Time of Travel Study

The following photos depict some of the routine activities of DEQ's Water Quality Surveys personnel as they conduct a time-of-travel study on the Boeuf River. The Boeuf River is approximately 250 miles long, and runs through both Louisiana and Arkansas. The Louisiana portion of the Boeuf stretches from the Louisiana-Arkansas state line to its confluence with the Ouachita River. The time-of-travel study took place on the Upper Boeuf River. The Upper Boeuf River (for the purposes of this study) is approximately 100 miles long and goes from the Louisiana-Arkansas state line to the Bayou Lafourche Cutoff, east of the town of Oak Ridge.  

Time-of-travel studies are used to determine the rate at which a substance travels downstream and how the concentrations vary along the way.  Information from these studies may be used to determine discharge and reaeration1 potential of the water system, which are factors that will influence the system's ability to take in certain components of wastewater discharges, overland runoff, and other discharges.  

  1. Water Quality Surveys' Environmental Scientists preparing Rhodamine WT dye2 to be released into the Boeuf River. By using dye as an indicator, a particular portion, or "slug," of water can be easily tracked to allow measurement of travel time as it moves downstream.  

  2. The precise location of the dye release is recorded with a global positioning system, or GPS unit. The GPS unit will demarcate the exact location of the scientists, by establishing the latitude and longitude, to ensure accurate recording of data, etc. 
  3. In this study of the Boeuf River, dye is released from a bridge over the Boeuf River. By using this bridge for the dye release, the scientists are able to position themselves equidistant from each other. In doing so, the dye will be distributed the most equally into the waterbody at the point of release.
  4. Rhodamine WT dye is released into the waterbody as shown in this photo. Note the bright red color of the dye as it enters the Boeuf River.
  5. Moments after the dye is released into the waterbody, signs of water movement are evident. The normal flow of the river will dilute the dye and carry it downstream. After a duration of time appropriate to the flow conditions, the scientists will track the dye downstream using a fluorometer3 which measures the concentration of dye in the water at multiple points downstream from the dye release.  A GPS unit is used to locate the exact point of the leading edge of the dye cloud.  All information gathered will help to determine the time of travel of the waterbody which may be used to determine discharge and reaeration rates as well.  
     
  6. Here is another photo taken of the dye cloud in the Boeuf River. Partially due to the lack of rain this season, the flow in the Boeuf River at the time of the study was fairly sluggish. 
     
  7. The photo below shows how the dye cloud would look in a waterbody with higher flow. Note the shape of the cloud and the dilution already taking place as it moves downstream at a fairly rapid pace.  

    Please email us at deqtmdl@LA.GOV with any questions or comments.  


     

    1Diffusion is the natural process of oxygen interspersing into water when oxygen concentrations in the water are lower than that of the surrounding air. The total effect of oxygen diffusing across the air-water interface throughout the water column and over time is known as reaeration.

    2Rhodamine dye is a bright red dye, which is non-toxic to fish, wildlife, and humans and has a low tendency to stain silt, dirt, plants, and other suspended matter in fresh and salt waters.  The movement of the waterbody will cause it to disperse until it is visible only to specialized instruments.

    3An instrument containing a lamp or other means of exciting fluorescent radiation in a sample, with filters and a detector to measure relative fluorescent tendencies caused by variations in concentration of the substance under examination.

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