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<br />'physiographic effects in the subbasin. The subbasin-mean recording <br /> <br /> <br />precipitation pattern (time distribution) is computed in a similar <br /> <br /> <br />manner with station weights as appropriate. The subbasin-mean precipita- <br /> <br /> <br />tion distribution (time distribution of total storm rainfall) is then <br /> <br /> <br />computed using the relative pattern to distribute the total subbasin <br /> <br /> <br />rainfall. <br /> <br />b. Known temporal and spatial precipitation for a subbasin can <br />be supplied directly. By this method precipitation can be supplied <br />for each interval or as a time pattern for a given storm total. Precipita- <br /> <br />tion distributions may also be specified for two differently sized areas and <br /> <br />the program will perform a logarithmic interpolation of the two patterns <br /> <br />for a specified area. <br />c. The program provides for automatic computation of standard <br /> <br />project storm (SPS) precipitation using Corps of Engineers criteria and <br />for probable maximum precipitation using criteria developed by the National <br />Weather Service. For the SPS, the largest day of precipitation is preceded <br />by the second largest and followed by the third largest, Six-hour storm <br />amounts within each day are similarly distributed. A storm transposition <br />coefficient can be supplied or will be computed by the program as a default <br />option. <br />Where snowfall and snowmelt are considered, there is provision for <br /> <br />separate computation in up to ten elevation zones. These zones are usually <br /> <br />considered to be in elevation increments of 1,000 feet, but any equal <br />increments of elevation can be used as long as the air temperature lapse <br /> <br />9 <br />