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“Water Discharge Using Salt Tracer and Area-Velocity”

“Water Discharge Using Salt Tracer and Area-Velocity”. Catherine Riihimaki, Drew University criihimaki@drew.edu. Salt Tracer Discharge. Area-Velocity Discharge. 1. Dump salt upstream. 2. Measure electrical conductivity downstream. Goals of assignment:

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“Water Discharge Using Salt Tracer and Area-Velocity”

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  1. “Water Discharge Using Salt Tracer and Area-Velocity” Catherine Riihimaki, Drew University criihimaki@drew.edu

  2. Salt Tracer Discharge Area-Velocity Discharge 1. Dump salt upstream 2. Measure electrical conductivity downstream

  3. Goals of assignment: • Students learn basic plotting in KaleidaGraph • Excel can work too, but K-Graph can integrate curve automatically • We use K-Graph later in course because it has more options for complex curve-fitting • Students learn some calculation tools in K-Graph (or return to visual integration) • Students have opportunity to observe stream characteristics • Students can compare strengths and weaknesses of two field techniques • Students think about conservation of mass

  4. Rearrange… The background Reach of stream of length L and discharge Q Ms: added mass of salt at upstream end C0: background concentration C1: new concentration due to the addition of Ms QC0: background rate of mass transport of salt (in kg/s) QC1: background plus additional mass transport due to the added tracer Over a time of observation T: Incoming mass of salt naturally plus added mass of salt equals the mass leaving the reach

  5. Solve for Q The background Convert concentration to electrical conductivity E using conversion factor F

  6. The background

  7. Procedures: • Introduce conservation of mass • Introduce salt tracer method • Go into field for measurements (1 50-minute class) • Need 1 salt dumper • 2-3 people per measurement team (measurer, timer, recorder) • Record every 10-30 seconds (background through peak back to background) • All or some do area-velocity measurements • Students work independently out of class on calculations • Students complete a lab write-up with graphs

  8. Why this activity: • Many of the students have done area-velocity measurements, but not salt tracer • Wading is not necessary unless area-velocity calculations are done concurrently • Good opportunity for methodology comparison • The students will have some measure of skepticism that the procedure will work until they do the calculations • Portability: • Need electrical conductivity meter(s), bucket, salt • Can use both methods or just replace area-velocity method in your discharge lab • Try it yourself first!

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