Watershed slope lower bounds for methods
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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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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.




Rainfall Intensity

Rainfall Intensity


Why does slope matter2
Why does slope matter?

  • Losses/Storage


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 methods8
Low Slope Alternate Methods

  • Parametric Study


Low slope alternate methods9
Low Slope Alternate Methods

  • Parametric Study


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)


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