Model Calibration in Maryland June 2015 1

Model Calibration in Maryland

June 12, 2015

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Outline

• State Highway Administration Procedure- Gaged watersheds

- Ungaged watersheds

- Example

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When to Calibrate

• Stream restoration project• Bridge or culvert sizing• Setting 100-yr flood plain limits with

ultimate development or any development

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Calibration Issues

• Often overlooked for any watershed study• SHA requires that the study be within the

regional peak flow and plus one standard error.

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Model Calibration in Maryland June 2015 6

SHA Publication

• This publication provides guidelines on which variables to adjust and the limits of adjustment

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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

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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

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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”

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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

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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

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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

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Dimensionless Unit Hydrograph Use

• Panel recommends DMV DUH in Eastern Coastal Plain. In Western Coastal Plain decide on a case-by-case basis.

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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

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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

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The End

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Porcupine Mountain State Park, Michigan

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