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 stream flow of 435 cubic feet per second at the Brockway streamflow monitoring site (14312000), the average stream velocity between Tiller and Myrtle Creek is estimated at 0.88 feet per second, and between Myrtle Creek and Roseburg is estimated at 0.64 feet per second. For a streamflow of 129 cubic feet per second at the Brockway site, the average stream velocity between Tiller and Myrtle Creek is estimated at 0.34 feet per second, and between Myrtle Creek and Roseburg is estimated at 0.23 feet per second. For a streamflow of 129 cubic feet per second at the Brockway site, the reaeration coefficients determined from gas-desorption 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 using a semiempirical formula and at least five times larger than the values derived using a conceptual formula. Average stream-reach velocity, depth, and slope data that were used to compute reaeration coefficients were collected during this study. Reaeration coefficient formulas developed for the South Umpqua River between Tiller and Roseburg are presented in this report.
