KARST INVESTIGATIONS AT THE WALKER BRANCH WATERSHED, OAK RIDGE, TENNESSEE

The Walker Branch watershed at Oak Ridge National Laboratory (ORNL) is perhaps the best studied small watershed in Tennessee. ORNL maintains a website dedicated to the research conducted at Walker Branch, and a book published in 1989 summarized conclusions from numerous studies of biological, hydrological and geochemical processes at Walker Branch. Although water budget computations at Walker branch are complicated by the presence of sinking streams and springs, karst processes have historically not been a focus of research at the site. Nevertheless, the abundance of local rainfall records, streamflow measurements, water chemistry data, and published studies that include an evaluation of groundwater contributions to stream discharge make the site ideal for determining recharge rates in similar geologic settings in East Tennessee.

Published studies at Walker Branch indicate significantly higher recharge rates to the Knox aquifer than had been suggested by workers developing a site conceptual model for the hydrology of the Oak Ridge Reservation and by published United States Geological Survey analyses of streamflow data in the Valley and Ridge physiographic region of Tennessee. A tracing investigation using fluorescent dyes was conducted to better determine potential contributions of water imported from or exported to adjacent watersheds. Tracing confirmed that water lost from the east fork of Walker Branch above the gaging point discharged at three locations. Dye introduced into a losing reach near the headwaters of the stream discharged to the west fork of Walker Branch and at a spring downstream of the gaging stations. Dye introduced in a swallet downstream discharged at the same spring and at an overflow spring just above the east fork gaging station. There was no evidence for export of water into adjacent watersheds.