SF_6-~3He Tracer Release Experiment: A New Method of Determining Longitudinal Dispersion Coefficients in Large Rivers

摘要

Longitudinal dispersion coefficients have been determined in the tidal Hudson River using sulfur hexafluoride. For this purpose, SF_6, a nonreactive synthetic gas, was injected into the Hudson south of Albany, NY, and used in a fashion similar to a fluorescent dye. Three days after injection, SF_6 distributions along the main axis of the river were approximately Gaussian. The change in variance with time showed two periods of linear growth. During the first period (days 3-8), the longitudinal dispersion coefficient was estimated to be 47 ± 6 m~2 s~(-1), and during the second period (days 8-13), it was 162 ± 22 m~2 s~(-1). A second gas, ~3He, which was injected simultaneously with SF_6, allowed for the determination of gas exchange rates across the air—water interface. Gas transfer velocities normalized to a Schmidt number of 600 ranged from 2.8 to 9.2 cm h~(-1) and correlated well with mean wind speed.