Flood Hydrology - ctt.mtu.edu · • Statistical Analysis of USGS Gage Data (Gage) • Statistical Models for Estimating Flow Characteristics of Michigan Streams (Regression)

Flood Hydrologyfor

Michigan Watercourses

Michigan Hydrologic Methodologies• FEMA Flood Insurance Study (FIS)• Statistical Analysis of USGS Gage Data (Gage)• Statistical Models for Estimating Flow Characteristics of Michigan

Streams (Regression)• Drainage Area Ratio (DAR)• Michigan’s Modified SCS Method (SCS)• NRCS TR-55 (TR-55)• USACE HEC-HMS (HMS)

Delineate Watershed• Watersheds

delineated in GIS• PDF map or

shapefile provided upon request

Select Method

Flood Insurance Study• Current and historical studies

available from FEMA Map Service Center: msc.fema.gov

• FEMA offers subscription for notification of new/updated studies

• FIS used when available

USGS Gage Analysis• 193 continuously-recording gages

in Michigan• 452 total gages (operating and

discontinued) in Michigan• Data available at

waterdata.usgs.gov• Data searchable by various

parameters

USGS Gage Analysis• 30 peaks for statistical analysis• 20 peaks sufficient in some cases• Longer records preferable• Gage extension• HEC-FFA used for HSDSU analysis• PeakFQ available from USGS

Regression Analysis• Methodology published in Statistical Models for Estimating Flow

Characteristics of Michigan Streams, USGS, 1984• Methodology based on gage analyses• Data published for each studied gage• Ungaged watersheds with DA>20 square miles• Flow adjustment may be applied• NSS available free from USGS

Regression AnalysisInput parameters for Regression method:

• (Contributing) Drainage Area• Slope• Channel Swamp• Slenderness Ratio• Precipitation• Soil Characteristics (geology)

Drainage Area Ratio• Calculate flows based on “known” location• Exponent 0.89• Valid 0.5 to 2.0 times drainage area

SCS Analysis• Methodology published in Computing Flood Discharges for Small

Ungaged Watersheds, MDEQ, rev. 2010• Applies to watersheds up to 20 square miles• Time of concentration >1.0 hour• Underlying methodology is rainfall-runoff unit hydrograph

methodology• Michigan methodology developed using Michigan gages

SCS AnalysisInput parameters for SCS method:

• (Contributing) Drainage Area (DA)• Ponding Adjustment• Time of Concentration (Tc)• Runoff Curve Number (RCN)• Precipitation











SCS Analysis

SCS Analysis

SCS Analysis

SCS Analysis

TR-55 Analysis• Free software available from USDA• Used when Tc<1.00 hour• State-specific dimensionless unit hydrograph• DA, Tc, RCN, rainfall same as SCS input• Ponding adjustment applied outside TR-55

TR-55 AnalysisTR-55 Model Components

• SCS spreadsheet data entry• Open WinTR-55• Add/select dimensionless unit

hydrograph• Enter site information and

input values• Enter rainfall data• Run calculation


• SCS spreadsheet data entry

• Open WinTR-55• Add/select dimensionless unit

hydrograph• Enter site information and input

values• Enter rainfall data• Run calculation






• SCS spreadsheet data entry• Open WinTR-55• Add/select dimensionless

unit hydrograph• Enter site information and input












hydrograph• Enter site information and

input values• Enter rainfall data• Run calculation





















HEC-HMS Model• Software available free from USACE• Typical uses:

• Reservoir routing• Combine hydrographs• Hydrograph requests

• Flows from SCS method• Use SCS settings for RCN, precipitation• Use Clark Transform, adjust storage coefficient

Services• Hydrographs

• Matched to estimated peak• Typically constructed/estimated• Extrapolated from gage data where available

• Reservoir Routing• Typically requested for dams• Rating curve must be provided (elevation vs. volume/area vs. flow)

• Hydrology Review• FEMA mapping projects• Letters of Map Revision (LOMR)

Services• Guidance and Training

• Michigan-specific hydrologic methodologies• Appropriate method selection

• Mapping• GIS shapefile or PDF of watershed• GIS backup data if already created• CSS Open GIS Portal

Susan E. Greiner, P.E.Environmental Engineer

Hydrologic Studies and Dam Safety Unit | Water Resources DivisionDepartment of Environmental Quality

517.284.5579 [email protected]

Documents

Flood Hydrology - ctt.mtu.edu · • Statistical Analysis of USGS Gage Data (Gage) • Statistical Models for Estimating Flow Characteristics of Michigan Streams (Regression)