model calibration in marylandjune 20151 model calibration in maryland june 12, 2015
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Model Calibration in Maryland June 2015 1
Model Calibration in Maryland
June 12, 2015
Model Calibration in Maryland June 2015 2
Outline
• State Highway Administration Procedure- Gaged watersheds
- Ungaged watersheds
- Example
Model Calibration in Maryland June 2015 3
When to Calibrate
• Stream restoration project• Bridge or culvert sizing• Setting 100-yr flood plain limits with
ultimate development or any development
Model Calibration in Maryland June 2015 4
Calibration Issues
• Often overlooked for any watershed study• SHA requires that the study be within the
regional peak flow and plus one standard error.
Model Calibration in Maryland June 2015 5
Model Calibration in Maryland June 2015 6
SHA Publication
• This publication provides guidelines on which variables to adjust and the limits of adjustment
Model Calibration in Maryland June 2015 7
Frequency - years
Pea
k F
low
- c
fs
2 10 100
X
X
X
X WinTR-20 Results – before calibration
WinTR-20 Results – after calibration
Upper Limit
Regression Estimate
Calibration Target Range
Model Calibration in Maryland June 2015 8
Measured Data
• Stream gage within the watershed • Regional regression equations of stream
gage data (SHA 2010 or GISHydro 2000)
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Stream gage data
• On sites that are on same stream and with plus or minus 50% of the drainage area of the gage
• There is a procedure outlined in the manual for determining the peak flow frequency curve
Model Calibration in Maryland June 2015 10
Calibration
• If calibration is needed, use a historic event- Match hydrograph volume
- Match hydrograph peak discharge (and time of peak if possible)
• Use to second event to verify calibration- May have to change CN in order to match
hydrograph volume
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Guidance
“User should calibrate or validate the results of a WinTR-20 run against an independent source of measured data”
Model Calibration in Maryland June 2015 12
Model Calibration in Maryland June 2015 13
Calibration Procedure
• Table 4.2 suggests in the following order- Modify the Tc
• Modify n values
- Change the CN
- Change HSG due to urbanization
- Change the reach lengths• Storage at culverts
- Change the Dim hydrograph
- Rainfall duration
Model Calibration in Maryland June 2015 14
Guidance
• Change CN by ± 10 % • Modify n by ± 25 % for overland flow• Modify n by ± 50 % for shallow
concentrated and channel flow • Modify L by ± 25 % for shallow
concentrated and channel flow
Model Calibration in Maryland June 2015 15
Guidance
• Cross Section Area to ± 25% • Modify n by ± 50% for x-sections• Reach lengths by up to 30% for 1:24000
and up to to 19% for 1:2400 maps• If reach length is increased, generally the
slope will decrease• Do not adjust ARC
Model Calibration in Maryland June 2015 16
Dimensionless Unit Hydrograph Use
• Panel recommends DMV DUH in Eastern Coastal Plain. In Western Coastal Plain decide on a case-by-case basis.
Model Calibration in Maryland June 2015 17
Example Montgomery County
• DA = 3.70 Square Miles• Tc = 1.8 hours• CN = 85• Rainfall Distribution NOAA_C (Type NO_C in WinTR-20)
NOAA 14 Rainfall Amount (inch)
2-year 3.10
10-year 4.77
50-year 7.03
100-year 8.23
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Initial Results
Years RegressionEquation
(cfs)
UpperBounds
(cfs)
Win-TR20 (cfs)
2 798 1000 1329
10 1900 2300 2512
50 3230 3800 4157
100 4200 4600 5023
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Calibration Window
Model Calibration in Maryland June 2015 20
Next Step
• Modify Tc 2.0• Modify CN 80
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ResultsYears Regression
Equation(cfs)
UpperBounds
(cfs)
Win-TR20 (cfs)
2 798 1000 962
10 1900 2300 1993
50 3230 3800 3500
100 4200 4600 4313
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Calibration Window
Model Calibration in Maryland June 2015 23
The End
Model Calibration in Maryland June 2015 24
Porcupine Mountain State Park, Michigan
Model Calibration in Maryland June 2015 25
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