Streamflow Hydraulics of a Sheefish Spawning Reach of the Selawik River, Alaska - Jeff Conaway , U.S. Geological Survey (co-authors: Christian Zimmerman, U.S. Geological Survey)

ABSTRACT

The Selawik River is a Wild and Scenic River within the Selawik National Wildlife Refuge in Northwest Alaska. The river flows approximately 300 km through a wide tundra valley and meanders most of this length. The river is a key spawning location for Sheefish, an important subsistence resource in the Kotzebue region, where over 20,000 fish are harvested annually. The largest retrogressive thaw slump in Alaska was identified on the upper river in 2004. This thermokarst feature is located approximately 40 km upstream of spawning areas and is contributing increased sediment to the river. Quantifying streamflow hydraulics and sediment transport potential is one component in evaluating the potential impact of increased sediment on spawning habitat and incubating eggs. In September 2009, an acoustic Doppler current profiler was used to map depths and multi-dimensional velocities in a200 m long linear pool where spawning occurred in 2008. Average measured velocity was 0.8 m/s and the highest measured velocity was 1.5 m/s at a discharge of 10.4 m3/s. Average flow depth was 0.5 m and the maximum flow depth was 1.4 m. Velocity vectors were generally aligned with the direction of flow for the entire reach. The intent of this study was to pair measurements of streamflow hydraulics with spawning activity, but spawning did not occur during our field visit. We compared our data to a 2008 survey of eggs in this reach. Locations with 10 or more eggs were in areas with flow depths between 0.55 to 0.94 m and flow velocities between 0.60 and 0.95 m/s. The highest concentration of eggs occurred in locations immediately downstream of areas of high velocity and in the center of the channel. This indicates spawning took place in the high velocity areas and the eggs then settled out of suspension downstream. Our data indicate that the highest concentrations of eggs are in the center of the channel of linear reaches that are bounded by riffles.

Topic: Alaska Hydrology