FLOOD00918

• County: Larimer
• Community: Fort Collins
• Title: Precipitaion Frequency Study
• Date: 7/16/1998
• Prepared For: Fort Collins
• Prepared By: WRC Engineering, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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NOAA will be embarking on study that will be intended to replace NOAA Atlas 2. This scope, project
area boundaries and funding for this study is currently being negotiated with several state agencies.
NOAA could begin work on this study in 1999. However, completion of the study may take several
years. Therefore, there is a need to adopt revised rainfall data before the NOAA study is initiated.
This recommended values in this report are based on similar statistical procedures to those that will be
used by NOAA. with exception to the use of "at-site" rather than regional analysis results. Therefore,
the recommended values shown in Table 5 may be higher than the values that will be reported by
NOAA.

The modification of the rainfall depth-duration-frequency statistics will also required a revision to the

temporal distribution that is also recommended by the City of Fort Collins. The revised time

distribution is not included in this report.

IV. QUALITATIVE STUDY

A.

DATA COLLECTION:
The data used in this study was obtained courtesy ofMr. James F. Wirshbom, Director of Mountain States
Weather Services. The data included weather watcher reports for twenty-eight major storm events from
June 1983 to August 1997. A list of said events is included in Table-6. The weather watcher stations
included in said analysis are included in Table-7 and shown on Figure-9. The rainfall data from all
weather watcher stations in the Fort Collins area was input into a computer spreadsheet for analysis. This
included data ranging from stations for which only one record existed for the storms in the study period
to stations for which records existed for all twenty-eight storms events. A printout of this data set is
included in Appendix G

B.

DATA ANALYSIS:
Several methods of analysis were used to analyze the data. First, the data was sorted and analyzed by
dividing the stations into two different regions: Region I included all stations west of the center of the
City of Fort Collins and Region 2 included all stations east of the center of the City (See Figure 9). In
general terms, the center of the City for this study was established as a north-south line extending through
the weather station on the Colorado State University Campus. This method of sorting was used after
reviewing preliminary data sorts considering three areas (east, middle, west) which showed no

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