THESIS RIVERS AND BEAVER-RELATED RESTORATION IN COLORADO Submitted by Julianne Scamardo Department of Geosciences In partial fulfillment of the requirements For the Degree of Master of Science Colorado State University Fort Collins, Colorado Fall 2019 Master’s Committee: Advisor: Ellen Wohl Tim Covino Ryan Morrison Copyright by Julianne Eileen Scamardo 2019 All Rights Reserved ABSTRACT RIVERS AND BEAVER-RELATED RESTORATION IN COLORADO Interest in beaver-related restoration, such as reintroduction and dam analogs, for repairing incised and degraded streams is apparent across the American West. North American beaver (Castor canadensis) were historically abundant across their ecological range, and headwater streams across the U.S. likely held many beaver dams in the channel and on the floodplains. Beaver dams can effectively trap sediment, water, and solutes, and a thriving beaver meadow can have implications for biodiversity and carbon storage. After historical declines in populations throughout the 19th and 20th century, enthusiasm for reintroduction and dam analogs has grown for naturally restoring degraded streams that once housed beaver. To guide enthusiasm in the State of Colorado, understanding (i) where reintroductions are viable and (ii) how beaver dam analogs change stream morphology and hydrology is critical. This study tackles those two objectives by modeling potential dam densities in 63 watersheds across Colorado as well as monitoring beaver dam analog restoration projects in two watersheds in the Colorado Front Range. While density models may not be accurate at small scales, regional patterns in dam density across Colorado suggest that many streams can still support beaver populations despite larger decreases from historic dam densities. Reintroductions could spur vegetation growth and create side channels through overbank flow, which would increase the capacity of a given stream to support beavers. On streams where densities are low or have been reduced to no beaver capacity, beaver dam analogs could be installed to aggrade channels and create ponds. Unlike natural beaver dams, the beaver dam analogs monitored here did not create ii a groundwater response within the first year of restoration, which could be a limitation to restoration projects hoping to increase riparian vegetation. However, this study only covers the first year post-restoration and long-term restoration outcomes could differ from the short-term. In the future, smaller scale watershed modeling and site visits to watersheds or streams with high modeled dam densities are necessary to determine precise stream reaches that are prime for reintroductions. Additionally, post-restoration studies that extend over a longer time frame and include more watersheds are needed to fully understand the magnitude of change post-beaver- related restoration. iii ACKNOWLEDGEMENTS This research and the past two years at CSU were supported and made possible by so many. First, I would like to thank my advisor, Ellen Wohl, whose scientific curiosity and enthusiasm helped build this project to include the myriad ideas, people, and watersheds that it did. Her patience, guidance, and diligence over the past two years has helped me become a better researcher and communicator. My committee – Ryan Morrison and Tim Covino – have also helped shape the ideas of this project as well as provided assistance and advice in the execution of the details. I would like to thank the many people who came out in the field – Darrick Roanhaus, Ethan Ader, Alex Brooks, Johanna Eidmann, and more – to help with some of the more arduous aspects of my field work. Thank you to the fluvial lab – especially Ethan Ader and Sarah Hinshaw – for countless laughs, cries, and adventures. Allie Rhea and Johanna Eidmann are included in that acknowledgement for all the encouragement, wisdom, and fun they have shared with me over the last two years. I would also like to thank my partner, John Kemper, for his unbelievable patience, lively scientific debates, and unwavering confidence in me. Beyond the flamily, I would like to thank my family, who have always supported my love of the outdoors and my academic pursuits, wherever they have taken me. Finally, this project was made possible due to funding from Boulder County Parks and Open Spaces, City of Boulder Open Space and Mountain Parks, Geological Society of America, Colorado Scientific Society, and Colorado Mountain Club Foundation as well as collaboration with the Wildland Restoration Volunteers and Cheley Ranch. iv TABLE OF CONTENTS Abstract ........................................................................................................................................... ii Acknowledgements ........................................................................................................................ iv Chapter 1 – Modeling current and historic beaver dam density in Colorado, USA ........................1 1. Overview ..........................................................................................................................1 2. Introduction and Previous Studies ...................................................................................2 3. Methods............................................................................................................................7 3.1 Description of Study Area .................................................................................7 3.2 Model Inputs and Parameters.............................................................................8 3.3 Preprocessing ...................................................................................................12 3.4 Case Studies .....................................................................................................13 3.5 Dam Statistics ..................................................................................................18 4. Results ............................................................................................................................19 4.1 Current and Historic Dam Densities ................................................................19 4.2 Temporal Changes to Dam Density .................................................................24 4.3 Case Study Comparisons .................................................................................27 5. Discussion ......................................................................................................................30 5.1 Spatial Differences in BRAT ...........................................................................30 5.2 Temporal Differences in BRAT .......................................................................35 5.3 Case Studies .....................................................................................................40 6. Conclusions ....................................................................................................................46 References (Chapter 1) ..................................................................................................................48 Chapter 2 – The geomorphic effect of beaver dam analogs in the Colorado Front Range............53 1. Overview ........................................................................................................................53 2. Introduction and Previous Studies .................................................................................54 3. Objectives and Hypotheses ............................................................................................58 4. Site Description ..............................................................................................................61 5. Methods..........................................................................................................................65 5.1 Reach Selection ................................................................................................65 5.2 Surface Hydrology ...........................................................................................67 5.3 Shallow Groundwater Hydrology ....................................................................68 5.4 Channel Surveys ..............................................................................................71 5.5 Residual Pool Sediment Surveys .....................................................................71 5.6 Sediment Cores ................................................................................................74 6. Results ............................................................................................................................74 6.1 Surface Hydrology ...........................................................................................74 6.2 Shallow Groundwater Hydrology ....................................................................76 6.3 Residual Pool Surveys .....................................................................................82 6.4 Grain Size Analysis..........................................................................................88 7. Discussion ......................................................................................................................92 7.1 Determining Palpable Sediment Relationships ................................................92 7.2 Lack of Groundwater Response .......................................................................96 7.3 Design Influences BDA Response ...................................................................98