Akpelik Creek demonstrates the significant influence tributaries have on the structure of the Kobuk River and their ability to add complexity and unique habitat to the main channel. Akpelik Creek also contrasts the Kobuk with its presence of large woody debris that plays a role in the structure of its channel compared to the very local influence large woody debris seems to have in the main channel of the Kobuk River.
Akpelik Creek is a cold water tributary from the north entering the main channel of the Kobuk River with a gravel point bar and backwater just upstream of the confluence, creating a great spawning site for Chum salmon. The tributary enters river right of one of
the right branches of the main channel and has a roughly estimated flow of ~10 cfs. The gravel bar downstream of the confluence is mostly cobble with some gravel, characterized by large mounds of substrate disturbed by ice scour. It also has lobes created by flow and deposition of the tributary. Vegetation is a mix of Willow and Cottonwood/Black Spruce forest along the gravel bar. Small seedlings are popping up on the gravel bar and there are a few isolated pieces of large woody debris.
The Kobuk at this location has several large channels with islands covered by Willow and Black Spruce vegetation.
The tributary itself is a braided channel with cobble substrate at the mouth and mostly a mix of gravel and pebble just upstream of where it joins the Kobuk. Ripples where the creek enters the main channel are a mix of gravel with some small cobbles and a little sand with periphyton covering the substrate. Large woody debris is present perpendicular to flow and significant riparian overhang defines this well developed channel. Riparian anchoring stabilizes the bank creating a “levy” (~2 meters high) separating the calm backwater of the Kobuk’s main channel from the tributary channel. A portion of the creek flows into the backwater zone. Riparian vegetation grows close to the edge of the backwater and is a diverse mix of grasses, Willow, Cottonwood, and mature White Spruce. Water chemistry of the tributary is not very different from that of the Kobuk having a little lower acidity and temperature but similar nutrient levels.
Another small tributary enters the backwater upstream of the creek confluence. This inflow is extremely productive, with lots of algae. In looking at aerial photographs, it appears to be a separate drainage system from Akpelik Creek.
The deposition and flow of this tributary creates a surprising and unusual feature in the Kobuk main channel. It’s a bit of a mystery: why is this backwater here with a large gravel bar on the outside of the meander? The backwater is right where a cutbank would usually be- on the outside of a large meander bend. Deposition by the tributary appears to create the calm, shallow backwater zone and ~200 m of gravel deposited on the outside of the meander. This creates an excellent place for Chum to spawn. 14 redds were counted in the upper part of the backwater area. Lots of wolf and Grizzly tracks in this area suggest they in turn take advantage of this backwater area as an abundant food source.
Akpelik Creek has a distinct and significant impact on the structure of the Kobuk River and helps create seemingly ideal conditions for chum to spawn in this location. The influence of each tributary on the local geomorphology as it enters the main river is unique, but this was an especially incredible site to watch spawning salmon brave the shallow ripples to reach the deeper pool where the females defensively guard their redds.