LSPIV Measurements of Two‐Dimensional Flow Structure in Streams Using Small Unmanned Aerial Systems: 2. Hydrodynamic Mapping at River Confluences. Issue 10 (19th October 2018)

• Record Type: Journal Article
• Authors: Lewis, Quinn W.; Rhoads, Bruce L.
• Is Part Of: Water resources research. Volume 54:Issue 10(2018)
• Page Start: 7981
• Page End: 7999
• Publication Date: 2018-10-19
• Subjects: LSPIV -- sUAS -- river confluence -- hydrodynamics; Hydrology -- Periodicals; 333.91
• DOI: 10.1029/2018WR022551
• Languages: English
• ISSNs: 0043-1397

Abstract

Abstract: Although past field work at stream confluences has relied on velocity information at specific cross sections to examine flow structure, detailed characterizations of spatial and temporal variations in the hydrodynamics of confluences are lacking. This study uses large‐scale particle image velocimetry (LSPIV) obtained from small unmanned aerial systems (sUAS), a method evaluated in a companion paper, to map surficial patterns of mean flow and turbulent structures at two small stream confluences in unprecedented levels of detail. LSPIV reveals two‐dimensional flow patterns within different hydrodynamic zones in each confluence as well as similarities and differences in hydrodynamic conditions between the confluences. As expected based on extant conceptual models of confluence hydrodynamics, the spatial arrangement of characteristic hydrodynamic zones varies with confluence planform geometry and with changes in incoming flow conditions. However, local morphological features, such as bars and irregularities in channel banks, also exert a strong influence on the spatial structure of flow and in some cases influence confluence hydrodynamics to an extent comparable to changes in incoming flow conditions. The usefulness of sUAS‐based LSPIV is demonstrated by the correspondence between patterns of flow curvature revealed by this method and patterns of helical motion documented at cross sections within the confluences using acoustic Doppler velocimetry. The method can also be used to characterize the structure of turbulent vortices within the mixing interface between confluent streams under appropriate conditions. Hydrodynamic mapping using sUAS‐based LSPIV enriches the interpretation of traditional in‐stream velocity data acquired in the field and provides information on surface velocity patterns in rivers at a resolution similar to that of numerical models. Key Points: sUAS‐derived LSPIV provides unprecedented spatial detail of 2‐D surface flow patterns at confluences Patterns of 2‐D surface flow at an asymmetrical and symmetrical confluence show similarities to, but also important differences from, conceptual models of flow at confluences 2‐D sUAS‐derived LSPIV can enhance interpretations of 3‐D flow measurements and yields information density comparable to that of CFD models