Publications—Scientific Investigations Report

Prepared in cooperation with the New York State Department of Transportation

Magnitude and Frequency of Floods in New York

By Richard Lumia, Douglas A. Freehafer, and Martyn J. Smith

U.S. Geological Survey Scientific Investigations Report 2006–5112

The body of the report is available in PDF Format (22,233 KB)

Support page to SIR2006-5112

Abstract

Techniques are presented for estimating the magnitude and frequency of flood discharges on rural, unregulated streams in New York, excluding Long Island. Peak-discharge-frequency data and basin characteristics from 388 streamflow-gaging stations in New York and adjacent states were used to develop multiple linear regression equations for flood discharges with recurrence intervals ranging from 1.25 to 500 years. A generalized least-squares (GLS) procedure was used to develop the regression equations. Separate sets of equations were developed for each of six hydrologic regions of New York; standard errors of prediction range from 14 to 43 percent. Statistically significant explanatory variables in the regression equations include drainage area, main-channel slope, percent basin storage, mean annual precipitation, percent forested area, a basin lag factor, a ratio of main-channel slope to basin slope, mean annual runoff, maximum snow depth, and percentage of basin above 1,200 feet. Drainage areas for the 388 sites used in the analyses ranged from 0.41 to 4,773 square miles.

Methods of computing flood discharges from the regression equations differ, depending on whether the estimate is for a gaged or ungaged basin, and whether the basin crosses hydrologic-region or state boundaries. Examples of computations are included. Discharge-frequency estimates for an additional 122 streamflow-gaging stations with significant regulation or urbanization (including Long Island) are also included as at-site estimates.

Basin characteristics, log-Pearson Type III statistics, and regression and weighted estimates of the discharge-frequency relations are tabulated for the streamflow-gaging stations used in the regression analyses. Sensitivity analyses showed that mean-annual precipitation, drainage area, mean annual runoff, and maximum snow depth are the variables to which computed discharges are most sensitive in the regression equations.

Included with the report is a DVD that provides computation procedures and geographic information system spatial datasets to compute basin characteristics used in the regional regression equations and flood-frequency estimates at a specified location on a stream.

Table of Contents

Abstract

Introduction

Purpose and Scope

Description of Study Area

Physiography

Geology

Climate

Magnitude and Frequency of Flood Discharges

Database

Annual Peak-Discharge Records

Magnitude and Frequency of Flood Discharges at Streamflow-Gaging Stations

Basin Characteristics

Regression Analysis

Regionalization of Flood-Frequency Estimates

Delineation of Hydrologic Regions

Regional Basin and Peak-Discharge Characteristics

Regional Regression Equations

Full-Regression Equations

Drainage-Area-Only Equations

Computation of Peak Discharge

Gaged Sites

Ungaged Sites

Sample Computations

Limitations, Accuracy, and Sensitivity of Regression Equations

Suggestions for Further Study

Skewness Coefficient

Soil Maps

Small-Stream Data

Other Factors

Summary

Acknowledgments

Selected References

Appendix 1

New York Flood-Frequency Tool

System Requirements

Data Requirements

Installation of the New York Flood-Frequency Tool

Using the New York Flood-Frequency Tool

Limitations

Using the New York Flood-Frequency Spreadsheet

Future Updates

DVD

[in pocket]

Figures

1–2 Maps showing:

1. Physiographic provinces of New York, excluding Long Island

2. Six hydrologic regions of New York and locations of 388 streamflow-gaging stations represented in this study

3–6 Graphs showing:

3. Annual peak discharges and 100-year peak discharges for 388 rural, unregulated streamflow-gaging stations used in this study

4. Annual peak discharges and trend line for streams in two highly developed areas (A,B) and in an undeveloped area (C) in New York: (A) 01311000 – Pines Brook at Malverne, (B) 01302000 – Bronx River at Bronxville, and (C) 01512500 – Chenango River near Chenango Forks

5. Annual peak discharges and trend lines for (A) all study sites and (B) all small stream (10- to 50-square miles) study sites

6. Examples of flood-frequency curves for selected streamflow-gaging stations along the Hudson River in New York

7. Locations of 122 streamflow-gaging stations on regulated and urbanized streams in New York

8–9 Graphs showing:

8. Annual peak discharges and moving 100- and 2-year flood discharges for two streamflow-gaging stations in New York: (A) 01512500 – Chenango River near Chenango Forks, and (B) 04256000 – Independence River at Donnattsburg

9. Slopes of the lower half and upper half of the main channel for 388 streamflow-gaging stations used in the study

10–14 Maps showing:

10. Areas in and adjacent to New York with elevations above 1,200 feet, as interpreted from 30-meter digital elevation model (DEM) data

11. Areas of urbanization, forest, and storage in and adjacent to New York, as interpreted from the National Land Cover Dataset (NLCD) land-use data

12. Mean annual runoff in areas in and adjacent to New York

13. Mean annual precipitation in areas in and adjacent to New York

14. Seasonal maximum snow depth (50th percentile) in areas in and adjacent to New York

15–21 Graphs showing:

15. Boxplots of 50-year peak-discharge residuals from the statewide regression for streamflow-gaging stations within six hydrologic regions of New York, before and after regionalization

16. Boxplots of selected basin characteristics for streamflow-gaging stations within six hydrologic regions of New York

17. Boxplots of selected peak-discharge characteristics for streamflow-gaging stations within six hydrologic regions of New York

18. Distribution of streamflow-gaging stations within each of six hydrologic regions of New York and for all stations combined by (A) length of record, and (B) drainage-basin size

19. Monthly frequency of annual peak flows within each of six hydrologic regions of New York and for all streamflow-gaging stations combined for (A) all 388 study basins, and (B) 79 streams in small (less than 10-square miles) basins

20. Average flood-frequency curves for six hydrologic regions of New York and for all 388 study sites combined

21. Maximum, minimum, and average flood-frequency curves for six hydrologic regions of New York and for all 388 study sites combined

Tables

1. Full-regression equations for estimating peak discharges for rural, unregulated streams in each of six hydrologic regions of New York, excluding Long Island

2. Standard errors of prediction and equivalent years of record for full regression equations and drainage-area-only regression equations, for six hydrologic regions
of New York, excluding Long Island

3. Regression equations based on drainage area only for estimating peak discharges for rural, unregulated streams in each of six hydrologic regions of New York, excluding Long Island

4. Minimum, maximum, and median values for basin characteristics used in the regression analyses for six hydrologic regions in New York, excluding Long Island

5. Results of sensitivity analysis-percent change in computed 50-year peak discharges as a result of ±30-percent change in selected variables within each of six hydrologic regionsof New York, excluding Long Island

6. Selected statistics for skew coefficients for each of six hydrologic regions of New York, excluding Long Island

7. Location, drainage area, period of record, and maximum known discharge and recurrence interval for rural, unregulated streams in New York, excluding Long Island

8. Peak discharge for 10 selected recurrence intervals on rural, unregulated streams in New York, excluding Long Island

9. Location, drainage area, period of record, and calculated peak discharge for 10 recurrence intervals for regulated streams, and streams in urbanized basins in
New York, including Long Island

10. Data on selected basin characteristics of rural, unregulated streams in New York, excluding Long Island


Suggested Citation:

Lumia, Richard, Freehafer, D.A., and Smith, M.J., 2006, Magnitude and Frequency of Floods in New York: U.S. Geological Survey Scientific Investigations Report 2006–5112, 152 p.


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For further information, contact:

Director
U.S. Geological Survey
New York Water Science Center
425 Jordan Road
Troy, NY 12180

dc_ny@usgs.gov

(518)285-5600

or visit our Web site at: http://ny.water.usgs.gov

U.S. Department of the Interior, U.S. Geological Survey
Persistent URL: http://pubs.water.usgs.gov/sir20065112
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