Recommendations
NFPPR – ARID REGIONS
(Categorized by Priority) 12-1-14 SEB
Explanation/rationale
1. Mapping and regulation in arid regions:
(a)The NFIP should revise definitions, regulations,
and elevation requirements in arid regions for
existing Special Flood Hazard Area zones:
approximate Zone A in shallow sheet flooding less
than 1-foot deep, Zone AH in true ponding areas, and
Zone AO where depth exceeds 3 feet. The latter
category should be rezoned to Zone AE. This is
especially important in situations often encountered
in arid regions.
It is essential the mapping and regulation of floodplains
in arid regions be closely linked. Regulatory
requirements for various zones without a BFE should be
clearly stated for use in these regions.
(b) The NFIP should also clarify the elevation and
freeboard requirements above natural grade in
approximate Zone A, with no BFE (Refer to 44CFR
Parts 59.1, 60.3(b) and (c)).[FEMA, in conjunction
with state and local partners]
2. The NFIP and states should disallow, through more Areas subject to flow path uncertainty should be clearly
clear and strongly worded regulations, development dealt with in a manner to minimize increase in exposure
in areas subject to flow path uncertainty, erosion, and risk, as well as, minimize impacts on others.
and debris. These areas should be treated as
regulatory floodway. [FEMA, in conjunction with
state and local partners]
3. The NFIP and states should pursue the use of new
science and technology to update hydrologic and
hydraulic methods or models for arid regions
projects for determining the risk of flooding, erosion,
and debris flow hazards in arid regions, including
alluvial fans and post-wildfire conditions.
The
resulting predictions of depth and velocity should be
required to be verified with indirect methods at key
locations.[FEMA, in conjunction with state and local
partners and expert NGOs]
Due to unique circumstances prevalent in arid regions,
FEMA should encourage the use of stochastic numerical
models to better simulate location, extent, and depth of
flooding in areas of flow path uncertainty. Parallels
exist in other countries and their experience may be
applicable to arid regions in the US.
4. The NFIP should develop floodplain management Best management practices will vary as appropriate
techniques which address wildfire, flood and erosion amongst the arid regions.
cycle hazards experienced in the arid regions. [FEMA,
in conjunction with state and local partners and
expert NGOs]
NFPPR rec and explanation
Page 1 of 3
draft 12-01-14
5. Arid Regions R&D-The NFIP should resume the
needed arid regions research that was started with
the 1985 DMA Consulting Engineers report to FEMA
and the 1996 National Academy study. A starting
point for resuming this effort may include:
a. Review the effectiveness of present
identification, characterization, and
mapping guidelines in Appendix G.
Identify pros and cons.
b. Collect alluvial fan flooding mitigation
efforts utilized in the arid regions.
Establish post-construction performance
of these features. Identify pros and cons.
c. Establish specific aspects of both
Appendix G guidelines and mitigations
efforts which need improvement and/or
further research and development.
d. Establish,
in
light
of
recent
improvements in modeling software,
clear guidance and policy on the
applicability of different software on
active and inactive alluvial fan flooding
areas,
and
establish
different
classifications for use of these software
for different settings, if necessary and
appropriate.
e. Establish policy and guidance to ensure
that new technology used to determine
flood hazards is consistent with the local
and national floodplain requirements,
and is not improperly used (such as
ignoring the flow path uncertainty) to
allow development in areas where high
risk alluvial fan flooding is possible.
f. Coordinate with the Army Corps of
Engineers to develop guidance on the
appropriate
application
of
two
dimensional software (including the new
2D HEC-RAS) on alluvial fans and areas of
unpredictable flow paths. This would
produce defensible recommendations by
an organization with no conflicting
interests in the determination. [FEMA]
Continued research and development of models and
management approaches are essential in all flood risk
areas, but especially in arid regions, where the science
in newer and evolving.
6. Establish a streamlined process (through a LOMC or
other mechanism) for NFIP communities to update
FIRMs after major flood-disaster storm events cause
erosion and new flow paths that increase flood risks
Such a streamlined, process is even more important to
be promoted considering that in the past FEMA has
allowed delineation techniques to be used for alluvial
fans in arid regions that have failed to recognize flow
NFPPR rec and explanation
This would be a significant effort, but is essential if the
nation is to manage the increasing risk in arid regions of
the nation due to increased population and
development pressure.
Page 2 of 3
draft 12-01-14
vertically and/or change them horizontally. [FEMA]
NFPPR rec and explanation
path uncertainty. This resulted in unintentionally
reducing the extent of predicted Special Flood Hazard
Areas and/or under predicting volumes and depths of
flooding and debris.
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draft 12-01-14