Seepage investigations and discharge measurements at Oregon Caves National Monument and Preserve, 2021-2024

This data release pertains to a seepage investigation conducted in order to compliment a dye tracing study at Oregon Caves National Monument in Josephine County, Oregon. The seepage dataset includes geospatial files of discharge measurement points and zero-flow observations along with vector lines delineating losing and gaining stream reaches.

Hydrologic systems in karst environments have a high degree of interconnectivity between surface water and groundwater systems. Because of this interconnectivity, activities which occur on the surface in karst environments have a direct impact on the water quality and quantity of karst groundwater. Losing streams are where stream flow sinks or loses into the subsurface, either along a reach or potentially at a discrete point. This flow may reappear further downstream within the same drainage or may follow karst pathways (such as fractures and conduits) to springs, caves, or other drainages. Thus, in karst areas with losing streams, awareness of the locations where stream flow is lost or gained is necessary to properly understand the karst hydrologic system and the influences on water quality. In addition to quantifying stream flow losses and gains, knowing the pathway(s) that the sinking water follows is necessary as karst flow paths are unpredictable. Dye injections of fluorescent tracer dyes can be conducted to trace the sinking water to resurgences that can be monitored.

Within Oregon Caves National Monument and Preserve (ORCA) are areas underlain by marble, a metamorphic carbonate rock susceptible to karst development. In areas underlain by marble, streams may sink or lose flow to the subsurface, ultimately draining to caves and springs. In 2021 and 2024, dye tracing was conducted at ORCA to map karst groundwater pathways and delineate recharge areas for major springs and caves. In August 2021 a second round of dye injections were planned but required additional information in order to select appropriate dye injection sites. This information related to whether selected streams were losing to the subsurface, thus contributing to karst groundwater systems, or if the streams were gaining flow or merely were stable (no increase or decrease). From August 24 through September 2, 2021, streams were measured for discharge so that reaches above, within, and below marble outcrops were investigated to determine whether streams were losing substantial flow to the karst groundwater system. Seepage runs were conducted along reaches of four streams, including Lake Creek, Panther Creek, Cave Creek, and No Name Creek. These seepage investigations resulted in 15 discharge measurements and 2 zero-flow observations along the selected streams. As part of this data release, an additional five discharge measurements were made throughout the larger dye tracing study at springs, streams, and cave streams.