PNNL

Abstract

Mapping and quantifying hydrologic exchange flows (HEFs) is critical to addressing diverse hydrologic and engineering problems including environmental monitoring and remediation design at contaminated sites; however, these objectives are challenging in highly dynamic systems, such as those with dam-regulated rivers, where HEFs vary rapidly and may reverse direction. Conventional, direct approaches rely heavily on point measurements (e.g., seepage meters), which are labor-intensive and difficult to automate. Characterization by automated methods and (or) remote sensing methods has potential to allow continuous monitoring with limited field effort at lower cost relative to direct approaches and without sacrificing resolution. In this paper, we present a preliminary assessment of a multi-scale temperature-based approach for autonomous monitoring of HEFs along the Hanford Reach of the Columbia River, in eastern WA, USA. Five types of thermal data were acquired and assessed. First, in situ vertical temperature profiles (VTPs) were installed into the streambed at study sites where upwelling from groundwater was previously observed or suspected; these data were analyzed to estimate flux for comparison to the three other data types. To resolve rapid changes and reversals in HEF, we use a recently published data assimilation algorithm; this algorithm is well suited to automated real-time estimation, which is the long-term objective of this work. Second, a handheld thermal infrared (TIR) camera was used in roving surveys to identify areas of focused exchange, both through the stream bank and the bed. Third, a TIR camera was stationed at one of the VTP sites and programmed to take images from a downward planar view at 1-hour time intervals. The two TIR datasets (i.e., roving spatial and fixed time-series) provide a basis to assess the potential for drone-based TIR imaging to map and monitor HEFs in the future. Fourth, a thermistor was installed at the sediment/water interface to measure bed temperature; this dataset provides a basis to assess fiber-optic distributed temperature sensing at sites with estimated flux from the VTP. Fifth, thermal imagery from the ECOSTRESS satellite mission was acquired to assess the potential of low-cost/high-coverage spaceborne monitoring of discharge. Based on our preliminary assessment, a combination of thermal data streams has potential for long-term, automated monitoring to understand the spatial and temporal distributions of HEFs and quantify water flux at discrete locations. VTP, TIR, and bed temperature measurements provide complementary information with respect to spatial coverage, temporal sampling, and resolution, thereby enabling multi-scale characterization in the future. The spaceborne imagery, however, proved inadequate because of data gaps due to the low number of cloud-free images and insufficient spatial resolution.