Water-Resources Investigations Report 95-4154

Technique for Estimating Magnitude and Frequency of Peak Flows in Maryland

By Jonathan J. A. Dillow


This report is available as a pdf.


Errata for equations 18 Dec 1997



A convenient and reliable technique for estimating flood magnitudes is required for effective flood-plain management and for the efficient design of bridges, culverts, embankments, and flood-protection structures. Methods are presented for estimating peak-flow magnitudes of selected frequencies, ranging from 2 to 500 years, for all nontidal drainage basins in Maryland. The methods were developed by generalized least-squares regression techniques using data from 219 gaged basins in and near Maryland.

The State is divided into five hydrologic regions: the Appalachian Plateaus and Allegheny Ridges region, the Blue Ridge and Great Valley region, the Piedmont region, the Western Coastal Plain region, and the Eastern Coastal Plain region. These regions correspond to the physiographic provinces of the State, with the exceptions that (1) the Coastal Plain Province is divided into two hydrologic regions, and (2) there is no distinct hydrologic region corresponding to the Valley and Ridge Province as it is divided into its constituent Allegheny Ridges and Great Valley subdivisions. Sets of equations for calculating peak discharges based on physical basin characteristics are provided for each of the regions.

Based on the peak-flow equations, methods for estimating peak flows are presented for ungaged and gaged streams in Maryland. The methods and equations are supported by generalized least-squares analysis of basin and flood-frequency characteristics data from 219 drainage basins in and near Maryland.

estimates for each of the five regions are calculated using combinations of the fol-lowing basin characteristics: drainage area, forest cover, basin relief, carbonate rock coverage, storage, and runoff-curve number. Drainage area contributes to the estimate in all five study regions. Carbonate rock coverage is used only in the Blue Ridge and Great Valley region. Storage and runoff-curve number are used solely in the Eastern Coastal Plain region. All other basin characteristics are used in two or more regions. Standard errors of estimate for the regression equations range from 19 to 31 percent in the Appalachian Plateaus and Allegheny Ridges region, 34 to 47 percent in the Blue Ridge and Great Valley region, 33 to 48 percent in the Piedmont region, 45 to 64 percent in the Western Coastal Plain region, and 36 to 42 percent in the Eastern Coastal Plain region.






Purpose and scope

Description of study area

Physiographic setting

Geologic setting


Data collection and analysis

Criteria for station selection

Station flood-frequency analysis

Explanatory variable identification

Methods for estimating magnitude and frequency of floods

Magnitude estimation method for ungaged streams

Demonstration of the estimation method for ungaged streams

Sensitivity analysis of explanatory variables

Accuracy and limitations

Magnitude estimation method for gaged streams

Estimation method for a site at a gaged location

Estimation method for a site near a gaged location

Estimation method for a site between gaged locations

Summary and conclusions

Selected references



Analysis of the streamflow-gaging-station network

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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, 03:32:33 PM
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