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

U.S. Geological Survey
Water-Resources Investigations Report 99-4142


by Orlando Ramos-Ginés


The full report is available in pdf. Links to the pdf.


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




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 equations

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


Appendix 1. Comparison of log-Pearson Type III (Bulletin 17B weighted) estimates and estimates using empirical models

Appendix 2. FORTRAN program to calcute the 2-, 5-, 10-, 25-, 50-, 100-, and 500-year peak flows for ungaged, unregulated rural streams in Puerto Rico based on new regression equations presented in this report

For more information contact:

District Chief

U.S. Geological Survey

GSA Center, Suite 400-15

651 Federal Drive

Guaynabo, Puerto Rico 00965-5703



Copies of this report can be purchased from:

U.S. Geological Survey

Branch of Information Services

Box 25286, Federal Center

Denver, CO 80225-0286


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