Field Observations of Longitudinal Dispersion in a Run-Of-The-River Impoundment

Abstract Dye studies were conducted on a run-of-the-river impoundment to observe longitudinal dispersion in a lacustrine/riverine environment. Field data were analyzed in the context of a streamtube model which accounts for dispersion by the lateral distribution of longitudinal velocity. The differential advection associated with the vertical distribution of longitudinal velocity [i.e. Elder's equation ( D x = α x u ∗ h )] is incorporated in this stream-tube model providing longitudinal dispersion within each tube. Model calibration attempts required α values on the order of 100, greatly in excess values expected from fluvial experience. A diffusive stall was observed twice when the dye plume moved into a sudden expansion of channel width. The stall is predicted by Fischer's K x equation. The stream-tube model reasonably reproduced the field data in a variety of initial-period conditions, caused by the highly variable geometry of Coralville Reservoir.