FLOOD08741

• Designation Number: 322
• County: La Plata
• Community: Durango
• Basin: San Juan/Dolores
• Title: Flood Insurance Study - Durango, Colorado
• Date: 12/1/1989
• Designation Date: 7/1/1992
• Floodplain - Doc Type: Floodplain Report/Masterplan

3.1 Hydrologic Analyses

Hydrologic analyses were carried out to establish peak discharge-
frequency relationships for each flooding source studied in detail
affecting the community.

Methods
include
method.
Pearson

employed in the COE's frequency analyses (Reference 3)
streamflow records analysis and the synthetic hydrograph
Peak discharge values were obtained by the COE from a log-
Type III distribution (Reference 4).

Frequency analyses for the Animas River were based on streamflow
records of rain and snowmelt flood and on data from historic floods.
Eleven stream-gage records, having an average length of
appro~imately 30 years, were used; the longest record was 57 years.

Frequency analyses for Junction Creek were based on streamflow
records and on data developed from similar stream basins in the
region. Frequency analyses for Dry Gulch Creek were based on the
synthetic hydrograph method because historic floodflow and
precipitation data were not available.

Peak discharge-drainage area relationships for the Animas River,
Junction Creek, and Dry Gulch Creek are shown in Table 1.

Table 1. Summary of Discharges

Flooding Source
and Location

Drainage Area
(square miles)

Peak Discharges (cfs)
10-Year 50-Year 100-Year 500-Year

Animas River
At Northern
Corporate Limits
At Confluence With
Junction Creek
At Confluence With
Lightner Creek

649

9,800

17 , 500

22,500

38,000

690

10,000

18,000

23,000

39,000

760

10,200

18,500

23,500

40,000

Junction Creek
At Mouth

39

1,500

3,000

4,350

7,700

Dry Gulch Creek
At Mouth

4

150

650

1,200

3,000

3.2 Hydraulic Analyses

Analyses
community
floods of

of the hydraulic characteristics
were carried out to provide estimates
the selected recurrence intervals.

of streams in the
of the elevations of

7