RECENT ADVANCES IN HEAT AS A TRACER OF STREAM EXCHANGES WITH SHALLOW GROUND WATER

Heat-tracing tools being developed with university, national lab, and USGS colleagues are summarized in the areas of novel instrumentation, tandem-tracer analysis, time-series analysis, inverse simulation modeling, and thermal analysis over expanded spatial scales. On the Russian River (CA) measurement advances in combined temperature/pressure transducers are providing the basis for heat tracing in a single probe. Along the Russian River, Santa Clara River (CA), and the Truckee River (NV) simultaneous analysis of the relative travel times and attenuation of heat versus other environmental tracers, such as chloride and specific conductance, may lead to improved understanding of the influence of heterogeneity on spatial and/or temporal variability in the rate of stream water exchanges with shallow ground water. On the Parajo River (CA) time-series analysis of streambed thermal records is leading to a method for robust, continuous measurements of streambed seepage, even with significant seasonal scour/deposit cycles. The value of using hypothetical simulations for potentially optimizing data-acquisition plans prior to equipment installation is discussed using examples from these field sites. New work on a tributary of the Snake River (WY), using a fiber optic based distributed temperature measurement system (DTS), may lead to spatially continuous temperature measurements longitudinally along entire stream reaches. Expansion efforts to three-dimensional, heat-tracing models, such as SUTRA and Tough2, are illuminating the nature of heat and water transport through surface clogging layers, unsaturated sediments, and hydraulically isolated layers beneath rivers, as well as during hyporheic exchanges. Potential for heat as a tracer based on remotely sensed stream temperatures is an emerging research area, with promising results reported by other researchers for forward-looking infrared (FLIR) imaging on the watershed scale.