FLOOD10329

• Designation Number: 581
• County: Hinsdale
• Community: Hinsdale County
• Stream Name: Los Pinos, Weminuche, Middle Fork Piedra, E. Fork
• Title: Floodplain Information Report, Hinsdale County, Colorado
• Date: 9/1/2004
• Prepared For: Hinsdale County and CWCB
• Prepared By: Love and Associates, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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ENGINEERING METHODS

Hvdrolol!ic Analvsis

Flood peaks for the 10-, 50.., 100, and 500-year events for Henson Creek and Lake Fork
were analyzed comparing three statistical methods. The selected statistical method was
based on regional area analysis. For the FIR, it is assumed these flood peak estimates are
accurate, however, it should be noted the estimates are generally higher than those
obtained using more recent publications using regression based methods (CWCB, 1999,
and Vaill, 2000). In addition, drainage areas for Lake Fork used for the flood estimates
were slightly higher than those estimated for the current study, however, the change in
the magnitude of the 100-year flood peak is insignificant when the smaller drainage areas
are applied to the regression curve used in the original study. These flood peaks are
summarized in Table 1.

Table 1. Flood Peak Discharge Summary

Location/Design Flood Peak Dischar~e (cfs)
Point (DP) 10-year 50-year 100-year 500-year
Henson Creek
At Lake City 1400 2000 2300 3300
(H1)
Lake Fork Gunnison River
County Line (L 1 ) 6400*
Lake City Below 3000 4800 5800 9500
Henson Creek
(L2)
Lake City Above 2000 3100 3600 5600
Henson Creek
(L3)

See Catchment Area Map for Design Points
* 100-year discharge obtained from the area/discharge regional discharge curve used for
the FIS (WestWater, 1985a); drainage area at Design Point L1 equals 269 sq. mi.

The FIRM identifies approximate floodplains for portions of Lake Fork, Henson Creek,
Cebolla Creek, Mineral Creek, Spring Creek, North Clear Creek, South Clear Creek, Rito
Hondo Creek, Big Spring Creek, Crooked Creek, Rio Grande River, Little Squaw Creek,
Squaw Creek, Weminuche Creek, Los Pinos River, Middle Fork Piedra River, East Fork
Piedra River, Piedra River, Williams Creek, and Weminuche River, a few unnamed
tributaries, and numerous reservoirs and lakes. Flood peaks discharges for the 100-year
were estimated for some of these streams at important design points using regression
equations developed by CWCB (CWCB, 1999).

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