LB 14-130 - Modification of the flow regime at the Kinzua Dam and impacts to nutrient and sediment fluxes in the upper Allegheny River.

Beginning in the late 1700s, rivers throughout the United States began undergoing hydrological modifications to facilitate multiple human uses, including economic development, flood control, irrigation, and power generation, resulting in a modified flow regime. Large impoundment dams, many built during the “big dam era” of the 1930s-60s, create an array of ecological, hydrological, and geomorphological impacts above and below the dam. In particular, dams disconnect the river continuum of sediment and nutrient transport. To address this disconnect, the United State Army Corps of Engineers (USACE) and Nature Conservancy have partnered to reintroduce natural flow regimes by adjusting dam operations to more closely follow historic seasonal flow trends in a suite of 44 US rivers included in the Sustainable Rivers Program (SRP). The Allegheny River, a headwater tributary to the Ohio River that spans New York and Pennsylvania, is a relatively new addition to the SRP where flow modifications have been in planning since 2013. On the Allegheny River, the Kinzua Dam stores peak flows for flood control below the dam and supplements low flows during summer and fall months to maintain navigable depths and water quality downstream. In March 2023, the first experimental flow modification on the Allegheny River took place with an experimental spring flood release of approximately 1.5B ft3 of water from the dam over a 27-hour period. In partnership with the USACE, students and faculty from the University of Pittsburgh’s Ecosystems: Land-Water-Atmosphere Interactions (GEOL 3853) course designed and implemented a sampling campaign to characterize the pulse release. In this late-breaking abstract, we explore the impact of this pulse release on the dynamics of water quality, geomorphology, and riparian ecology by coupling continuous sensing, grab sample chemistry, and isotopic composition. Here, we focus on findings related to fluxes of nutrients and sediments during the pulse, as well as indications of nutrient and sediment sources from upstream and downstream processes. This work advances our understanding of pulse release effects and will help inform future changes to dam operations for the purpose of river restoration.