek at river mile 1.1. The NRWD's water right allows the withdrawal of up to 0.65 cfs from Hawk Creek to supply municipal drinking water for the Neskowin area. Along with the plant, the NRWD constructed a water intake to divert water from Hawk Creek, and a 4 foot rock weir (25 feet downstream of the water intake) for impounding water. The rock weir impoundment controls the water surface profile at the intake structure, but is also a flow-dependent passage barrier, blocking 1.5 miles of salmon spawning and rearing habitat. In January 2001, the NRWD installed a Sure-flow (Model# SCS6) rotating self-cleaning drum screen to update the intake for compliance with Oregon Department of Fish and Wildlife (ODFW) Fish Screening Criteria. The current water diversion system includes the 4 foot rock weir, upstream pool, and the Sure-flow fish screen on the end of a cement intake structure. Fish Utilization Coho, winter steelhead, and cutthroat trout are present throughout the Hawk Creek basin. Upstream of the impoundment there is 1.5 miles of fish use. Coho and steelhead utilized 0.7 miles, which is verified by the NNWC Rapid Bio-Assessment Final Report (2004), and cutthroat utilize an additional 0.8 miles of habitat. Chum occupy the lower half mile of Hawk Creek and have not been observed above the treatment plant. Habitat Characterization  Temporary weirs and water impoundment impede adult and juvenile passage at varying flows. Habitat in the lower Neskowin watershed has been severely altered due to golf course and residential developments. It is critical that fish have access to upstream spawning and rearing areas. A 1994 ODFW habitat survey from the treatment plant upstream characterizes the substrates as a mix of gravels (40%), cobbles (26%), and fines (23%). The stream gradient averages 4.9% and the units are rapids (69%) and pools (9%). In 2007, TEP and ODFW walked the reach upstream of the treatment plant and found the 1994 survey data to represent current conditions. One exception however, is the increased beaver activity that has enhanced the salmon rearing areas. The undisturbed riparian and adjacent upland areas are comprised of a mixed alder-conifer forest, with some of the conifers reaching 1-3 feet in diameter. These areas offer a good source of future large wood recruitment to the stream channel. Several trees blown down during wind storms lie in the upland areas. The closed riparian canopy contributes to summer water temperatures that average 54°F. Project Initiation While ODFW visited the plant to assist with the screening updates, they suggested that the NRWD pursue funding through ODFW's Fish Screening and Passage Program (FSPP) to address fish passage issues at the weir. Surplus funding became available through the FSPP to assist the NRWD in temporarily addressing fish passage problems until a permanent solution could be implemented. In June 2005, the ODFW and NRWD installed two temporary rock weirs below the water impoundment to facilitate adult fish passage. However, during low flows (1-2 cfs), no water flows over the top of the weirs. Although adult passage is possible at flows greater than 10-15 cfs (November through April), the weirs were only intended for temporary passage and they are not keyed into bank. The temporary weirs and impoundment weir will be removed prior to installation of the permanent fishway. In Spring 2006, TEP received funding through the FSPP to hire a consultant to design a fishway that would provide adult and juvenile fish passage at low flows. TEP matched the FSPP award with internal TEP funds. The engineering is complete and approved by the local ODFW biologists and ODFW's FSPP engineers. PROJECT DESIGN - 170' Meandering Channel - 16 Notched Concrete Sills - Large Woody Debris & Boulders - Fishway Design Criteria  Treatment plant, water intake, and water impoundment. Development of the conceptual design alternatives for fish passage at the Hawk Creek diversion involved the identification of design criteria. While upstream adult passage may be the more obvious passage requirement, juvenile passage is also important as it allows juvenile fish to migrate upstream and downstream to find suitable rearing habitat throughout the year. The primary NOAA and ODFW design criteria for the Hawk Creek fishway are shown below. Fishway improvements at the Hawk Creek project site must provide both upstream and downstream passage for both adult and juvenile fish during their periods of utilization within Hawk Creek. This criterion ensures fish have unrestricted access to all parts of Hawk Creek while utilizing the creek. Maximum step height in the fishway must not exceed 0.5 feet to accommodate juvenile fish passage. This criterion must be incorporated into this project to secure permit approval from state and federal agencies. Upstream and downstream passage must be provided at flows ranging between 1 and 96 cubic feet per second, or 95% exceedance. This criterion is also part of the state and federal passage guidelines that must be incorporated into the project. These criteria made finding a solution challenging, since there was a total channel drop of 8 feet through a 170 foot reach. Adhering to the fish passage criteria led to the design discussed below. Concrete Sill Layout The total elevation change in the existing stream channel, from the crest of the existing diversion structure to the bed of the stream channel downstream of the existing passage sills, equals 8 feet. Using the 0.5 feet maximum differential between sills for juvenile fish passage resulted in the need for 16 concrete sills to be installed in the project reach. Spacing between the concrete sills will equal approximately 10 feet so the channel through the sill reach meets the existing channel grade approximately 170 feet downstream of the existing diversion structure. The concrete sills should last over 50 years. Concrete Sill Notches Notches installed in the concrete sills will be designed to confine the stream flows anticipated during summer low flow periods for juvenile passage. The depth of the notches will be 0.5 feet below the crest of the concrete sill on either side of the notch. These notches are designed to pass 5 cubic feet per second when the notches are flowing full. At flows greater than 5 cubic feet per second, water will begin flowing over the sills on either side of the notch with the dominant flow passing through the notch. Upstream migrating fish will sense this dominant flow and swim upstream within this flow region. Concrete Sill Notch Shape The shape of the concrete sill notch will vary depending on the location of the notch within the channel. Notches on the outside of a bend will have a steep-sloped outer edge with a flat center section and a gentle-sloped inner edge. In transition sections, the notch will have an intermediate sloped edge on both sides of a flat bottom. These differing notch shapes were designed to mimic natural channel shapes as they move through different reaches of the stream. Concrete Sill Notch Location Location of the notch within the concrete sill will depend on the proposed location of the channel thalweg within the new channel section. Several slight bends will be incorporated into the new channel section to create fish habitat features within this reach. As the channel thalweg shifts from side to side in the new channel, the location of the notch will move to different locations on the concrete sills. Low Flow Notch Additional discussions with ODFW resulted in the addition of a low flow notch in the bottom of the concrete notch. This notch will be 1 foot wide by 3 inches deep and installed in the flat section of the sill notch. This notch was added to ensure juvenile passage at low flows. Stream Gravel Installation After all of the concrete sills are installed, a stream gravel mix will be added to raise the level of the rebuilt channel to the top of the downstream concrete sill. This gravel mixture will be composed of fines, sand, gravel, and small cobble to match the stream bed materials currently found in the Hawk Creek stream channel. Installation of this material will help to stabilize the concrete sills and will form the new channel in the rebuilt channel reach. Installation of Large Woody Debris & Boulders Up to 30 logs (10 with rootwads, 20 without) will be installed between the concrete sills to develop fish habitat features in the rebuilt channel reach. Log lengths will average 20-24 feet long for rootwad logs and 30 feet for logs without wads. Minimum diameter for all logs will be 16-24 inches. Logs will be installed by burying ends in the installed gravel material between the concrete sills and/or wedging between 2-4 foot boulders below the surface of the new stream channel. COSTProject Management & Planning: $23,000 SCHEDULEDesign & Engineering: Completed PARTNERSTillamook Estuaries Partnership: lead project manager, partner coordination, grant management, engineering funds |
