Date of Award:

5-2017

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Watershed Sciences

Committee Chair(s)

Joseph Wheaton

Committee

Joseph Wheaton

Committee

Brett Roper

Committee

Philip Bailey

Abstract

Dams built by North American Beaver create natural water storage and slow water as it moves through streams. In portions of streams with beaver dams, these effects have been observed to decrease the peak magnitude of floods and increase base flow during annual summer droughts. In the western United States changes to streamflow patterns have been observed in recent decades with large spring floods coming earlier in the year, causing annual summer droughts to start earlier and last longer. These changes are linked to decreasing snowpack which acts as the most significant natural water storage reservoir by holding onto precipitation for many weeks to months and slowly releasing the water as it melts.

Given that snowpack is decreasing with warming temperatures, beaver dams provide a conceptually similar function to snowpack by increasing the residence time of precipitation as it travels through a drainage. Given that beaver dams can occupy large portions of the drainage network, it is logical to look to what degree beaver dams could compete with losses from snowpack. There are two ways in which beaver dams could buffer losses. One is through providing additional temporary water storage in both ponds and increases in groundwater storage. The second is through altering the timing and delivery of water downstream by increasing the time it takes to move downstream. I consider the first mechanism in this thesis, though to consider the second mechanism one needs an understanding of the first.

I test the idea that the additional water storage from increasing the number of beaver dams in a watershed could compensate for decreases in snowpack by simulating the amount of water beaver dams could store under different scenarios of both snowpack loss and the number of beaver dams on the landscape. To do this I first collect observations of 500 beaver dams to quantify the distribution of beaver dam sizes, then use this distribution to develop a model that predicts water storage using dam location and dam size. Results from the model of surface water storage are then input to an existing groundwater model to estimate increases in groundwater storage. Overall, our estimates suggest that beaver dams could store 6.65 million m3 (6,000 acre-feet) of water in the Bear River basin, a small fraction of water lost from snowpack (1043.83 million m3, 845,000 acre feet), where watersheds with the highest beaver dam water storage capacity account for approximately 3% of estimated snow water equivalent loss. However, in many watersheds beaver dam storage may account for close to 100% of snow water equivalent loss in valley-bottoms. Though storage from beaver dams may be limited, it could have significant impacts where human-made reservoirs are not available to regulate water resources. Furthermore, these small amounts of water storage, while ecologically significant, may not result in measurable changes to water availability for downstream water users which could present legal implications for beaver-based restoration strategies.

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