DESCRIPTION
We propose to use SRFB funds to develop a preliminary restoration design and acquire construction permits for lower Crescent Harbor Creek, a tributary to the Crescent Harbor Salt Marsh restoration site on northern Whidbey Island. The project is intended to restore the historic floodplain alignment, reduce stream velocity to increase fish access and improve water quality, and restore native wetland hydrology in lower Crescent Harbor Creek. Goals for the project are to: 1. Sustainably restore natural stream and floodplain processes, conditions, functions, and biological responses 2. Restore riparian and scrub-shrub wetland habitats 3. Restore non-natal stream channel rearing capacity and freshwater nearshore inputs for ESA-listed juvenile Chinook salmon during the early phases of their oceanward migration 4. Restore channel spawning habitat capacity for adult coho salmon 5. Restore estuarine and wetland habitat conditions for other native fish and wildlfe species 6. Improve water quality conditions within lower Crescent Harbor Creek and the Crescent Harbor Salt Marsh, a 206 acre SRFB- and ESRP-funded estuary restoration site located at the mouth of Crescent Creek. Matching funds, in the form of staff time for design review and for securing the permits necessary for project construction, will be provided by the US Navy.
SRFB funds were used to complete a preliminary restoration design for Crescent Harbor Creek, including a design report and a detailed plan set. SRSC hired project engineer Paul Tappel of Fisheries Engineers, Inc to complete the work. Design work began with detailed site surveys to collect information on site topography and features using a total station and other survey equipment. Data collected included natural slope contours and topography, alignment and grade for the existing ditched creek channel, dimensions and elevations for the existing culvert, streambank and streambed characteristics. Additionally, rainfall and basin size data were used to estimate low fish passage flow, high fish passage flow, and 100 year flood flows for Crescent Harbor Creek.
These data were used to develop a design for a gradually meandering channel that roughly follows the historic alignment of Crescent Harbor Creek between Crescent Harbor Road and the estuary at the creek mouth. The existing ditched channel is about 1,000 feet long with an overall slope of 1.4%. The design channel is 1,420 feet long, with riffle slopes varying from 1% to 4%, and with pool depths varying from 2-4 feet. The design calls for a roughened boulder channel for 40 feet below the culvert as a means of maintaining fish passage through the moderately undersized (though passable) culvert. Channel slopes in this reach were adjusted to eliminate any potential backwater effects. Below this reach, rootwad and log placements were included in the design to increase in-stream habitat diversity and complexity, and scissor log weirs were included just upstream of pools to increase pool-maintaining velocities during high flows. The stream channel alignment will bypass an existing anthopogenic wetland created by a low berm crossing the historic channel alignment in order to avoid adverse impacts to wetland vegetation and aquatic life. The existing wetland does not appear to receive flow from the ditch, and the design channel would not discharge into the wetland. The design report includes construction cost and materials quantity estimates. Environmental staff from Naval Air Station Whidbey Island have reviewed and approved the preliminary design.
The original scope of work to complete a prelminary design was completed under budget and the sponsor completed the final designs for the restoration preferred alternative.
