Evaluating Water Quantity and Water Quality Issues in Illinois Streams Using Large-Scale Particle Image Velocimetry (LSPIV)

First, in relation to measurements of river discharge, the performance of the tripod-mounted LSPIV and the UAS LSPIV was nearly identical in each case where both methods were used. We found that when the tripod is extended high enough to view the entire channel width, the camera oscillates in the wind. The UAS is also not completely steady, but after about 30 seconds (depending on wind speed and height above the water surface), mean velocities are generally unaffected by camera movement. While in certain situations, such as in narrow, tree-lined rivers, in restricted flight zones, or when no certified UAS operator is present, it may be beneficial to use a tripod-mounted camera, in many situations the UAS is a more flexible option for obtaining mean surface velocity and therefore discharge. The UAS can more easily image wide rivers and the field of view can be adjusted on the fly in response to changing conditions. In addition, LSPIV discharge from both the tripod and UAS compared favorably with the propeller and ADCP discharge and were often within a few percent of these reference values. Our results generally support the typical practice of relating depth-averaged velocity to surface velocity with a simple coefficient in the range of 0.85 — 0.9, but additional research into this is ongoing. Finally, we found that in some low and high flow conditions, the LSPIV discharge was close to the reference discharges measured by the research team but significantly (>25 %) different than the USGS gage. Overall, both the tripod and UAS methods resulted in rapid, accurate discharge calculations with respect to reference methods. Second, we found that LSPIV is an important complement to traditional velocity measurements and can enrich our understanding of flow in complex hydrodynamic environments like confluences. Not only can LSPIV be used for qualitative flow visualization, useful for comparison among field sites and flow events and with numerical modeling, but quantitative information can be obtained over a large spatial scale. UAS greatly increases the capability to obtain LSPIV over a large area, and mean flow velocities are relatively easy to obtain. It is generally more difficult to obtain quasi-instantaneous flow “snapshots”, especially as camera height above the water and magnitude of camera movement/oscillation increases. Under favorable circumstances, however, flow snapshots can be obtained from both tripod mounted and UAS LSPIV.