Water-Resources Investigations Report 97-4118

COMPARISON OF THE 2-, 25-, AND 100-YEAR RECURRENCE INTERVAL FLOODS COMPUTED FROM OBSERVED DATA WITH THE 1995 URBAN FLOOD-FREQUENCY ESTIMATING EQUATIONS FOR GEORGIA

This report is available online in pdf format (1 MB): USGS WRIR97-4118 (Opens the PDF file in a new window. )

Ernest J. Inman

U.S. Geological Survey Water-Resources Investigations Report 97-4118, 14 pages (Published 1997)

ABSTRACT

Flood-frequency relations were computed for 28 urban stations, for 2-, 25-, and 100-year recurrence interval floods and the computations were compared to corresponding recurrence interval floods computed from the estimating equations from a 1995 investigation. Two stations were excluded from further comparisons or analyses because neither station had a significant flood during the period of observed record.

The comparisons, based on the student's t-test statistics at the 0.05 level of significance, indicate that the mean residuals of the 25- and 100-year floods were negatively biased by 26.2 percent and 31.6 percent, respectively, at the 26 stations. However, the mean residuals of the 2-year floods were 2.5 percent lower than the mean of the 2-year floods computed from the equations, and were not significantly biased. The reason for this negative bias is that the period of observed record at the 26 stations was a relatively dry period. At 25 of the 26 stations, the two highest simulated peaks used to develop the estimating equations occurred many years before the observed record began. However, no attempt was made to adjust the estimating equations because higher peaks could occur after the period of observed record and an adjustment to the equations would cause an underestimation of design floods.


CONTENTS

Abstract

Introduction

Background

Purpose and Scope

Flood-frequency analyses

Statistical methods used for flood-frequency comparisons

Comparison of flood-frequency data

Results of comparisons

Summary

References cited

 


REPORT AVAILABILITY

This report is available online in pdf format (1 MB): USGS WRIR97-4118 (Opens the PDF file in a new window. )
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