FLOOD08164

• Designation Number: 309
• County: Weld
• Community: Erie
• Basin: South Platte
• Title: Flood Insurance Study - Erie, Colorado, Boulder and Weld Counties
• Date: 9/1/1990
• Designation Date: 1/1/1991
• Floodplain - Doc Type: Floodplain Report/Masterplan

2.4 Flood Protection Measures

No structures provide flood protection in the Town of Erie.

3.0 ENGINEERING METHODS

For the flooding sources studied in detail in the communi ty, 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
selected as having special significance for floodplain management and
for flood insurance rates. These events, commonly termed the 10-, SO-,
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 avera2e period between
floods of a specific magnitude, rare floods could occur at short
intervals or even within the same year. The risk of experiencing a rare
flood increases when periods greater than 1 year are considered. For
example, the risk of having a flood which equals or exceeds the 100-year
flood (l percent chance of annual exceedence) in any SO-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.

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.

The peak discharges for the 10-, SO-, 100-, and SOO-year floods for
Coal Creek used in this study were developed by the SCS in a report
entitled Flood Hazard Analvses. Coal Creek and Rock Creek. Boulder
and Weld Counties. Colorado (Reference I). The SCS used synthetic
rainfall-runoff procedures, as described in the SCS's National
En2ineerin2 Handbook (Reference 4), and the TR-20 computer program
for flood routing (Reference S) in order to establish the selected
discharges along the stream.

Peak discharge-drainage area relationships for Coal Creek are shown
in Table I.

Analyses were carried out to establish the peak elevation-frequency
relationships for each flooding source studied in detail.

3.2 Hydraulic Analyses

Analyses of the hydraulic characteristics of flooding
sources studied were carried out to provide estimates
elevations of floods of the selected recurrence intervals.

from
of

the
the

S