Accumulations of woody debris along bridge piers can cause localized scour of the streambed, which can compromise the structural integrity of the bridge and increases the likelihood of catastrophic failure. In-stream flow deflecting structures are a form of debris mitigation, and they work by deflecting debris-carrying flows away from piers so that they may pass unobstructed through the bridge. The efficacy of these structures has previously been demonstrated primarily through flume experiments; however, there is little field-based testing of these structures, and descriptions of the hydrodynamic and geomorphological interactions these structures induce in field settings are scarce. We investigated the use of an Acoustic Doppler Current Profiler (ADCP) and Large-Scale Particle Image Velocimetry (LSPIV) to monitor these interactions following the construction of flow-deflecting vanes in a large, urban river in Middletown, Ohio. We observed how the locations of greatest scour transitioned away from the banks and piers as a result of the construction process. Additionally, we found that the vanes increased flow velocities in the spans between piers and decreased velocities at the piers, which suggests proper deflection from these structures. However, we noted that the vanes had a weaker influence on flow patterns during high-flow events, which suggests that the functioning of these vanes are highly dependent on channel stage. Overall, we found our results from LSPIV to correlate well with our results from the ADCP, which suggests that LSPIV can serve as a low-cost alternative to ADCP for streamflow investigations.