FLOOD10333

• County: Eagle
• Community: Vail
• Stream Name: Gore Creek and Tributaries
• Title: Hydrology Report, Gore Creek and Tributaries
• Date: 4/5/1999
• Prepared For: Vail
• Prepared By: J.F. Sato and Associates
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Background Information

The current flood hazard information for the town of Vail is based on hydrologic studies that
were completed more than 20 years ago. The town of Vail has annexed additional area to its
corporate limits since previous flood studies were made and those reaches need to be included in
the current investigations. There are also a few differences between two previous hydraulic
studies that have been identified for some reaches including a variation in stationing and
hydraulic computations for flow through bridge openings. The community has provided new
cross section data that will be used in developing new water surface profiles. Given these
considerations, it was determined that the flood discharge potential on these streams should be
restudied and the results included in new floodplain delineation's.

The hydrologic investigations for this study includes review of previous studies and new
statistical evaluations of peak flow data for 20 individual USGS streamgages in the Gore Creek
basin and streamgages for other basins in the eastern Eagle County region that have similar
hydrologic characteristics. Results of analysis of individual streamgages in the basin were
adopted for the reaches for which they were applicable. New peak flow regression equations
were developed using the results of the statistical analysis of individual station records and by
relating them to their drainage areas. These regression equations were then used to develop 10-,
50-, 100-, and 500-year discharge frequency values for study reaches without individual
streamflow gages.

II. PREVIOUS HYDROLOGIC STUDIES

Hydro-Triad, L TD, Lakewood, Colorado

This firm prepared a Gore Creek Floodplain Information Report (dated June, 1975) for the
Colorado Water Conservation Board. The purpose of the floodplain report was to define
flooding threats to existing developments from streams in the vicinity of Vail and to provide
information for guiding orderly growth within the valley. The report included: a discussion of
the Gore Creek area history and background; Gore Creek basin description; hydrology based on
data then available; channel flow characteristics and flooding; and discussion about Black Lake
Dams. The hydrologic section included information on hydrologic records, moisture sources,
rainfall precipitation, snowfall precipitation and snowpack, streamflow, and effects of
development on discharges. This was a quality detailed floodplain study that provided
significant information and reflected the state-of-practice at the time the studies were made.

Hydro- Triad, L TD analyzed eight streamflow gages in the Gore Creek valley that had periods of
record ranging from 8 to 20 years in length. In addition, they analyzed streamflow records for
six stations outside the Gore Creek Basin that had similar orientation and orographic
characteristics. Each of these gages were statistically analyzed using a Log-Normal relationship
as well as a Log-Pearson III for comparative purposes. The values derived from the 14 Log-
Normal snowmelt discharge probability analyses were used in developing snowmelt discharge
curves versus area for 2-, 10- 25-, 50-,and 100-year events. A 500-year event was established by

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