IDENTIFICATION OF FOCUSED GROUNDWATER DISCHARGE IN A WETLAND STREAM USING A DISTRIBUTED TEMPERATURE SENSOR

Zones of focused groundwater discharge have been identified in a wetland stream through fine-scale spatial (1 meter) and temporal (60 second) measurements using a fiber-optic-based distributed temperature sensor. A one-kilometer long fiber-optic cable was placed just below the sediment/water interface in a peat-dominated wetland stream in Northern Wisconsin. The difference in temperature between groundwater and surface water was used to identify zones of focused groundwater discharge along the streambed. Results show a deviation from the traditional concept of diffuse flow commonly used to describe groundwater/surface water interactions within streams. The location of focused zones of groundwater discharge were identified and shown to be stable through time. Seepage-meter measurements conducted in two of the focused discharge zones showed two orders of magnitude more discharge as compared to non-focused discharge zones. The focused zones of high groundwater discharge are likely a result of soil pipes within the peat-dominated wetland. Distributed temperature sensor measurements appear to have great potential to locate zones of groundwater discharge, especially when supplemented with data collected using seepage meters, stream gaging, thermocouple probes and forward looking infrared (FLIR) images.