https://hdl.handle.net/10388/17600

Ronnquist, Amanda Lee (2018) Persistence of beaver through the Alberta flood of 2013, Harvest - Theses & Dissertations, https://hdl.handle.net/10388/17600

INTRODUCTION: On June 19, 2013, heavy rain began to fall in the front ranges of the Canadian Rocky Mountains in Alberta, Canada. For three days the rain persisted, rapidly melting the alpine snow and creating flood conditions that resulted in the costliest natural disaster in Canadian History (Pomeroy et al., 2016). While this event was the largest Canadian Rocky flood to occur in the past 60 years, its relatively short return period of approximately 40 years ensures similar events will occur in the future (Pomeroy et al., 2016). The short return period associated with a storm of this magnitude has prompted concerns and discussion of potential strategies to assist with future flood prediction and mitigation. As a response to the flood, three categories of management were proposed: prediction, avoidance, and active mitigation (Pomeroy et al., 2016). Active mitigation on the landscape would involve the implementation of flood-control structures such as dams, and detention ponds, as well as dikes and channel modifications. Interestingly this landscape already contains many dams, ponds, and modified channels. However, they are not man-made structures but are build by the North-American Beaver (Castor canadensis). This prompts questions regarding how beaver modifications on the landscape affect the hydrology of the system during large flood events. The population of beaver in North America (Castor canadensis) is currently rebounding due to conservation efforts and an increasing awareness to the beavers role in watershed ecosystems (Pollock et al., 2017). Beaver dams are important structural elements of channels and can have significant affects on the fluvial geomorphology and hydrology of watersheds (Gurnell, 1998). Beaver dams are known to affect the hydrology of stream systems through increases in surface ponding and wetland habitat area (Hood and Bayley, 2008; Johnston and Naiman, 1990); as well as increases in groundwater storage (Karran et al., 2018; Westbrook et al., 2006). Furthermore, past studies comparing streams with and without beaver modifications have shown that beaver dams decrease the overall peak discharge of floods, attenuate flood peaks for small flood events (up to and slightly above bankfull), and dissipate energy downstream (Gurnell, 1998). (Law et al. 2016). There has been increasing interest in utilizing green infrastructure to assist in flood mitigation including increasing the amount of beaver dams found in a system (Palmer et al., 2015; Pollock et al., 2017). However, the resilience of an entire landscape of beaver modifications in response GEOG 490 | 2018 Page | 4 to very large acute flooding events is inadequate. A natural assumption is that high precipitation, rapid snowmelt, and the collapse of upstream dams will result in severe dam failure downstream (Gurnell, 1998). This could result in a potential domino-effect, releasing water-sediment surges and resulting in the severe entrenchment of streams (Marston, 1994). Further investigation is required to determine if these structures can persist on the landscape through a flood of this magnitude before exploration regarding their use as a reliable flood mitigation strategy can commence. The occurrence of a flood of this magnitude provides an invaluable opportunity to observe how beaver dams respond to large floods on a landscape scale. The objectives of this research are to (1) determine the level of persistence of beaver sites through the flood of 2013 and (2) identify and analyse factors that may have allowed the persistence of some sites over others. This knowledge will provide insight into the role beaver dams play during large flood events and will potentially lead to assisting regulators, land managers, and other parties interested in the viability of beaver as a tool for flood mitigation

https://hdl.handle.net/10388/17600