This project is a quantitative physics-based study of the heat budget in the hyporheic zone of a large river. It is relevant to current research in the interactions between stream temperature and hyporheic water flux. Understanding heat transfer in hyporheic zones has important implications for water quality and its regulation in the western US, and may be a new tool for researchers, regulators, and water treatment professionals. Preliminary results indicate that warm river water undergoes hyporheic cooling during its transit beneath gravel bars. River-restoration and pollution-credit-trading schemes are being designed around hyporheic cooling strategies, and this makes a full understanding of this phenomenon an imperative. Initial hypotheses include: (1) warm, daytime water is not actually cooled in the hyporheic zone but does push out cool, nighttime water during the day, (2) warm, daytime water is significantly cooled by a) heat flow by conduction to and mixing with deeper groundwater with longer flow paths, b) heat flow by latent and sensible heat fluxes to the vadose zone, and/or c) temporary heat storage in gravels and dead zones in the hyporheic zone. Preliminary tests of these hypotheses will be accomplished through field instrumentation and modeling of water and heat fluxes beneath a gravel bar on a large, gravel-bed river, the Willamette River, Oregon. The research site represents a recently deposited gravel bar of the type found to provide significant apparent cooling. Field data from, site surveying and mapping, shallow wells, seismic profiles, and tracer tests, will characterize and facilitate modeling of the substrate and associated fluxes. This characterization and modeling will constrain the scope and methods for a follow-up study of (1) the adequacy of the platform layout of wells to measure laterally advective heat fluxes, (2) the need for additional wells to measure deeper heat fluxes and storage, (3) the need for three-dimensional seismic data acquisition and/or full tomographic analysis and waveform modeling, to determine boundary conditions.
