Regulated scouring in a sand-bed river for channel habitat maintenance: A Platte River waterfowl case study

The planned Narrows Reservoir on the South Platte River in Colorado is expected to jeopardize the maintenance of scarce instream waterfowl habitat 400 km downstream in Nebraska's Big Bend reach of the mainstem Platte River. Extreme shrinkage of wide, shallow channel habitat for sandhill and endangered whooping cranes in the Central Flyway has resulted from past reservoir development along the North and South Platte Rivers in Wyoming and Colorado. Proposals to counteract further shrinkage caused by streamflow regulation and depletion include controlled annual peak flows designed to scour the banks, sandbars, and emerging vegetation. The criteria for effective channel maintenance by streambed scouring are examined, as well as the principles involved. The feasibility of preserving the remaining habitat by releasing scouring flows from the Narrows Dam is found seriously lacking. Alternative mechanical measures, such as dredging the channel and bulldozing the tree cover, may prove more practical, although possibly unaffordable.