TRACING THE ORIGIN OF FINE-GRAINED SEDIMENTS ENTERING A RESERVOIR USING RADIONUCLIDES

This project focused on impairment of drinking water reservoirs due to the overload of sediment delivered by rivers. Impairment may either be from fine-grained sediment impacting water quality and/or the delivery of sediment that decreases the reservoir's capacity to hold drinking water. Investigating where this sediment is coming from will help derive management solutions to minimize sediment delivery. In this study four cores were collected from various points along the main trunk of the Rockaway River to determine if there was spatial variation in source of sediments. The Rockaway River leads into the Boonton Reservoir in northern New Jersey, and both are located in the Highlands Region of New Jersey that supplies drinking water to over five million people. Each core is around ten to twenty centimeters long and was analyzed by one to two centimeter intervals in a gamma detector. The origin of sediment was determined by analyzing the radionuclide activity of Pb²¹⁰ and Cs¹³⁷. The activity in the first core of sediments show low levels of Pb²¹⁰ and minimal Cs¹³⁷, suggesting this sediment is coming from sources such as river channel erosion and other sources (such as hillslope failures) that contribute sediment from deeper depths than just surficial, overland flow. Three other cores were taken to examine the source of the sediments longitudinally along different parts of the river. Varying sources of sediment may cause impairment and so different mitigation efforts might be taken at different locations. Mitigation efforts such as river bank and hillslope stabilization may be needed to reduce the delivery of fine grained sediment to the river and reservoir.