QUANTIFYING SEDIMENT FLUXES INTO ENKA LAKE, A SOUTHERN APPALACHIAN COMMUNITY RESERVOIR

Throughout his career, Ken Bradbury designed and executed applied projects with an overarching public benefit, while also training students and pursuing fundamental questions and intellectual curiosities. Similarly, the project described here is the result of contributions from numerous research students and citizen scientists to investigate sediment fluxes into Enka Lake, a 62-acre reservoir in the Southern Appalachians of Western North Carolina (USA). Lake level is controlled by a dam built in 1933 to provide a water supply for a nearby industrial facility. In 2001, the lake and approximately 1000 acres were sold and developed into a residential community. The lake is now used primarily for recreation, with a beach, clubhouse, boathouse, and 2.2-mile walking/biking path around the lake.

During baseflow conditions, tributaries leading into Enka Lake are very clear (low turbidity/high transparency), but sediment-laden stormflow is associated with turbid water, higher nutrients, E. coli, and sediment buildup in the lake. To protect the recreational and aesthetic value of the lake to the community and its residents, a dredging program was carried out in 2016, and a sediment management study was commissioned in 2017. From 2018-2020, neighborhood residents and UNC Asheville student researchers collected nearly 500 water samples throughout the watershed. Sample bottles were distributed to volunteer samplers ahead of rainfall events; the sampling team communicated via group text ahead of predicted rainfall and in real time during “pop-up” thunderstorms to organize who could collect samples during and after the storm. All samples were analyzed for turbidity, and a subset were also analyzed for total suspended solids. We measured streamflow feeding into and draining out from Enka Lake, and used the sediment and streamflow data to construct sediment rating curves and estimate total sediment loads into the lake. We tested a sediment model with high-frequency sampling during and after three different storms, with the model largely matching total sediment fluxes but underestimating peak fluxes. Our estimate of total annual sediment load from the two largest tributaries suggests that the 2016 dredging project may have removed only about two years’ worth of sediment.