Earth and Planetary Sciences ETDs

Publication Date

7-1-2011

Abstract

Beaver damming in streams is thought to increase bed elevation through in-channel sediment storage, thus beaver reintroductions are used as a river restoration tool to repair incised stream channels. However, effects of beaver damming are dependent on specific stream hydrologic and geomorphic characteristics. Data on dam effects, especially the longevity of dam effects, are limited. To investigate whether damming promotes channel aggradation and creates persistent geomorphic change, 9 reaches containing 46 cross-sections were studied on Odell Creek at Red Rock Lakes National Wildlife Refuge, Centennial Valley, Montana. Odell Creek has a basin area of 46 km2, a snowmelt-dominated hydrograph and peak flows between 2 - 10 m3s-1. Odell Creek flows down a fan with a decreasing gradient (0.018–0.004), terminating in Lower Red Rock Lake as a mostly single-thread, variably sinuous channel, except where beaver damming has caused overbank flooding, creating multi-thread channels. The study reaches represent downstream variability including non-dammed sites and beaver dams built and abandoned over the last decade. In-channel sediment characteristics and storage were investigated using pebble counts, fine sediment surveys, sediment mapping and one dam breach survey. Volumes of fine sediment (≤ 2 mm) stored behind beaver dams range from 40 – 463 m3. Deposition occurs from decreased water surface slope, shear stress and velocity upstream of dams. However, high flows do facilitate some transport of suspended sediment over dams. Observations of abandoned dam sites and a dam breach revealed that much of the sediment stored above beaver dams is evacuated downstream quickly following a breach, but that a patchwork of preserved sediment may remain for several years following a breach and may be stored for longer periods on the floodplain. Persistence of sediment within the main channel on Odell Creek is limited by frequent breaching (<1 – 5 years), so a long-term rise in bed elevation from beaver related channel filling is not likely if current processes continue. However, if beaver remain in the system, sites along the stream will be in different stages of beaver occupancy, promoting maintenance of habitat heterogeneity and invigorating riparian zones through overbank flow along the stream corridor.

Degree Name

Earth and Planetary Sciences

Level of Degree

Masters

Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Gutzler, David

Second Committee Member

Weissmann, Gary

Project Sponsors

National Science Foundation; Geological Society of America; University of New Mexico Department of Earth and Planetary Sciences

Language

English

Keywords

fluvial geomorphology, beaver dams, sediment transport, channel incision, channel aggradation, fluvial fan, channel change, Greater Yellowstone Ecosystem, beaver

Document Type

Thesis

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