Watershed Slope Lower Bounds for Methods EWRI-2012 21 MAY 2012.
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Transcript of Watershed Slope Lower Bounds for Methods EWRI-2012 21 MAY 2012.
![Page 1: Watershed Slope Lower Bounds for Methods EWRI-2012 21 MAY 2012.](https://reader035.fdocuments.net/reader035/viewer/2022070415/56649f115503460f94c248ae/html5/thumbnails/1.jpg)
Watershed Slope Lower Bounds for Methods
EWRI-2012 21 MAY 2012
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Acknowledgements
• Texas Department of Transportation; “0-6384 Establish Effective Lower Bounds of Watershed Slope for Traditional Hydrologic Methods”
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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.
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Why does slope matter?
• Magnitude
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Why does slope matter?
• Direction
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Rainfall Intensity
Rainfall Intensity
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Why does slope matter?
• Losses/Storage
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Why does slope matter?
• Drainage channel has capacity – but water “slow” to get there.
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Why does slope matter?
• Simple expression of time in terms of speed and distance
• Expression for time in hydrology
€
T =X
V
€
T =nαLβ
iγSδ
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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.
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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
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Defining Low Slope
• Literature interpretation
€
S < 0.5%
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Low Slope Alternate Methods
• Experiments– Rainfall simulator– Small plot – paved– Small plot – grass
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Low Slope Alternate Methods
• Small Plot “Paved”
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Low Slope Alternate Methods
• Small Plot – “Grass”
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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
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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.
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Low Slope Alternate Methods
• Experimental Data Interpretation– Literature Studies
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Low Slope Alternate Methods
• Experimental Data Interpretation– Literature Studies
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Low Slope Alternate Methods
• Experimental Data Interpretation– Our Experiments
0.000
0.005
0.010
0.015
0.020
0.025
0.030
Dis
char
g e (
cfs )
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Rai
nfal
l (in
/ hr)
0.0 3.0 6.0 9.0 12.0 15.0Time (hr)
0.0 3.0 6.0 9.0 12.0 15.0
Discharge (Observed)Discharge (Simulated)
Rainfall
Rainfall intensity and discharge flow rate (Concrete Plot, 0911~12-5 min Data, Diffusion Approximation)
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Low Slope Alternate Methods
• Parametric Study
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20
Dis
char
g e (
cfs )
0
5
10
15
20
25
30
35
40
Rai
nfal
l (in
/ hr)
0 30 60 90 120 150 180Time (min)
0 30 60 90 120 150 180
T3-S1 (S=10%)T3-S2 (S=5%)T3-S3 (S=1%)T3-S4 (S=0.1%)T3-S5 (S=0.05%)T3-S6 (S=0.01%)T3-S7 (S=0%)
Rainfall
T1-S: Discharge Variation for Different Bed Slope(Plot Length=1000 ft, Width=2 ft , Rainfall=3.5in/hr, Manning's n=0.02)
Rainfall =3.5 in/hr
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Low Slope Alternate Methods
• Parametric Study
1
10
100
1000
0.000001 0.00001 0.0001 0.001 0.01 0.1 1
Tc (m
inut
es)
Slope
Simulated by DHMRegression for S > 0.0005Regression S > 0.003
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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
€
T =nαLβ
iγ (S + SLB )δ
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Low Slope Alternate Methods
• Impermeable surfaces– Low slope starts at 0.005
€
T = (1.612 −1.196S
SLB + S)(
n0.6175L0.551
i0.388(S + SLB )0.436)
€
SLB = 0.0005
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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.
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Aggregate Observational Database
• 100+ watersheds– Low and
moderate slopes– Small and large
areas– All plot along
similar pattern except for two.
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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
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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)