United States Department of Transportation
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Abstract:Recently developed improved methods for highway storm water drainage require information on the temporal distribution of rainfall (i.e., hyetograph) in addition to the average rain intensity. The triangular design hyetograph method is developed as a practical method to provide the local storm hyetograph for design of small highway drainage facilities. The method is based on the methods of moments, using and preserving the statistical mean of the first time moment of rainstorms. The method is proposed as a trade-off between theoretical sophistication and practical simplicity. A total of 293,946 rainstorms from the hourly precipitation data of 222 National Weather Service stations and 5 to 60 minute data of 13 raingage stations of USDA Agricultural Research Service were analyzed to provide the statistical values of the hyetograph parameters for the United States. In Volume II existing methods to describe the temporal distribution of the rainfall of a design storm are first briefly reviewed. Next, different definitions of rainstorms are discussed. The theory of the first-moment triangular design hyetograph method is presented. Details of the rainstorm data utilized are described. The results of the statistical analysis of the data are summarized and discussed. From these results a national map of the value of the nondimensional peak rain time of the triangular hyetograph is developed for use in highway storm drainage designs.
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