FLOOD02981

• County: Ouray
• Community: Ouray County and Unincorporated Areas
• Basin: Gunnison
• Title: FIS - Otero County Unincorporated Areas
• Date: 7/3/1985
• Prepared For: Ouray County and Unincorporated Areas
• Prepared By: FEMA
• Floodplain - Doc Type: Current FEMA Regulatory Floodplain Information

Minor gravel operations exist near the Uncompahgre River channel
at Ridgway.

2.3 Principal Flood Problems

Floodflows on the Uncompahgre River within the study area result
from the rapid melting of the mountain snowpack during the period
of May through early July. This snowmelt is occasionally augmented
by rainfall. The runoff from snowmelt typically sustains periods
of high flows and marked daily fluctuation.

All streams that tributary to the Uncompahgre River within the study
area drain minor areas and, while many are subject to cloudburst-
type flooding, none drain areas large enough to individually affect
the peak flows in the main channel of the Uncompahgre River.

The earliest reference to flooding on the Uncompahgre River is
contained in USGS Water-Supply Paper 997 (Reference 3). Widespread
flooding occurred during the spring and early summer of 1884 due
to melting snowpack.

USGS gaging stations along the Uncompahgre River show that, during
the period of record (intermittently from 1903 to the present),
the highest peak flow occurred in 1921 (Reference 4). The flow
reached a volume of 2,000 cubic feet per second (cfs) at OUray,
2,400 cfs below OUray, and 4,080 cfs at Colona. Other major high
flows occurred in August 1909, July 1927, July 1929, July 1965,
and July 1973. Major damage during these events occurred in and
near the City of Ouray. Examples of flood damage are shown in
Figures 2 through 5.

2.4 Flood Protection Measures

In the wider valley where the Uncompahgre River West Arm exists,
an attempt has been made to confine flows to the present newer
channel by the grading of berms with native alluvial material.
These berms provide adequate protection during normal flowSI how-
ever, because the berms are constructed on permeable material,
they offer little flood protection during higher flow.

3.0 ENGINEERING METHODS

For the flooding sources studied in detail in the community, standard
hydrologic and hydraulic study methods were used to determine the flood
hazard data required for this study. Flood events of a magnitude which
are expected to be equaled or exceeded once on the average during any
10-, 50-, 100-, or 500-year period (recurrence interval) have been
selected as having special significance for flood plain management and
for flood insurance rates. These events, commonly termed the 10-, 50-,
100-, and 500-year floods, have a 10, 2, 1, and 0.2 percent chance,

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