Water-Resources Investigations Report 97-4279

Technique for Simulating Peak-Flow Hydrographs in Maryland

By Jonathan J.A. Dillow


This report is available as a pdf.



The efficient design and management of many bridges, culverts, embankments, and flood-protection structures may require the estimation of time-of-inundation and (or) storage of floodwater relating to such structures. These estimates can be made on the basis of information derived from the peak-flow hydrograph. Average peak-flow hydrographs corresponding to a peak discharge of specific recurrence interval can be simulated for drainage basins having drainage areas less than 500 square miles in Maryland, using a direct technique of known accuracy. The technique uses dimensionless hydrographs in conjunction with estimates of basin lagtime and instantaneous peak flow.

Ordinary least-squares regression analysis was used to develop an equation for estimating basin lagtime in Maryland. Drainage area, main channel slope, forest cover, and impervious area were determined to be the significant explanatory variables necessary to estimate average basin lagtime at the 95-percent confidence interval. Qualitative variables included in the equation adequately correct for geographic bias across the State. The average standard error of prediction associated with the equation is approximated as plus or minus (+/-) 37.6 percent. Volume correction factors may be applied to the basin lagtime on the basis of a comparison between actual and estimated hydrograph volumes prior to hydrograph simulation.

Three dimensionless hydrographs were developed and tested using data collected during 278 significant rainfall-runoff events at 81 stream-gaging stations distributed throughout Maryland and Delaware. The data represent a range of drainage area sizes and basin conditions. The technique was verified by applying it to the simulation of 20 peak-flow events and comparing actual and simulated hydrograph widths at 50 and 75 percent of the observed peak-flow levels. The events chosen are considered extreme in that the average recurrence interval of the selected peak flows is 130 years. The average standard errors of prediction were +/- 61 and +/- 56 percent at the 50 and 75 percent of peak-flow hydrograph widths, respectively.






Purpose and Scope

Description of Study Area

Previous investigation


Description of data base

Methods of study

Streamgaging station selection

Hyetograph development

Predictor variable identification

Analytical methods

Determination of lagtime

Basin lagtime

Regional analysis

Testing of lagtime equation

Verification by prediction error sum of squares (PRESS)

Variable bias by residual plots

Sensitivity to variable errors

Development of dimensionless hydrographs

Regionalization of dimensionless hydrographs

Testing of dimensionless hydrographs

Shape verification

Geographical and width bias

Sensitivity to peak flow and lagtime

Hydrograph-width relations

Adjustment for correct runoff volume

Verification of the simulation technique

Limitations of technique

Hydrograph simulation technique

Simulating a peak-flow hydrograph

Estimating peak flow

Estimating lagtime

Expanding the dimensionless hydrograph

Summary and conclusions

Selected references

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For more information about USGS activities in Maryland, Delaware and the District of Columbia contact:


MD-DE-DC Water Science Center
U.S. Geological Survey
8987 Yellow Brick Road
Baltimore, MD 21237
Telephone: (410) 238-4200
Fax: (410) 238-4210


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Last modified: Thursday, September 01 2005, 02:25:15 PM
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