Stream velocity and dispersion characteristics determined by dye-tracer studies on selected stream reaches in the Willamette River Basin, Oregon

Abstract Dye-tracer analyses were done in the Willamette River and nine tributaries of the Willamette River, from April 1992 to July 1993 during low to medium stream discharge conditions, to determine velocity and dispersion. These dye-tracer analyses provided information on time of arrival, peak concentration, and the occurrence and longevity of a constituent dissolved in streamflow at various discharges. The time of travel of the peak and leading and trailing edge of the dye cloud were determined for each stream segment and were related to discharge at an index location in each stream. On the basis of the dye-tracer measurements, an equation was developed to estimate the velocity of the peak of a solute cloud for unmeasured streams. The results of the dyetracer study on theWillamette River from river mile 161.2 to river mile 138.3 were compared with a previous study of the same river reach. The results of the comparison indicate that, since 1968, the discharge velocity relation has not changed in the streamflow range observed in this study. In order to identify dyedispersion characteristics of a conservative solute in each stream segment, a relation was developed between the elapsed time from injection to the unit-peak concentration of dye measured at each sampling location. A general equation was developed to estimate the peak concentration of dye at a given elapsed time. Channel characteristics and streamflow magnitude are known to effect dye dispersion; however, comparison of streams with apparently similar characteristics resulted in different unit-peak concentration values at various times after dye injection.