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Watershed Slope Lower Bounds for Methods. EWRI-2012 21 MAY 2012. Acknowledgements. Texas Department of Transportation; “0-6384 Establish Effective Lower Bounds of Watershed Slope for Traditional Hydrologic Methods”. Project Team. Theodore G. Cleveland - Texas Tech University

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Presentation Transcript
acknowledgements
Acknowledgements
  • Texas Department of Transportation; “0-6384 Establish Effective Lower Bounds of Watershed Slope for Traditional Hydrologic Methods”
project team
Project Team
  • Theodore G. Cleveland - Texas Tech University
  • Ming-Han Li – Texas A&M University
  • William H. Asquith – USGS
  • Xing Fang – Auburn University
  • David B. Thompson – R.O. Anderson Inc.
slide6

Rainfall Intensity

Rainfall Intensity

why does slope matter3
Why does slope matter?
  • Drainage channel has capacity – but water “slow” to get there.
why does slope matter4
Why does slope matter?
  • Simple expression of time in terms of speed and distance
  • Expression for time in hydrology
why does slope matter5
Why does slope matter?
  • Consequences of “slope” in denominator
    • As slope vanishes time becomes huge.
    • Huge time impacts intensity estimate.
    • Huge time impacts unit hydrograph behavior.
what we did
What we did
  • Defined low slope
    • Literature interpretation
    • Experiments (Physical and Numerical)
  • Developed alternative methods
    • Parametric study using numerical model
    • Created an “adjustment” for low-slope hydrology
  • Developed plan for future monitoring
    • Emerging technologies needed
defining low slope
Defining Low Slope
  • Literature interpretation
low slope alternate methods
Low Slope Alternate Methods
  • Experiments
    • Rainfall simulator
    • Small plot – paved
    • Small plot – grass
low slope alternate methods1
Low Slope Alternate Methods
  • Small Plot “Paved”
low slope alternate methods2
Low Slope Alternate Methods
  • Small Plot – “Grass”
low slope alternate methods3
Low Slope Alternate Methods
  • Experiment Purpose
    • Obtain data for validating a computer model
    • Computer model used for the parametric study to develop guidelines for low-slope hydrologic computations.
  • Experiment Summary
    • Simulator slopes range from 0 to 5%
    • Field slopes are 0.25% (0.0025)
    • Paved, grass, bare-earth surfaces represented
low slope alternate methods4
Low Slope Alternate Methods
  • Experimental Data Interpretation
    • Diffusion-Hydrodynamic-Model (DHM) to interpret experimental results
    • Use DHM to examine behavior in a parametric study to develop alternative estimation tools.
low slope alternate methods5
Low Slope Alternate Methods
  • Experimental Data Interpretation
    • Literature Studies
low slope alternate methods6
Low Slope Alternate Methods
  • Experimental Data Interpretation
    • Literature Studies
low slope alternate methods7
Low Slope Alternate Methods
  • Experimental Data Interpretation
    • Our Experiments
low slope alternate methods10
Low Slope Alternate Methods
  • Additional support for where “low slope” begins – about 0.5% or smaller
  • Use the DHM to investigate alternate method for time in hydrologic models
low slope alternate methods11
Low Slope Alternate Methods
  • Impermeable surfaces
    • Low slope starts at 0.005
low slope alternate methods12
Low Slope Alternate Methods
  • Permeable surfaces
    • Low slope starts at 0.005
    • A unified general equation could not be found, instead three based on dominant soil type
    • Mathematical structure same, exponents are different by soil, the offset lower bound is the same.
aggregate observational database
Aggregate Observational Database
  • 100+ watersheds
    • Low and moderate slopes
    • Small and large areas
    • All plot along similar pattern except for two.
monitoring plan
Monitoring Plan
  • Discovered that current measurement technologies are not low-slope compatible.
    • Use existing culverts as gaging stations, should the need arise.
    • Emergent (low-cost) technologies that can make the measurements in low-slope conditions
      • Laser and reflective targets
      • Visible/IR image interpretation
      • Pressure sondes
conclusions
Conclusions
  • Defined low slope, about 0.3% and smaller.
  • Alternative timing model to use in such conditions.
  • Emerging technology needs to be deployed to measure discharges on low slope.
  • Guidance in final report on how to use these findings. (available July 2012)