R. E. Rathbun H. W. Lowham Daniel P. Bauer 1979 Measurements were made along a 58-mile reach of the Yampa River in Colorado and a 77-mile reach of the Little Snake River in Colorado and Wyoming to determine traveltime, unit-concentration , and longitudinal-dispersion characteristics. Two traveltime, unit-concentration, and dispersion analyses were made along the Yampa River when its average streamflow was approximately 100 and 3,400 cu ft/s; three traveltime, unit-concentration, and dispersion analyses were made along the Little Snake River when its average streamfow was approximately 200, 600, and 1,600 cu ft/s. Reaeration coefficients were determined only for the Yampa River, when its average streamflow was approximately 100 cu ft/s. Traveltime and unit-concentration simulations were made using a mathematical model. Data collected for the Little Snake River when the average streamflow was approximately 600 cu ft/s were used as a check of model-simulation accuracy. Traveltime simulations compared to within 5%, and unit-concentration simulations were within 30 to 40% of the measured flow data. Longitudinal-dispersion coefficients ranged from 400 to 6,050 sq ft/s for the two streams. Reaeration coefficients for the Yampa River, adjusted to 20 degrees celsius, ranged from 6.04 to 33.4 per day. Two semi-empirical equations gave reaeration coefficients in best agreement with measured reaeration coefficients. Absolute errors of estimate for these equations were 11.8 and 17.3%. (USGS) application/pdf 10.3133/wri78122 en U.S. Geological Survey, Water Resources Division, Traveltime, unit-concentration, longitudinal-dispersion, and reaeration characteristics of upstream reaches of the Yampa and Little Snake Rivers, Colorado and Wyoming reports