FLOOD05659

• County: Statewide
• Basin: Statewide
• Title: Alluvial Fans: Hazards and Management
• Date: 2/1/1989
• Prepared For: US
• Prepared By: FEMA
• Floodplain - Doc Type: Historic FEMA Regulatory Floodplain Information

SINGLE STRUCTURE PROTECTION

Plies, Columns, or Posts:

Minimize the structure's exposure to flood hazards

Eliminate obstructions to natural flow paths

Do not signijicantly affect flood flow hydraulics

Size and number of piles must be adequate to provide
structural support to building; must be embedded to
sufficient depth. and be adequately anchored to both the
structure and to subsoillbedrock to withstand scour and
erosion

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Figure 18.
A home .'.varlld on columns, JIIusrrat/ng how the are" 1M/ow the nrsl floor
should be 11m/red 10 parldng. liCe"., or .tol1lge. Ut/lltl.slInd mechanical
<</uJpn1fmt should ./so ". eiavat<<l above ground at INst to the dBpth
Indlc.ted on II>> FIRM.

Floodwalls or Berms:

Should only be used in very low veloc~iesldepths (sheet
flow veloc~y of iess than 5 feet per second/depth of less
than 3 feet); should only be used near toe offan or where
large sedimentation and debris loads are not likely

Should be able to resist erosion at base and below grade

Should be oriented to avoid diversion of hazards to
adjacent or down stream property

Can be effective when used as supplemental protection
for elevated structures

Since flood hazards threatening an individual site on an alluvial
fan are highly unpredictable, the methods used to safeguard a
structure will depend upon conditions unique to the location of
the site ~se~. II is therefore imperative to consult closely with
local engineering experts to determine the site's particular
physical conditions and expected flood and debris hazards.

"

Fill:

Should only be used in low to moderate veloc~y/depth
conditions

Must be armored above and below grade to w~hstand
scour. erosion, and debris impact and to protect the
structure's foundation

Should be oriented parallel to expected flood flow to
reduce debris damage, to avoid deflecling flow to adja-
cent or downstream property. and to minimize obstruc-
tion to fiow

Can be landscaped

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Figure 19.
Th/s home has bHn ./avat8d on Hrth fllIlInd lllndscll1>>d. The v~.ratIon
hiHps to stllbllln fh fill 10 protect It from MOslon.

Figure 20.
Floodwal/s, such as thi. exampl. In PhtHmlx, AriZona, should be con-
srruct~ para II.' to the 9XptJCrsd now dlr~tion to mlnlmlZII th. djv.rsion
of hazards onto IIdjllC.nt propsl1y.

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