The Viability of Hyporheic Zone Restoration for Improving Groundwater and Surface Water Exchange in an Urban Watershed
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Restoring the Unseen River: The Viability of Hyporheic Zone Restoration for Improving Groundwater and Surface Water Exchange in an Urban Watershed by Chapin Pier A Thesis Submitted in partial fulfillment of the requirements for the degree Master of Environmental Studies The Evergreen State College June 2015 © 2015 by Chapin Pier. All rights reserved. This Thesis for the Master of Environmental Studies Degree by Chapin Pier has been approved for The Evergreen State College by ________________________ Erin Martin, Ph.D. Member of the Faculty ________________________ Date i ABSTRACT Restoring the Unseen River: The Viability of Hyporheic Zone Restoration for Improving Groundwater and Surface Water Exchange in an Urban Watershed Chapin Pier Stream restoration is a growing field aimed at mitigating stream degradation caused by human development and urban expansion. Traditionally, stream restoration has focused on surface water and riparian aspects of stream systems. Rarely have restoration projects considered the hyporheic zone (HZ), which exists below the streambed where surface water and groundwater interact. The hyporheic zone provides many benefits, which include, nutrient and energy cycling, temperature regulation, and habitat and refuge benefits. While there is increasing awareness of the hyporheic zone, stream restoration projects rarely incorporate hyporheic zone focused restoration methods. In the fall of 2014, two restoration projects were completed in the highly urbanized Thornton Creek watershed in Seattle, Washington. The restoration projects were innovative because they incorporated an engineered reconstruction of the hyporheic zone, which was intended to improve HZ exchange. The primary objective of this study is to examine the impacts of restoration on hyporheic zone exchange at the restored sites. During the winter of 2015, intensive streambed temperature surveys were conducted at the restored sites and nearby control (unrestored) sites to track the movement of water through the HZ. The surveys were intended to locate zones of upwelling and downwelling by tracking the movement of heat between the surface water and groundwater zones. Hyporheic zone exchange was anticipated to be greater at the restored sites than the control sites. Furthermore, exchange was expected to be greatest at locations immediately adjacent to in-stream structures, which were installed during restoration. The results indicated that hyporheic zone exchange was greatest at the control sites when compared to the respective restored sites. However, the results of the surveys were inconclusive due to multiple discrepancies that existed between the sites that couldn’t be accounted for in this study. For instance, differences in water residence time may have led to differences in heat transfer at the distinct sites, which may explain the unexpected results of the surveys. Less surprising, the surveys did find that HZ exchange was greatest adjacent to in-stream structures. This study was intended to be an initial investigation of hyporheic zone exchange post- restoration and does not provide definitive conclusions. However, the results of this study will be correlated with future surveys at the restored sites to better understand both the effectiveness of restoration and also how HZ exchange changes over time. Overall, this study highlights the need for future research to better understand the potential benefits and limitations of stream restoration for improving hyporheic zone function. ii Table of Contents Abstract .............................................................................................................................. ii Table of Contents ............................................................................................................. iii List of Figures .....................................................................................................................v List of Tables ................................................................................................................... vii Acknowledgements ........................................................................................................ viii Chapter 1: Introduction ....................................................................................................1 Chapter 2: Literature Review ...........................................................................................3 Literature Overview .........................................................................................................3 Urban Streams ..................................................................................................................3 Urban Stream Restoration ................................................................................................6 Hyporheic Zone Function and Importance .......................................................................7 Historical Research ........................................................................................................11 Hyporheic Zone Research ..............................................................................................12 Hyporheic Zone Restoration ..........................................................................................14 Thornton Creek Background ..........................................................................................18 Thornton Creek Restoration Projects .............................................................................20 Conclusion ......................................................................................................................23 Chapter 3: Methods and Analysis ..................................................................................24 Field Study Overview .....................................................................................................24 Survey Procedures ..........................................................................................................25 GPS Surveys ...................................................................................................................28 Spatial and Statistical Analysis ......................................................................................28 Chapter 4: Results............................................................................................................31 Knickerbocker ................................................................................................................31 Knickerbocker Control ...............................................................................................32 Knickerbocker Treatment (Upstream) ........................................................................36 Knickerbocker Treatment (Downstream) ...................................................................38 South Fork Confluence ...................................................................................................40 South Fork Confluence Control..................................................................................42 iii South Fork Confluence Treatment (Upstream) ..........................................................45 South Fork Confluence Treatment (Downstream) .....................................................47 Influence of Habitat Type on Temperature Anomalies ..................................................48 Knickerbocker Sites ....................................................................................................48 South Fork Confluence Sites ......................................................................................50 Influence of Substrate Type on Temperature Anomalies ...............................................51 Chapter 5: Discussion ......................................................................................................52 Summary of Findings .....................................................................................................52 Knickerbocker ................................................................................................................54 South Fork Confluence ..................................................................................................57 Warm Winter Temperatures ...........................................................................................58 Substrate Clogging .........................................................................................................59 Post-restoration Equilibrium ..........................................................................................60 Chapter 6: Conclusion and Implications for Future Research ...................................61 References .........................................................................................................................63 iv List of Figures Figure 1 ...............................................................................................................................5 Pre-project photograph of the South Fork of Thornton Creek flowing through a culvert underneath 35th Ave. N.E. in Seattle, WA (City of Seattle). Figure 2 ...............................................................................................................................8 Flow of water through the hyporheic zone at different scales (Boulton et al, 2010). Figure 3 .............................................................................................................................19 Location and boundary of the Thornton