FLOOD10617 ‎(2)‎

• County: Boulder
• Community: Boulder County and Incorporated Areas
• Title: FIS - Boulder County and Incorporated Areas - Vol 1
• Date: 10/4/2002
• Prepared For: Boulder County
• Prepared By: FEMA
• Floodplain - Doc Type: Current FEMA Regulatory Floodplain Information

Starting water-surface elevations were dete~ned ~ the SCS
(Reference 35). Using stream slope at a starting valley section.
water-surface profiles for the 10-, 50-, 100-, and SOO-year floods
were developed using the SCS WSP2 and TR20 computer programs
(References 35 and 36, respectively).

Locations of selected cross sections used in the hydraulic analyses
are shown OD the Flood Profiles (Exhibit 1). For stream segments
for which a floodway was computed (Section 4.2), selected cross
section locations are also shown on the Flood Insurance Rate Map
(Exhibit 2).

The hydraulic analyses for this study were based on unobstructed
flow. The flood elevations shown on the profiles are thus
considered valid only if hydraulic structures remain unobstructed,
operate properly, and do not fail.

All elevations are referenced to the National Geodetic Vertical
Datwn of 1929 (NGVD) . Elevation reference marks and the
descriptions of the marks used in this study are shown on the maps.

4.0 FLOODPLAIN MANAGEMENT APPLICATIONS

The NFIP encourages State and local governments to adopt sound floodplain
management programs. Therefore, each Flood Insurance Study provides
lOO-year flood elevations and delineations of the 100- and SOO-year
floodplain boundaries and lOO-year floodway to assist communities in
developing floodplain management measures.

4.1 Floodplain Boundaries

To provide a national standard without regional discrimdnation, the
1 percent annual chance (lOO-year) flood has been adopted ~ FEMA
as the base flood for floodplain management purposes. The
0.2 percent annual chance (SOO-year) flood is employed to indicate
additional areas of flood risk in the community. For each stream
studied ~ detailed methods, the 100- and SOD-year floodplain
boundaries have been delineated using the flood elevations
determined at each cross section. Between cross sections, the
boundaries were interpolated using topographic maps at scales of
1:1,200, 1:2,400, 1:4,800, and 1:6,000, with contour intervals of
2, 4, 10, and 40 feet, respectively (References 47, 49. 54, 55, 56,
57, and 58).

Floodplain boundaries in other portions of Boulder County have been
revised to include boundary info~tion shown on topographic work
maps included with the reports referenced in Section 7.0.

The 100- and SOQ-year floodplain boundaries are shown OD the Flood
Insurance Rate Map. On this map, the 100-year floodplain boundary
corresponds to the bounda~ of the areas of special flood hazards
(Zones A, AE, AH, and AO); and the SOO-year floodplain boundary
corresponds to the boundary of areas of moderate flood hazards. Zn

47