Resolving two‐dimensional flow structure in rivers using large‐scale particle image velocimetry: An example from a stream confluence

Large scale particle image velocimetry (LSPIV) has emerged as a valuable tool for measuring surface velocity in a variety of fluvial systems. LSPIV has typically been used in the field to obtain velocity or discharge measurements in relatively simple one-dimensional flow. Detailed two-dimensional or three-dimensional characterization of flow structure has been relegated to laboratory settings because of the difficulty in controlling PIV limiting factors such as poor particle seeding, the need for camera rectification, and challenging field conditions. In this study we implement a low-cost LSPIV setup using a high-resolution action camera mounted above a stream confluence and water seeded with recycled landscape mulch. Time-averaged 2D velocities derived from LSPIV are compared with those measured with an acoustic Doppler velocimeter (ADV) in the camera's field of view. We also assess the capabilities of this setup to resolve both turbulent and time-averaged flow structures at a stream confluence. Our results reveal that even in challenging field conditions a basic LSPIV setup can yield accurate data on velocity and resolve in detail the temporal evolution of flow structures on the surface of rivers. The resulting dataset contains velocity information at high spatial and temporal resolution, a significant advance in understanding flow processes at stream confluences. Our LSPIV analysis provides support for previous numerical modeling studies that have distinguished between Kelvin-Helmholtz and wake modes of turbulent behavior within the mixing interface at confluences. This study shows that LSPIV should be considered as both an alternative for traditional methods and a tool that can provide unprecedented levels of resolution of surface velocity patterns on rivers that can be used to evaluate numerical predictions of flow structure in complex fluvial environments. This article is protected by copyright. All rights reserved.

[1]  B. Rhoads,et al.  Field investigation of three‐dimensional flow structure at stream confluences: 1. Thermal mixing and time‐averaged velocities , 2001 .

[2]  Ichiro Fujita,et al.  Refinement of LSPIV Technique for Monitoring River Surface Flows , 2000 .

[3]  B. Rhoads,et al.  Rates and patterns of thermal mixing at a small stream confluence under variable incoming flow conditions , 2015 .

[4]  Maurizio Porfiri,et al.  Orienting the camera and firing lasers to enhance large scale particle image velocimetry for streamflow monitoring , 2014 .

[5]  R. Moser,et al.  The three-dimensional evolution of a plane mixing layer: the Kelvin–Helmholtz rollup , 1992, Journal of Fluid Mechanics.

[6]  G. Constantinescu,et al.  Structure of turbulent flow at a river confluence with momentum and velocity ratios close to 1: Insight provided by an eddy‐resolving numerical simulation , 2011 .

[7]  Jiarong Hong,et al.  Natural snowfall reveals large-scale flow structures in the wake of a 2.5-MW wind turbine , 2014, Nature Communications.

[8]  Jérôme Le Coz,et al.  Advantages of a mobile LSPIV method for measuring flood discharges and improving stage–discharge curves , 2011 .

[9]  Iehisa Nezu,et al.  PIV and PTV measurements in hydro-sciences with focus on turbulent open-channel flows , 2011 .

[10]  Witold F. Krajewski,et al.  Experimental System for Real-Time Discharge Estimation Using an Image-Based Method , 2008 .

[11]  Marian Muste,et al.  Large‐scale particle image velocimetry for measurements in riverine environments , 2008 .

[12]  B. Rhoads,et al.  Spatial and temporal structure of shear layer turbulence at a stream confluence , 2004 .

[13]  William J. Plant,et al.  measuring stream discharge by non‐contact methods: A Proof‐of‐Concept Experiment , 2000 .

[14]  R. Adrian.  Particle-Imaging Techniques for Experimental Fluid Mechanics , 1991 .

[15]  William Thielicke,et al.  PIVlab – Towards User-friendly, Affordable and Accurate Digital Particle Image Velocimetry in MATLAB , 2014 .

[16]  J. F. Fox,et al.  Large-scale eddies measured with large scale particle image velocimetry , 2008 .

[17]  Stuart Cameron,et al.  PIV algorithms for open-channel turbulence research: Accuracy, resolution and limitations , 2011 .

[18]  B. Rhoads,et al.  Field investigation of three‐dimensional flow structure at stream confluences: 2. Turbulence , 2001 .

[19]  G. Constantinescu,et al.  Numerical analysis of the effect of momentum ratio on the dynamics and sediment-entrainment capacity of coherent flow structures at a stream confluence , 2012 .

[20]  W. Uijttewaal,et al.  Development of quasi two-dimensional structures in a shallow free-surface mixing layer , 1998 .

[21]  Ichiro Fujita,et al.  Application of aerial LSPIV to the 2002 flood of the Yodo River using a helicopter mounted high density video camera , 2011 .

[22]  Anton J. Schleiss,et al.  Large-scale PIV surface flow measurements in shallow basins with different geometries , 2009, J. Vis..

[23]  R. Adrian.  Twenty years of particle image velocimetry , 2005 .

[24]  PIV study of the influence of large-scale streamwise vortices on a turbulent boundary layer , 2002 .

[25]  Ichiro Fujita,et al.  Unseeded and seeded PIV measurements of river flows videotaped from a helicopter , 2003, J. Vis..

[26]  G. Taylor.  The Spectrum of Turbulence , 1938 .

[27]  Carl D. Meinhart,et al.  Vortex organization in the outer region of the turbulent boundary layer , 2000, Journal of Fluid Mechanics.

[28]  Anton Kruger,et al.  Large-scale particle image velocimetry for flow analysis in hydraulic engineering applications , 1998 .

[29]  Anton Schleiss,et al.  LSPIV implementation for environmental flow in various laboratory and field cases , 2011 .

[30]  S. Socolofsky,et al.  Experiments on Mass Exchange between Groin Fields and Main Stream in Rivers , 2008 .

[31]  A. Melling.  Tracer particles and seeding for particle image velocimetry , 1997 .

[32]  A. Roy,et al.  1 min in the life of a river: selecting the optimal record length for the measurement of turbulence in fluvial boundary layers , 2005 .

[33]  Volker Weitbrecht,et al.  Large scale PIV-measurements at the surface of shallow water flows , 2002 .

[34]  A. Roy,et al.  Bed morphology and sedimentology at the confluence of unequal depth channels , 1993 .

[35]  B. Rhoads,et al.  Flow structure at an asymmetrical stream confluence , 1995 .

[36]  Numerical evaluation of the effects of planform geometry and inflow conditions on flow, turbulence structure, and bed shear velocity at a stream confluence with a concordant bed , 2014 .

[37]  Marian Muste,et al.  Validation and Extension of Image Velocimetry Capabilities for Flow Diagnostics in Hydraulic Modeling , 2004 .

[38]  Hao-Che Ho,et al.  Considerations on direct stream flow measurements using video imagery: Outlook and research needs , 2011 .

[39]  Anton Kruger,et al.  Flow measurement in streams using video imagery , 2002 .

[40]  B. Rhoads,et al.  Time-averaged flow structure in the central region of a stream confluence , 1998 .

[41]  J. Lasheras,et al.  On the origin and evolution of streamwise vortical structures in a plane, free shear layer , 1986, Journal of Fluid Mechanics.

[42]  Guillaume Dramais,et al.  Performance of image-based velocimetry (LSPIV) applied to flash-flood discharge measurements in Mediterranean rivers. , 2010 .

[43]  B. Rhoads,et al.  Lateral momentum flux and the spatial evolution of flow within a confluence mixing interface , 2008 .

[44]  André Paquier,et al.  Application and evaluation of LS-PIV technique for the monitoring of river surface velocities in high flow conditions , 2008 .