U.S. Geological Survey
Water-Resources Investigations Report 99-4142
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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.
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 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
References
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
District Chief
U.S. Geological Survey
GSA Center, Suite 400-15
651 Federal Drive
Guaynabo, Puerto Rico 00965-5703
U.S. Geological Survey
Branch of Information Services
Box 25286, Federal Center
Denver, CO 80225-0286
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