34 SEWER DESIGN 



once in several years as was thought to be the case; also, that 

 rains of a much heavier rate occur, lasting from ten to forty 

 minutes. For example, in 1890 there were reported in New 

 York State eleven storms contributing over an inch in an hour, 

 and in Massachusetts six.* 



In the spring of 1889 five self-registering rain-gages were 

 stationed throughout the country. This number has since 

 been increased to over two hundred, and there are now published 

 in the Monthly Weather Review tables of maximum rainfall in 

 five-, ten-, and sixty-minute intervals, giving valuable data 

 for all parts of the country. 



The special bulletin " D " of the Weather Bureau for 1897 

 deals largely with this question of excessive rains. This bulletin, 

 issued in direct response to the request of a number of civil and 

 municipal engineers, gives the maximum intensities at Weather 

 Bureau stations equipped with self -registering rain-gages. 

 Its accompanying text is, in part, as follows : 



" Excessive rains of high intensity are not prevalent on the 

 Western coast, although there the total annual rainfall is greater 

 than in any other portion of the United States. In the Western 

 States are found the most violent rains of this class, that is, 

 the cloudbursts of the mountainous and arid regions. The 

 rain seems to pour down rather than to fall in drops. The 

 amount of water falling has never been ascertained. In August, 

 1890, a storm passed over Palmetto, Nev., and contributed to 

 a rain-gage, not exposed to the full intensity of the storm, 

 8.8 inches in an hour. In August, 1891, two storms passed 

 Campo, Col., within a few moments of each other, and the 

 gage, before being carried away by the storm, showed a fall 

 of 11.5 inches during the hour. But these downpours are 

 found only between the Sierras and the foothills of the Rockies; 

 while the common heavy rainfalls are found east of the io5th 

 meridian, and principally during the summer months. They 

 are most frequent in connection with summer-afternoon thunder- 

 storms, but occasionally occur in the track of the West Indian 



* Weather Review for 1890. 



