Tracer Study of Mixing and Transport in the Upper Hudson River with Multiple Dams

In October 2001, ,0.2 mol of SF6 was injected into the upper Hudson River, a modified natural channel with multiple dams, at Ft. Edward, N.Y. The tracer was monitored for 7 days as it moved ,50 km downriver. The longitudinal evolution of the tracer distribution was used to estimate one-dimensional advection s9.0±0.2 km d−1d and dispersion s17.3±4.0 m2 s−1d along the river axis. Comparison of these results to tracer studies on channels without dams suggests that dams reduce longitudinal dispersion below the value expected in a natural channel with the same discharge. SF6 loss through air–water gas exchange along the river and at two dams (10.7 m combined height) was estimated by observing decay in peak concentration. Losses at dams (approximately 50% per dam) were dominant. The estimated gas exchange at dams was compared to a simple model adapted from those available in literature. Small amounts of tracer were trapped in a canal segment (,5 km long) that parallels the river, where advection and dispersion were sharply reduced. DOI: 10.1061/(ASCE)0733-9372(2004)130:12(1498) CE Database subject headings: Dams; Dispersion; Hudson River; Mixing; Tracers; Water pollution; Volatization.