FLOOD06078

• Designation Number: 545
• County: La Plata
• Community: Durango
• Basin: San Juan/Dolores
• Title: FIS - Durango La Plata County
• Date: 5/21/2001
• Designation Date: 5/21/2001
• Floodplain - Doc Type: Floodplain Report/Masterplan

approximately 0,39 mile upstream of La Posta Road and from
approximately 0.58 mile upstream of 32nd Street to -approximately
3.56 miles upstream of 32nd Street, along Dry Gulch Creek from
approximately 1,500 feet upstream of the confluence with Junction
Creek to approximately 5,670 feet upstream of Borrego Drive, and
along Lightner Creek from the confluence with the Animas River to
approximately 1,800 feet upstream of the confluence with the
Animas River.

The hydraulic analyses for this restudy were performed by
Foothill Engineering Consultants, Inc" for FEMA, under Contract
No, EMW-93-C-4150, This work was completed in May 1998,

The floodway determination and boundary delineations for Lightner
Creek and the upper portion of the Animas Ri ver from
approximately 0.58 mile upstream of 32nd Street to approximately
3,56 miles upstream of 32nd Street were completed by Michael
Baker Jr., Inc'f for FEMA, in February 1999.

The peak diSCharge-frequency relationships for the
streams were taken from previous Flood Insurance Studies
City of Durango, Colorado (Reference 10), and La Plata
Colorado (Reference 11),

studied
for the
County,

Water-surface elevations for the 10-, 50-f 100-, and SOa-year
flood events were computed using the BOSS River Modeling System
(RMS) (Reference 12), BOSS RMS is an Autocad-based program
designed to simplify the input processing of the U.S. Army Corps
of Engineers HEC-2 computer program (Reference 13).

Topographic maps with 2-foot contour intervals were acquired from
the City of Durango, in the form of Autocad drawing files. These
maps were created from aerial photography flown April 4, 1994.
Bridge inspection and construction drawings were available for
the bridges over the Animas River. These drawings were used as
input data for the HEC-2 models. A limited number of surveyed
cross sections of the Animas River were provided by the City of
Durango. These sections were used to supplement the Autocad map
and bridge data.

Field investigations were conducted to visually confirm the
topographic mapping, verify culvert and bridge geometry, a~d
estimate roughness coefficients (Manning's \'n" values) for the
studied streams. Roughness coefficients for the main ''=:!--ictrmel
depended on channel condition and obstructions. Rougn~ess
coefficients for the floodplain depended on vege':""T: i,oP..,
irregularitYf obstructions, and meandering (Reference 14). The
ranges of Manning's "n" values used for each stream are shown in
Table 3, "Manning's "n" Values."

The starting water-surface elevations were calculated using
normal depth or critical depth as appropriate.

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