Chehalis Basin flood authority outlines local projects, introduces flow‑through flood control concept

The Chehalis River Basin Flood Authority told Thurston County commissioners on July 16 that a mix of local projects, a basin warning system and a proposed “flow‑through” flood control facility together form the basin’s current strategy for reducing flood hazard and protecting aquatic species.

The authority’s staff member Scott Boettcher summarized the authority’s work, saying the body was created after the February 2007 storm that caused about $900 million in damage and that the local projects program has completed roughly 150 projects since 2012 and spent about $90 million, primarily on community‑level flood protection.

Boettcher and Vicki Raines, chair of the Flood Authority, described types of projects funded: small structural measures such as grassy swales (costs cited at about $400,000–$500,000 for one project protecting a wastewater treatment plant), pump station and levee work at Chehalis‑Centralia Airport (about $2.3 million), engineered log structures to protect the Montecena wastewater plant (about $2 million), and home‑level measures such as retrofitted flood vents (average cost cited $8,000 per home, with an average quoted reduction in flood insurance premiums of about 50 percent for participating homes).

Boettcher described the authority’s flood‑warning system, which uses about 14 river gauges and sends email alerts when water levels hit trigger thresholds set roughly one to two feet below technical flood stage. The authority said annual operational costs for the warning system are about $100,000–$110,000 and that the service averages about $26 per registered user when the subscriber base is counted.

The presentation included a four‑minute explanatory video on a proposed “flow‑through” flood control facility (referred to in the briefing as the FRE or flow‑through dam). The video and presenters said the structure is designed to allow near‑normal river flow and volitional fish passage in ordinary conditions and to hold back water only in extreme, rare flood events. Presenters said, based on modeling, the facility would have operated only three times in the last 20 years but would have materially reduced downstream damages and I‑5 closures during major events.

Boettcher and Raines said the proposal is one option among multiple packages the Office of Chehalis Basin and the flood control zone district are evaluating; those packages include combinations of the flow‑through facility, land‑based alternatives (levees, conveyance work, buyouts, property elevation) and other projects. They said the decision path includes a draft environmental impact statement (EIS) and NEPA review that will better define environmental tradeoffs, construction staging and effects both upstream and downstream.

Presenters emphasized tribal involvement and that both the Quinault Indian Nation and the Chehalis Confederated Tribes have representatives on the basin board and have, to date, supported further study of the flow‑through concept while asking for additional science. Presenters also said funding since 2016 has come largely through state appropriations via the Office of Chehalis Basin and that a federal BRIC grant reduction has put some lower‑basin projects at risk.

Commissioners asked about upstream ecological effects if water were intentionally held behind the structure during extreme events, how the EIS will study impacts to timber and habitat, and how packages compare when land‑based measures are combined with or substituted for the retention facility. Flood Authority staff said the draft EIS is intended to identify locations and magnitudes of impacts and that alignment changes and mitigation measures have already been adjusted during draft EIS work.

The Flood Authority requested that commissioners consider a previously circulated resolution of support for the basin process; Boettcher said the resolution asks local governments to support continued evaluation, including the flow‑through facility among other alternatives. No formal county action on the resolution was taken during the work session.