Model Calibration in MarylandJune 20151 Model Calibration in Maryland June 12, 2015.

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)

Model Calibration in Maryland June 2015 9

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

Model Calibration in Maryland June 2015 11

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

Model Calibration in Maryland June 2015 18

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

Model Calibration in Maryland June 2015 19

Calibration Window

Model Calibration in Maryland June 2015 20

Next Step

• Modify Tc 2.0• Modify CN 80

Model Calibration in Maryland June 2015 21

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

Model Calibration in Maryland June 2015 22

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