WWRC 83-08
Design Rainfall Distributions for the State of Wyoming
Introduction
The design of hydraulic structures for use in ungaged drainage basins
requires some estimate of flood flows and their frequency of occurrence.
Because no historical streamflow data exist for these drainages, floods are
estimated either by regional frequency analysis or, with the help of
digital computers, by parametric rainfall-runoff event simulation.
Computer models dealing with rainfall-runoff event simulation are
commonly used today by engineers and hydrologists. These models are used
to predict flood hydrographs given an input rainfall volume, distributed
over time in some manner, and certain geomorphic basin parameters.
Studies exist in the literature documenting the effects of time
distribution of rainfall on runoff hydrographs. The reader is referred to
works by Wei and Larson (1971), Yen and Chow (1980), and Shanholtz and
Dickerson (1964) as examples. Because this relationship between the time
distribution of rainfall and hydrograph characteristics exists, the separate
study of storm rainfall is essential for accurate flood prediction
regardless of other variables that also influence the runoff process.
Additionally, methods of constructing design storms are available and in
wide use, but they are general in nature and assume storms occur with the
same temporal distribution across much of the country. Because of the
drastic climatic differences between the areas encompassed by existing
procedures, it was felt their design curves are not likely to be
representative of the actual time distribution of storms in semi-arid
regions such as Wyoming. It was, therefore, decided to develop a new
design storm construction procedure applicable to the State of Wyoming
based on observed storm rainfall in Wyoming. This new design storm
methodology is the topic addressed herein.
83-08 Table of Contents
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