Knowledge Bank

Time-of-travel studies using rhodamine dye are often performed in streams to determine parameters pertinent to hydraulic modeling. New technologies for determining the concentration of the dye in-situ are being developed by Yellow Springs Instruments, Incorporated (YSI). The goal of this study was to evaluate the new in-situ probes in comparison with the industry-standard conventional field fluorometer and determine whether these new probes sufficiently captured the dye plume. Dye was injected into the Big Walnut Creek and Alum Creek in Central Ohio. Grab samples of stream water were taken from bridges downstream and evaluated using a Turner Instruments fluorometer. Simultaneously, YSI datasondes with rhodamine sensors were installed in the stream and continuously logged the concentration. The time-of-travel studies were performed under high and low flow conditions. It was determined that the YSI continuous sampler performed well once a background level was subtracted from the data. However, the background level to subtract would not be known unless a conventional fluorometer was also used. This background may be due to interference caused by algae concentrations in the stream and possibly some turbidity impacts. Therefore, the optical filter used by the YSI sensors in this study must be tuned specifically for rhodamine in order for reliable hydraulic information to be obtained from the sensor.