Author(s): Italyivo Martone, Carlo Gualtieri, Ted Endreny

Linked Author(s): Carlo Gualtieri, Ted Endreny

Keywords: Hyporheic exchange; Confluence hydrodynamic; Vertical hydraulic gradient; Heat tracing; Hydraulic conductivity;

Abstract: Confluences are ubiquitous components of all riverine systems, and are characterized by converging flow streamlines, mixing of flows and a highly complex three-dimensional flow structure located in the so-called Confluence Hydrodynamic Zone (CHZ). The CHZ generally includes a zone of flow stagnation near the upstream junction corner; an area of flow deflection as the tributary enters confluence; shear layer and/or mixing interface between the two converging flows; a possible separation zone at the downstream junction corner(s); flow acceleration within the downstream channel; and flow recovery at the downstream end of the CHZ. The aim of this study was to assess how the above features affect the ecologically important hyporheic fluxes between surface and subsurface waters, and hence guide the management and restoration of the whole river environment. Field investigations were carried out in Onondaga County of central New York, U.S.A. during the 2018 summer to fall seasons. The study case was a 2-meter-wide confluence between Baltimore Brook and Cold Brook forming a 45 degrees junction angle. Field campaigns yielded surveys of channel bathymetry, discharge rates, hydraulic conductivity, and substrate roughness, while probes measured hyporheic zone vertical hydraulic gradient and temperature profile data. Initial findings show spatial variation in the direction of vertical fluxes directions (upwelling and downwelling) during the sampling time period. Confluence morphology and water table gradients beyond the channel domain are affecting magnitude and pattern of hyporheic exchange. These data combined with models could help to advance the understanding of the key hydrological, hydraulic, and ecological issues associated with rivers confluence.

DOI: https://doi.org/10.3850/38WC092019-1227

Year: 2019