Influence of Restoration on Shallow Groundwater in Urban Forest Streams
Sandra Clinton, PhD
University of North Carolina at Charlotte
Geography and Earth Sciences
Charlotte, NC
Authors List: Petitt, D.N., Vinson, D.S., Clinton, S.M., & McMillan, S.
Urban headwater streams are good candidates for restoration where restoration alters environmental parameters and resulting water quality. The Reedy Creek Restoration Project, completed in 2019, reconstructed 7 urban streams in the 6km2 Reedy Creek watershed in the headwaters of the Pee Dee River watershed. Restoration followed the natural channel design approach with increased sinuosity and riffle-step-pool sequences. Here, impaired stream channels were recreated on nearby existing floodplains, raising the streambeds 1.5-3.5 meters across the watershed. Streams were reconnected to surrounding floodplains effectively increasing groundwater-surface water interactions. Moreover, raising the streambeds and lowering the gradient has the potential to increase groundwater storage. To monitor changes in groundwater, riparian groundwater levels (WLs) have been measured continuously since 2013 in 5 wells, and hillslope WLs have been measured since 2016 in 5 additional wells. Objectives of this study are to quantify: (1) interannual variability in WLs, (2) seasonal variations in WLs, and (3) how WLs have changed from pre (Pre-R) to post (Post-R) restoration.
Pre-R WLs fluctuated on average 85 cm interannually. Post-R WLs fluctuated on average 60 cm interannually. Water levels fluctuated seasonally on the order of 100 cm (Pre-R) and 90 cm (Post-R) during the fall/winter and spring/summer periods. After restoration, average WLs increased from Pre-R WLs of 340 cm to Post-R WLs of 210 cm below the land surface as a result of channel relocation and the new channel being much shallower than the Pre-R deeply incised channel. The riparian WLs tended to rise first after restoration, with one site’s WLs rising 102 cm in 8 weeks, followed by a rise in the corresponding hillslope WLs 2 months later; this may also be due to channel relocation. Overall, the Post-R watershed has increased groundwater storage leading to a gentler hydraulic gradient from the upland to channel and an increased potential for flooding. As the Post-R period continues, we are examining weekly baseflow stream and seasonal groundwater chemistry to determine the effect, if any, on water quality contributed by the newly saturated soil and saprolite since channel restoration.
About Sandra Clinton, PhD
Sandra Clinton is a Research Assistant Professor in the Department of Geography and Earth Sciences at the University of North Carolina Charlotte. Sandra's research focuses on how humans impact the structure and function of freshwater ecosystems. Her most recent research focuses on quantifying the impact of restoration practices on urban stream hydrology and ecology and the services and disservices provided by urban stormwater and beaver ponds.