Streamwise Velocity, Cross-section Bathymetry, and Substrate Particle-size Distribution and Loss on Ignition at Bull Trout (Salvelinus confluentus) Spawning Habitat in the Cedar River Municipal Watershed, Washington

The upper Cedar River Municipal Watershed (CRMW) is managed by Seattle Public Utilities and provides habitat that sustains an isolated adfluvial population of Endangered Species Act-listed bull trout (Salvelinus confluentus). Bull trout spawning in the CRMW begins in early fall when the water surface elevation of Chester Morse Lake and the stream discharges in its major tributaries, the Cedar and Rex Rivers, are at their annual lows. As obligatory stream spawners, bull trout primarily spawn in pool-riffle habitats within the Cedar River’s inundation zone. Subsequent increases in reservoir elevation inundate these areas, transforming them into lentic habitats.

Reduced stream velocity within the inundation zone of the Cedar River may decrease interstitial flow and dissolved oxygen concentrations within bull trout redds, potentially affecting the development and survival of incubating embryos. Fluctuations in reservoir elevation associated with high-streamflow events, combined with increased sediment transport and deposition, may further reduce interstitial flow through redds and exacerbate the effects of reduced water exchange on incubating embryos.

To better understand the potential impacts of habitat modification and sedimentation on bull trout, the U.S. Geological Survey (USGS) Washington Water Science Center conducted bathymetric, velocimetric, and sediment-characterization surveys in spawning habitats along the lower Cedar River upstream from Chester Morse Lake between March and December 2025. Five survey sites were located within the inundation zone of the Cedar River and four additional sites were located farther upstream in areas unaffected by reservoir operations. Seattle Public Utilities also performed sediment characterization surveys at two of these sites during June and September 2024. Data from these bathymetric, velocimetric, and sediment characterization surveys are presented here as comma-separated values (.csv) and image (.jpg) files.