FLOOD10652 ‎(2)‎

• County: Chaffee
• Community: Chaffee County and Unincorporated Areas
• Title: FIS - Chaffee County and Unincorporated Areas
• Date: 3/4/1987
• Prepared For: Chaffee County
• Prepared By: FEMA
• Floodplain - Doc Type: Current FEMA Regulatory Floodplain Information

The hazard from these debris flows is difficult to predict because
it is difficult to classify debris flows in terms of recurrence
interval, since historical data on amounts and depths of flow are
nonexistent 1 and because debris flows commonly change channel location
on the fan between events or within a single event.

The debris-flow season coincides with the season of maximum rainfall,
July through October. Most of this rain falls during intense cloud-
burst storms. Typically, two or three debris flows occur in this
area each year; however, none were recorded between 1976 and 1980.

Damage from debris flows has been limited to the periodic closing
of State Highway 162. With increased pressure for development in
this locale, the potential for damage and loss of life will increase.

2.4 Flood Protection Measures

There are no existing flood-control structures on the South Arkansas
River, Pancha Creek, Chalk Creek, or Cottonwood Creek.

Chaffee County has adopted zoning regulations for the management
of flood hazard areas (Reference 4).

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-, SO-, 100-, or SOO-year period (recurrence interval) have been se-
lected as having special significance for flood plain management and for
flood insurance rates. These events, commonly termed the 10-, 50-, 100-,
and SOO-year floods, have a 10, 2, 1, and 0.2 percent chance, respectively,
of being equaled or exceeded during any year. Although the recurrence
interval represents the long-term average period between floods of a
specific magnitude, rare floods could occur at short interval~ or even
within the same year. The risk of experiencing a rare flood increases
when periods greater than 1 year are considered. Per example, the risk
of having a flood which equals or exceeds the IOO-year flood (I percent
chance of annual exceedence) in any 50-year period is approximately 40
percent (4 in 10), and, for any 90-year period, the risk increases to
approximately 60 percent (6 in 10). The analyses reported herein reflect
flooding potentials based on conditions existing in the community at the
time of completion of this study. Maps and flood elevations will be
amended periodically to reflect future changes.

6