Presentation Type

Presentation - Campus Access Only

Faculty Mentor’s Full Name

George Furniss

Faculty Mentor’s Department

Bitterroot College

Abstract

The Bitterroot River is a fast moving cobble-gravel-sand-bed, braided and meandering, north flowing river with peak discharges above ten thousand cubic feet per second during spring snow melt at our riverbank community, Hamilton, Montana. The river is the life blood of our valley with water quality good enough to support trout. Low flow of August can drop to 500 cubic feet per second at Hamilton endangering trout with high temperatures, were it not for the cooling effect of groundwater seeping into the channel and shade from trees.

We examine a ten mile reach between Anglers Roost and Woodside Crossing where there is heavy visible interference from man-caused armoring (riprap) of the banks to protect bridges, roads, homes, and irrigation diversion dams or jetties. Here the river descends at a rate of 15 to 17 feet per mile occasionally widening its active channel to half a mile and then coalescing to a single channel where confined by structures.

Our hypothesis is that increasing percentages of riprap control the movement of the channel because energy of peak flow increases when the river is constrained. Even small reaches of the river can change dynamically as illustrated by two separate meander cutoffs through 18 years. We illustrate major channel changes by comparing main channels between 1995 and 2018.

Category

Physical Sciences

Share

COinS
 
Apr 27th, 9:40 AM Apr 27th, 10:00 AM

Time Comparisons of Channel Lines of the Bitterroot River

UC 330

The Bitterroot River is a fast moving cobble-gravel-sand-bed, braided and meandering, north flowing river with peak discharges above ten thousand cubic feet per second during spring snow melt at our riverbank community, Hamilton, Montana. The river is the life blood of our valley with water quality good enough to support trout. Low flow of August can drop to 500 cubic feet per second at Hamilton endangering trout with high temperatures, were it not for the cooling effect of groundwater seeping into the channel and shade from trees.

We examine a ten mile reach between Anglers Roost and Woodside Crossing where there is heavy visible interference from man-caused armoring (riprap) of the banks to protect bridges, roads, homes, and irrigation diversion dams or jetties. Here the river descends at a rate of 15 to 17 feet per mile occasionally widening its active channel to half a mile and then coalescing to a single channel where confined by structures.

Our hypothesis is that increasing percentages of riprap control the movement of the channel because energy of peak flow increases when the river is constrained. Even small reaches of the river can change dynamically as illustrated by two separate meander cutoffs through 18 years. We illustrate major channel changes by comparing main channels between 1995 and 2018.