Cohstrex: Coherent Structures in Rivers and Estuaries Experiment
Coherent Flow Structures at Earth's Surface
Remote sensing, Thermal signatures
COHSTREX, the Coherent Structures in Rivers and Estuaries Experiment, was a five-year project to exploit the remotely sensed signatures of coherent flow structures in rivers and estuaries. The purpose of the study was to use remote-sensing measurements of coherent structures at a river surface to characterize and quantify the flow. Two major field experiments were undertaken on the Snohomish River near Everett, WA, United States. The first experiment took place near the mouth of the river where stratification was strong due to a tidally driven salt wedge. Flow over a rocky sill generated a field of boils (bottom-generated fluid upwellings) on the flow surface that propagated downstream and provided insight into mixing layer dynamics. The second experiment took place approximately 15[t#]km upstream from the mouth of the river where the tide still affected the river level and velocity, but stratification was minimal. The focus of the unstratified flow experiment was the study of boils generated by flow over flat beds and beds with a bottom roughness. Herein, we provide an overview of infrared measurements of thermal variability on the surface and in-situ measurements of turbulent velocities beneath the surface. A major finding of COHSTREX is that infrared imagery of the thermal signature of coherent flow structures in estuarine rivers is a powerful tool for visualizing and quantifying the flow. Thermal signatures include mixing of water masses with different temperatures, and disruptions of the flow surface by coherent flow structures generated by bottom roughness. Through use of particle image velocimetry (PIV) techniques applied to infrared imagery of the river surface, we are able to estimate mean and turbulent properties of the flow.
Jessup, A. T., Chickadel, C. C., Talke, S. A. and Horner-Devine, A. R. (2013) Cohstrex: Coherent Structures in Rivers and Estuaries Experiment, in Coherent Flow Structures at Earth's Surface (eds J. G. Venditti, J. L. Best, M. Church and R. J. Hardy), John Wiley & Sons, Ltd, Chichester, UK.