If you have questions about this project, email staff engineer Shaun Honeycutt of Chelan County Public Works. Or call the department at 509-667-6415.
Twenty-Five Mile Creek Culvert Replacement
Project Update
RFQs Due Jan. 17, 2025: Consulting firms with expertise in the areas of structural/civil engineering design, geotechnical, hydraulic, environmental documentation, appraisal services, and construction management are invited to submit their qualifications for developing the Twenty-Five Mile Creek Culvert Replacement Project, Phase 1. The project proposes replacing a dual box culvert with a new bridge to allow post-fire flood flow to pass under South Lakeshore Road in Chelan, Wash. Phase 1, the design phase, is estimated to start in February 2025 and be complete by May 2026.
Project Description & Benefits
The project site is about 20 miles northwest of Chelan, Wash., where South Lakeshore Road crosses Twenty-Five Mile Creek. This roadway is the only north-south corridor for residents and emergency responders along the west side of Lake Chelan, one of the most popular tourist destinations in the state. South Lakeshore Road is a 35-foot-wide, two-lane road that has an average daily traffic count of more than 200 vehicles.
The creek passes under the road through a double-barrel concrete box culvert that is 50 feet long and consists of two 8-foot-wide by 6-foot-high barrels. Existing utilities, including power and phone, are overhead.
To reduce damage and traffic delays from post-wildfire debris flows created by the 2021 Twenty-Five Mile Fire, Chelan County will replace the dual box culvert with a concrete bridge that spans the creek, allowing post-fire flood flow to pass under South Lakeshore Road, not over it.
The new bridge is expected to provide 12-foot-wide lanes with 7-foot-wide shoulders (38 feet curb to curb) to match adjacent roadway geometry east of the Twenty-Five Mile State Park entrance. The bridge length will allow for post-fire flood and debris flows to pass while also providing fish passage during all state-required fish passage flows. In addition, barrier heights shall be sufficient to protect bicycles using either a single-barrier system or a combination of concrete barriers with metal railing added to the top.
History
The Twenty-Five Mile Creek drainage consists of 41.8 square miles of steeply sloping terrain within the Wenatchee National Forest. Watershed elevations range from about 7,200 feet at the creek headwaters to less than 1,140 feet at the culvert crossing. The creek flows in generally a northeasterly direction, flowing through Twenty-Five Mile State Park and reaching Lake Chelan, about 1,000 feet after passing under South Lakeshore Road.
Twenty-Five Mile Creek hosts several fish species, including westslope cutthroat trout, stocked rainbow trout, kokanee salmon, eastern brook trout and suckers. The current box culvert is a partial barrier to fish passage at certain times of the year.
The Twenty-Five Mile Fire was first reported on Aug. 15, 2021, and burned about 22,217 acres – almost all of which (79 percent) is within the 26,997-acre watershed. Based on a rapid scientific and engineering assessment of the area burned by the fire, it was determined 83 percent of the burned area has a moderate or high runoff potential. The assessment identified imminent threats to values at risk/critical infrastructure, including the Twenty-Five Mile culvert. It details a future concern for roads, culverts, bridges and channels along the drainage paths of the burned watersheds in that they may be plugged, overtopped or washed away more frequently than experienced under pre-fire conditions.
As a result, the National Resource Conservation Service conducted a pre- versus post-fire hydraulic analysis/ The analysis shows that at the county’s South Lakeshore Road culvert, Twenty-Five Mile Creek may witness a six-time increase in runoff as a result of post-fire conditions (680 cubic feet per second pre-fire versus 4,000 cfs post-fire).
If this were to occur, the culvert will be at capacity, causing the creek to flow over the top of South Lakeshore Road. In all likelihood, the road will be washed out and the state park campground below the roadway will be inundated with water.
Project Schedule
Phase I of the project, the design phase, is underway, with requests for qualifications now out for interested consultants. Design is estimated to start in February 2025 and be complete by May 2026. Construction is planned for summer 2027.
Funding
The project is jointly funded between the Chelan County Flood Control Zone District and Chelan County Public Works. FEMA has awarded the project a grant for design and construction.
Receive Project Updates
Project updates, when they are available, will be posted to this webpage. Or subscribe to the Chelan County e-newsletter. Updates also will be posted to the Public Works Facebook page.
Posted: 12/05/2024 11:51 AM
Last Updated: 12/09/2024 10:59 AM
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The information contained on this site is provided as a courtesy of the Chelan County. Where it exists, the "Index.txt" will contain a brief explanation of files contained in this folder
Chelan County makes every effort to ensure the accuracy of the information provided on its web site. However, due to the possibility of transmission errors, HTML browser capabilities, changes made since the last update to the site, etc., neither Chelan County, nor any agency, officer or employee of Chelan County warrants the accuracy, reliability, or timeliness of any information published by this system and shall not be held liable for any losses caused by reliance on the accuracy, reliability, or timeliness of such information. Portions of such information may be incorrect or not current. Any person or entity that relies on any information obtained from this system does so at his or her own risk.
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