Date of Award:

12-2021

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Watershed Sciences

Committee Chair(s)

Joseph Wheaton

Committee

Joseph Wheaton

Committee

Patrick Belmont

Committee

Nicolaas Bouwes

Abstract

For centuries river management and land use actions in North America have caused widespread stream degradation where water now flows downstream with artificially high efficiency. When present, beaver dams slow the flow of water and decrease the efficiency of water conveyance through the landscape. These effects are often to the benefit of the function of natural physical processes and ecology of the stream. The benefits provided by beaver dams have been well studied at small scales, but the methods that these studies rely on are often expensive and time consuming and consequently not feasible to deploy at larger spatial scales or in diverse physical settings. We propose a tractable framework to monitor riverine systems that is based on mapping inundation, or flooding patterns. We mapped inundation area and type (types = free flowing, ponded, and overflow) in beaver dam complexes in diverse physical settings in which beavers tend to build different types of dams. Our mapping of over 75 snapshots of inundation at 37 sites suggest that beaver dams change inundation patterns by creating more diverse surface inundation patterns and slowing down water so that more inundation can occur, even at low flows. On average, at 37 sites, undammed conditions inundate 6.8% (range of 2.7% to 17.4%) of their valley bottoms at low flows. In contrast, sites with beaver dams present inundate 23.3% (range of 9.5% to 47.5%) of the valley bottom at low flows. Undammed sites predominately exhibited free flowing ( > 99%) inundation, whereas dammed sites had a mix of all three inundation types. This research also reveals that low slope and the small size of streams most typically reported in beaver dam studies are unnecessarily restrictive. We report notable changes to inundation patterns in both steeper gradient ( > 6%) streams and in the floodplains of larger rivers where beaver do not typically dam the main channel. This research also proposes the use of inundation mapping as a proxy for other important physical processes that are difficult to explicitly measure.

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