Stream Velocity and Dispersion Characteristics Determined by Dye-Tracer Studies on Selected Stream Reaches in the Willamette River Basin, Oregon
By Karl K. Lee
USGS Water-Resources Investigations Report 95-4078, 39 pages, 22 figures, 12 tables
Dye-tracer analyses were done in the Willamette River and nine tributaries of the Willamette River during low to medium stream-discharge conditions, from April 1992 to July 1993, to determine velocity and dispersion. These analyses helped answer questions regarding time of arrival, peak concentra-tions, and persistence of constituents dissolved in the flow for various stream discharges. The time of travel of the peak and leading and trailing edge of the dye cloud was determined for each stream segment studied, and was related to discharge at an index location for each stream. An equation was developed, based on the dye-tracer measurements, to estimate the velocity of the peak of a solute cloud for unmeasured streams. The results of the dye-tracer study on the Willamette River from river mile 161.2 to river mile 138.3 were compared with results from a previous study of the same river reach, and the results indicated that the velocity regime in the low and medium flow range has not changed since 1968. To identify the dispersion characteristics of a conservative solute in each stream segment, a relation was developed between the elapsed time from injection to the peak concentration measured at each sampling location. A general equation was developed to estimate the unit-peak concentration for a given elapsed time after a solute was introduced to the stream.
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