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Salt Dilution as an Alternative Stream Discharge Measurement Technique

Explore the benefits of using salt dilution as a stream discharge measurement method, covering methodology, tracers, injection techniques, and advantages over current meter methods. Salt dilution provides a reliable and cost-effective solution for various flow conditions.

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Salt Dilution as an Alternative Stream Discharge Measurement Technique

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  1. Salt DilutionAn Alternative Stream Discharge Measurement Technique Shawn Florio, PE ADOT/PF Quarterly Design Meeting February 6, 2007

  2. Discussion Topics • Standard Discharge Techniques • Tracer Dilution Rationale • Methodology • Examples

  3. Standard Discharge Methods • Current Meter • Velocity-Area Method • Acoustic Doppler • Tracer Dilution

  4. Current Meter(Velocity-Area Method) Reference: USGS Water-Supply Paper 2175, 1982

  5. What’s wrong with the current meter method? • Nothing really… • It is a preferred method in laminar flows that can be safely waded Laminar flow

  6. Turbulent Flow Turbulent streams violate the assumption of laminar flow for current meter measurements

  7. Shallow, Turbulent Flow

  8. Dangerously High Flow Conditions

  9. Salt Dilution Rationale • Alternative to Current Meter • A USGS Standard Method • Practical For Very Low or High (Dangerous) Flows • Complementary to Current Meter • Turbulence is preferred • Good Mixing Required

  10. Tracers • Common Tracers • Rhodamine WT Dye • Common Table Salt • Advantages of Salt • Inexpensive & Readily Available • Field Measurements Possible • Electrical Conductivity Meter • Non-Toxic For Typical Concentrations & Exposure Times

  11. Injection Methods • Constant Rate Injection • Requires More Complex Equipment Setup • Pump Or Marionette Flask • Limited To Low Flows (<100 cfs) In Bush • Due To Volume Of Injection Solution Needed • Slug Injection • Instantaneous Injection Of Known Tracer Mass • No Special Equipment Required • Can Be Used For Higher Flows

  12. Salt Dilution Methodology • Determine Injection Location Upstream Of Measurement Point • 20 to 25 Channel Widths • Add Known Mass Of Salt • 1 lb per 9 cfs • Increase Conductivity 100- 200% • 400 uS/cm Reported Causing Incidental Drift (Weikel, 2005) • Observe/Record Concentration Curve

  13. Conductivity Time Highly turbulent flow Less turbulent flow Basic Theory Add known quantity of tracer and observe conductivity downstream at a point where flow is completely mixed.

  14. Calibration Factor (CF) Relates Conductivity to Concentration Specific To Stream Chemistry & Temperature

  15. On-Site Calibration Preferred

  16. Effect Of Mixing Length 300 ft upstream 400 ft upstream

  17. Summary • Provides Alternative to Current Meter • Steep, Turbulent Streams • Shallow, Low Flows • Dangerously High Flows • Complementary Conditions To Current Meter • Safe, Inexpensive, & Easy To Use • Provides Reliable Results

  18. References • Hudson, R. and J. Fraser. 2002. Alternative methods of flow rating in small coastal streams. B.C. Ministry of Forests, Vancouver Forest Region, Nanaimo, BC.Extension Note EN-014 Hydrology. 11 p. • Hudson, R and J. Fraser. 2005. Introduction to Salt Dilution Gauging for Streamflow Measurement Part IV: The Mass Balance (or Dry Injection) Method. Streamline Watershed Management Bulletin Vol. 9/No. 1. 6 p. • Weikel, J., J. Clinton and J. Cathcart. 2005. Monitoring Protocol for Reporting Impacts of the Salt Tracer Methodology on Stream Biota. Forest Health and Monitoring Unit Private and Community Forests Program Oregon Department of Forestry Salem, OR. • Moore, R.D. 2004a. Introduction to salt dilution gauging for streamflow measurement: Part 1. Streamline Watershed Management Bulletin 7(4):20–23. • Moore, R.D. 2004b. Introduction to salt dilution gauging for streamflow measurement Part II: Constant-rate injection. Streamline Watershed Management Bulletin 8(1):11–15. • Moore, R.D. 2005. Introduction to salt dilution gauging for streamflow measurement Part III: Slug injection using salt in solution. Streamline Watershed Management Bulletin 8(2):1–6. • Perkins, T. and J. Cathcart. 2006. Salt Dilution Gauging Procedure. Technical Memo from Knight Piesold to HDR Alaska.

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