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I I I I I I I I I I I I I I I I I I I :1 1623.001 Report Summary #2 "Storm Drainage Requirements Proposed Facilities" by J. T.. Banner & Associates, Inc. Report Prepared in 1967 The purpose of this study was to estimate quantities of storm water runoff and propose storm drainage facilities including storm drains, channel improvements and detention ponds. The report covers in depth the storm sewer system existing at that time, but none of this information will be included here since it also appears in later reports. The Rational method was used in this report to estimate storm runoffs. Rainfall intensity-duration curves for Fort Collins for duration periods up to four hours and for 2-year, 5-year, 10-year, 25-year, 50-year and 100-year storm frequencies were used as shown on Page 2-2. Data for these curves was obtained from U. S. Weather Bureau Technical Paper #28. Storm frequencies used for design are shown on Page 2-3 along with runoff coefficients. A composite runoff factor "C" of 0,25 for the area ~!est of the Larimer County #2 Canal and the undeveloped drainage area of Spring Creek was used in this study, For the same area under complete development, a "C" value equal to 0.50 was assumed. Developed areas in the city had "C" values ranging from 0.42 to 0.55 for each block. For the design of storm water facilities, the four irrigation canals were assumed to divert from Spring Creek water that normally flows into them from the west, therefore reducing the size and cost of facilities downstream. Detention ponds were recommended for flood protection, This report included several pages of photographs that are included along with rainfall-duration curves, runoff and a summary of structures along Spring Creek as they existed in 1967. The information contained in this report is out of date and should not be used since advances have been made in flood plain analysis and more recent rainfall data is available.