National Flood Policy—ASFPM 2015 Recommendations
M. Arid Regions
Recommendations
Mapping and Regulation in Arid Regions
M-1 STANDARDS RELATED TO ARID REGION ISSUES
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.
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)).
See: F-1
[FEMA, in conjunction with state and local partners]
M-2 The NFIP and states should disallow, through clear and
strongly worded regulations, development in areas subject to
flow path uncertainty, erosion, and debris. These areas should
be treated as regulatory floodway.
See: A-10, A-11, F-10
[FEMA, in conjunction with state and local partners]
M-3 HYDROLOGIC AND HYDRAULIC MODELS
a) The NFIP and states should pursue the use of new science
and technology to update hydrologic and hydraulic methods
or models for arid regions when determining the risk of
flooding, erosion, and debris flow hazards in arid regions,
including alluvial fans and post-wildfire conditions.
b) The resulting predictions of depth and velocity from a)
should be required to be verified with indirect methods at
key locations.
Explanation/rationale
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.
While these zones and issues apply to areas other
than arid region areas, there are especially
important in situations often encountered in arid
regions.
Areas subject to flow path uncertainty should be
clearly dealt with in a manner to minimize
exposure and risk, as well as, minimize impacts on
other properties and people.
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.
See: A-10, A-11
[FEMA, in conjunction with state and local partners and
expert NGOs]
M-4 The NFIP should develop floodplain management Best management practices will vary,
techniques which address wildfire, flood and erosion cycle appropriate, amongst various arid regions.
hazards experienced in the arid regions.
[FEMA, in conjunction with state and local partners and expert
NGOs]
Arid Regions Research & Development
M-5 RESUME NFIP R & D FOR ARID REGIONS
There is a critical need to resume the 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:
NFPPR policy rec and explanations
Page 1 of 2
as
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.
Section M Arid Regions
draft 1-28-15
National Flood Policy—ASFPM 2015 Recommendations
a) Review the effectiveness of present identification,
characterization, and mapping guidelines in Appendix G.
Identify pros and cons.
b) Collect data on alluvial fan flooding mitigation efforts utilized
in the arid regions. Develop options for post-construction
performance of these features; identify pros and cons.
c) Identify 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 and other
agencies to develop guidance on the appropriate application
of two-dimensional software (including the new 2D HECRAS) on alluvial fans and areas of unpredictable flow paths.
This would produce defensible recommendations with no
conflicting interests in the determination.
[FEMA, MitFLG, USACE, USGS, States, Expert NGOs]
M-6 Establish a streamlined process (through a LOMC or other
mechanism) for NFIP communities to update FIRMs after major
flood-disaster storm events that cause erosion and new flow
paths that increase flood risks vertically and/or change them
horizontally.
See: A-10, A-11
[FEMA, mapping partners]
NFPPR policy rec and explanations
Page 2 of 2
This would be a significant effort, but is essential if
the nation is to manage the increasing risk in arid
regions of the nation where we see greatly
increased population and development pressure—
thus increased risk.
Such a streamlined process is critical considering
that in the past the NFIP has allowed delineation
techniques to be used for alluvial fans in arid
regions that failed to recognize flow path
uncertainty. This results in unintentionally
reducing the extent of predicted Special Flood
Hazard Areas and/or under predicting volumes
and depths of flooding and debris.
Section M Arid Regions
draft 1-28-15