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Using Temperature Measurements to Map and Quantify Flow across the Sediment/Water Interface
Citation:
Day-Lewis, F., M. Briggs, J. Lane Jr., AND D Werkema. Using Temperature Measurements to Map and Quantify Flow across the Sediment/Water Interface. 2019 Sediments Conference, New Orleans, LA, February 11 - 14, 2019.
Impact/Purpose:
Heat tracing is a cost-effective method to map and quantify fluid flux across the sediment/water interface (SWI). Although technological advances have greatly improved our ability to measure temperature, ‘Big Data’ datasets pose challenges to standard approaches for analysis and interpretation. New tools, such as DTSGUI and 1DTempPro, facilitate rapid and cost-effective analysis, enabling high-resolution insights to support diverse scientific and engineering needs.
Description:
Background/Objectives. Flow across the sediment/water interface (SWI) has important implications for diverse hydrologic and engineering problems including remediation of groundwater (GW) and sediments in streams, lakes and estuaries; management of aquatic habitats; and water-resource management. GW/SW interaction generates redox and biogeochemical gradients within the upper 10’s of cm below the SWI, resulting in a dynamic environment where contaminants, nutrients, and greenhouse gases (e.g., N2O) can be transformed, sequestered, released, or even produced. Quantifying fluid flux across the SWI is necessary to estimate chemical loading and develop conceptual and predictive models for engineering design. Temperature-based inference of fluid flux (i.e., heat tracing) is well established, cost effective, and increasingly common; these approaches capitalize on GW/SW temperature contrasts to qualitatively map reaches of enhanced exchange or quantitatively estimate flux using analytical or numerical models. Increasing application of these approaches is driven by more widespread adoption of fiber-optic distributed temperature sensing (FO-DTS) and infrared cameras, and by newly available tools for processing, visualizing, and modeling temperature data. Here, we review and present case studies demonstrating the (1) application of FO-DTS for qualitative mapping of exchange zones, (2) modeling of temperature profiles to quantify vertical fluxes, and (3) new U.S. Geological Survey software for heat tracing. Approach/Activities. FO-DTS produces large, information-rich temperature datasets with precision of ~0.1ºC, at approximately 0.25-1.0 m spatial resolution, at ~1-min intervals, along one or more cables each of which can be up to several km long. Interpretation of these datasets can yield high-resolution (in space and time) insights into patterns of GW/SW exchange, but parsing such large and complex datasets is challenging. The FO-DTS data need to be georeferenced, and the data interpolated in space between known locations, often hindering efficient spatial analysis during field efforts. Here, we demonstrate DTSGUI, a new python-based open-source public-domain code. DSTGUI reads and displays FODTS data using the Google Maps API, georeferencing the data based on GPS measurements at locations along the FODTS cables. The code offers functionality to edit datasets, focus on times/intervals of interest, and map summary statistics (min/max, mean, standard deviation) to facilitate interpretation. DTSGUI allows for rapid insight into GW/SW exchange during field efforts. For over 50 years, vertical temperature profiles have been used to quantify fluxes across the SWI. The approach uses measurements of temperature at different depths, collected over time, and calibration of either analytical or numerical models to infer flux and, in some cases, hydraulic properties. We demonstrate 1DTempPro, a C#-based open-source public-domain code which allows the user to calibrate a heat-transport model to vertical temperature profiles.