Short-Duration Rainfall Intensity Equations for Urban Drainage Design

Abstract

A practical method for developing rainfall-intensity equations for short durations (approximately one hour or less) for locations in the United States covered by NOAA Atlas 14 Volumes 1, 2, 3, and 4 is presented. For the semiarid western United States covered by Volume 1, for Puerto Rico and the U.S. Virgin Islands covered by Volume 3, and for Hawaii covered by Volume 4, single formulas apply to rainfall of all average recurrence intervals (ARIs). For the central and mid-Atlantic regions of the United States covered by Volume 2, formula coefficients are provided for several ARIs ranging from 1.58 to 1,000 years. All equations are based on a single-term exponential expression plus a constant that provides excellent fits to the available data. Mathematical expressions for the central and mid-Atlantic region coefficients as functions of the ARI are provided to simplify application of the approach. Mathematical relations representing design storm hyetographs are developed using the intensity-duration expression by distributing rainfall about the time of peak intensity proportioned by a factor