Flow Measurements with Fluorescent Tracers

Laboratory studies were conducted to obtain information relative to the accuracy and precision with which fluorescent tracers can be used to determine stream discharge. Field-scale comparisons are difficult because the tracer technique is potentially capable of higher accuracies than other large-scale field measurement methods presently available. The laboratory studies show that accurate stream flow measurement of ± 1% to 2% can be obtained if the effects of imperfect lateral mixing and tracer losses to the channel boundaries are reduced to negligible amounts. Reliable criteria for guaranteeing adequate lateral mixing require further study. The sampling technique indicates whether mixing was adequate, but this is after-the-fact and deserves improvement. Data indicate that the effects of tracer losses to the stream boundaries may be negligible.