Travel times and dispersion of soluble dye in thirteen New Hampshire rivers

Abstract

Dye was injected and traced in 13 New Hampshire rivers in 2000 to determine the velocity at which a soluble substance spilled into the river would travel to drinking-water supply intakes. Travel times were studied on the Ammonoosuc, Androscoggin, Connecticut, Contoocook, East Branch Pemigewasset, Exeter, Lamprey, Mascoma, Merrimack, Oyster, Piscassic, Salmon Falls, and Sugar Rivers. Dye was injected and sampled at low and mean flows, and the measured velocities extrapolated to provide an estimate of the velocity during a mean annual flood (mean of yearly peak flows for a specific river). Rivers were sampled downstream of the dye-injection sites to measure dye concentrations and the arrival and passage times of the dye cloud. This information was used to estimate a relation between river discharge and the expected dye concentrations and velocities for each river. Results of the dye tests were used to estimate a 6-hour travel distance at mean annual flood for each of the 13 rivers, and to create graphical relations that can be used to estimate the travel times and concentrations of solutes over a range of river discharges and distances. Observed transport velocities ranged from 0.03 to 2.4 feet per second, and the estimated 6-hour travel distances ranged from 5.8 to 43 miles. Rivers in upland areas had the highest velocities, whereas rivers in the low coastal region had the slowest velocities.