FLOOD10780 ‎(3)‎

• County: Delta
• Community: Delta County and Unincorporated Areas
• Title: FIS - Delta County and Unincorporated Areas
• Date: 3/15/1984
• Prepared For: Delta County
• Prepared By: FEMA
• Floodplain - Doc Type: Current FEMA Regulatory Floodplain Information

Federal Emergency Management Agency as the base flood for
purposes of floodplain management measures. The 500-year flood
is employed to indicate additional areas of flood risk in the
county. For each stream studied by detailed methods, the
boundaries of the 100- and 500-year floods 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: 2 ,400 and 1 :4,800, with contour
intervals of 4, 2, and S feet (References 16, 18, and 19).

Approximate flood boundaries in some portions of the study area
were taken from the previously printed Flood Hazard Boundary Map
for Delta County (Reference 20).

Approximate flood boundaries for Minnesota Creek and Cedar Run
were determined using field observations and topographic maps at
a scale of 1:24,000, with a contour interval of 20 feet (Refer-
ence 21).

The approximate floodplain of Cedar Run is less than 200 feet in
width and is an area of minimal flooding. In accordance with the
Federal Emergency Management Agency guidelines, this approximate
area of minimal flooding is not shown in this study.

Flood boundaries for the 100- and SOO-year floods are shown on
the Flood Boundary and Floodway Map (Exhibit 2). In cases where
the lOO-and SOO-year flood boundaries are close together, only
the lOa-year flood boundary has been shown. Small areas within
the flood boundaries may lie above the flood elevations and,
therefore, not be subject to flooding; owing to limitations of
the map scale, such areas are not shown.

4.2 Floodways

Encroachment on floodplains, such as artificial fill, reduces the
flood-carrying capacity, increases the flood heights of streams,
and increases flood hazards in areas beyond the encroachment
itself. One aspect of floodplain management involves balancing
the economic gain from floodplain development against the
resulting increase in flood hazard. For purposes of the National
Flood Insurance Program, the concept of a floodway is used as a
tool to assist local communities in this aspect of floodplain
management. Under this concept, the area of the lOO-year flood
is divided into a floodway and a floodway fringe. The floodway
is the channel of a stream plus any adjacent floodplain areas
that must be kept free of encroachment in order that the lOO-year
flood may be carried without substantial increases in flood
heights. Minimum standards of the Federal Emergency Management
Agency limit such increases in flood heights to 1.0 foot,
provided that hazardous velocities are not produced. The
floodways in this report are presented to local agencies as
minimum standards that can be adopted or that can be used as a
basis for additional studies.

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