Stream velocities and reaeration coefficients for the South Umpqua River between Tiller and Roseburg, Oregon, 1991

Abstract

Dye-tracer and gas-tracer studies were done in July and September, 1991, during low flows on four reaches of the South Umpqua River between Tiller and Roseburg, Oregon. For a streamflow of 435 ft 3 /s (cubic feet per second) at the Brockway streamflow monitoring site (14312000) at river mile 132.7, the average stream velocity between Tiller and Myrtle Creek is estimated at 0.88 ft/s (feet per second), and between Myrtle Creek and Roseburg is estimated at 0.64 ft/s. For a streamflow of 129 ft 3 /s at the Brockway site, the average stream velocity between Tiller and Myrtle Creek is estimated at 0.34 ft/s, and between Myrtle Creek and Roseburg is estimated at 0.23 ft/s. For a streamflow of 129 ft 3 /s at the Brockway site, the reaeration coefficients determined from gasdesorption data collected in the selected reaches for this study ranged from 1.03 to 8.35 per day. The reaeration coefficients determined for this study were approximately two times larger than values derived from a semiempirical formula that uses variables of mean velocity and slope, but confirmed a conceptual formula that uses variables of mean velocity and average depth. Average stream-reach velocity, width, depth, and slope data that were used to compute reaeration coefficients were collected during this study.