TRACING THE RIVER STYX: HYDROLOGIC INSIGHTS AND MANAGEMENT OF THE NATION’S ONLY SUBTERRANEAN WILD AND SCENIC RIVER

Nestled beneath the rugged karstic terrain of Oregon Caves National Monument and Preserve lies the River Styx, the only subterranean Wild and Scenic River in the National Park Service. This feature attracts thousands of visitors annually, making it a top priority for park management, but both the distinctive nature of the cave stream and complex geology of the park complicate stewardship efforts. The marble unit that hosts Oregon Caves is part of a complex mélange of accreted, metamorphosed terranes that compose the Applegate Group. While understanding interactions between the karst systems of these terranes is critical for managing the River Styx, subsurface interactions within and among these systems remain poorly constrained, hindering the development of effective management strategies.

Non-toxic fluorescent dye injections were conducted by the US Geological Survey, working with the National Park Service and Student Conservation Association to delineate recharge areas and understand connection among kart systems within the Park. Dye traces from these injections identified hydrologic connections between River Styx and previously unknown resurgences below the cave mouth, as well as establishing hydrologic connections to several major sinking streams. However, despite the proximity of Oregon Caves to the next longest cave system in the park, Cave Next Door, the dye traces revealed that these systems drain distinct recharge areas, highlighting the complexities of hydrogeology in these types of geologic settings. Ongoing work will refine our understanding of variable karst groundwater velocities and storage within karst aquifers discovered during dye tracing to better inform management strategies.