WRIR 99-4142
U.S. Geological Survey

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Estimation of Magnitude and Frequency of Floods for Streams in Puerto Rico: New Empirical Models

By Orlando Ramos-Ginés

In cooperation with the
Commonwealth of Puerto Rico

ABSTRACT

Flood-peak discharges and frequencies are presented for 57 gaged sites in Puerto Rico for
recurrence intervals ranging from 2 to 500 years. The log-Pearson Type III distribution, the
methodology recommended by the United States Interagency Committee on Water Data, was used
to determine the magnitude and frequency of floods at the gaged sites having 10 to 43 years of
record. A technique is presented for estimating flood-peak discharges at recurrence intervals
ranging from 2 to 500 years for unregulated streams in Puerto Rico with contributing drainage
areas ranging from 0.83 to 208 square miles. Loglinear multiple regression analyses, using climatic
and basin characteristics and peak-discharge data from the 57 gaged sites, were used to construct
regression equations to transfer the magnitude and frequency information from gaged to ungaged sites. The equations have contributing drainage area, depth-to-rock, and mean annual rainfall as the basin and climatic characteristics in estimating flood peak discharges. Examples are given to show a step-by-step procedure in calculating a 100-year flood at a gaged site, an ungaged site, a site near a gaged location, and a site between two gaged sites.

TABLE OF CONTENTS

Abstract

Introduction

Acknowledgments

Purpose and Scope

Physiography and General Climatology

Magnitude and Frequency of Floods at Gaging Stations

Discharge Data Available

Flood Frequency Analysis

Regional Magnitude and Frequency of Floods at Ungaged Sites

Basin Characteristics

Development of Regional Regression Equation

Final Region and Equations

Accuracy of Estimating Equations

Comparison of Estimates Using Different Models

Estimation of Peak Discharges Using Regression Equations

Gaged Sites

Ungaged Sites

Sample Computations

Summary and Conclusions

References

The citation for this report, in USGS format, is as follows:

Ramos-Ginés, Orlando, 1999, Estimation of magnitude and frequency of floods for streams in Puerto Rico: new empirial models: U.S. Geological Survey Water-Resources Investigations Report 99-4142, 41 p.,