Fan-eddy complex, simplified
The fan-eddy complex is a sequence that helps give the Colorado River its “river profile” of calm pools of water upstream piled behind a rapid, which gives way to a complex flow zone downstream with side eddies and gravel bars. That combination helps create ecological niches in the canyon for native fish and other species.
Now that Glen Canyon Dam prevents most sediment from naturally moving down the main stem, the Colorado River’s hundreds of tributaries are largely responsible for moving sediment and big boulders into the river.
“The fan-eddy complex creates sandbars and a network of pockets where fish and bugs can hang out,” Sarah says. “These debris fans are creating their habitat. The river may be too cold for some species, but the sandbar is like a fish nursery there.”
Unkar Delta overlook
We arrive at the Unkar Delta overlook and it is, as advertised, stunning. We stand on red cliffs rising dramatically over the river, which wraps around the delta in a hairpin curve.
Erin Sattherwaite, a marine ecology graduate student, takes in the view of the
Unkar Delta overlook. Photo: Joe Proudman/UC Davis
The Unkar Delta was formed by rock debris carried from the Grand Canyon’s North Rim by Unkar Creek. The plain stretches out broadly, and we spot rectangular outlines of rocks, the remnants of dwellings used by ancestral Puebloans. They lived and farmed in the area from about A.D. 850 to 1200, planting corn, squash and beans on irrigated fields and terraces near the river and creek.
The students are introspective, finding ledges and nooks where they can sit, stare and absorb. There’s the beauty in front of us, the remnants of human and natural history below and around us, and there’s Unkar Rapid, burbling just around the curve. It’s one of a handful of rapids we have left on this trip and a reminder that our time will soon draw to a close.
Graduate student Michael Kenney points out the Great Unconformity. - Credit: Mille Levin / UC Davis