ASFPM NFPPR 2015 – ARID REGIONS
(Categorized by Priority) 12-26-14
Recommendations
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.
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.
This is especially important in situations often
encountered in arid regions.
(b) The NFIP should also clarify the elevation and freeboard
requirements above natural grade in approximate Zone A, (b) Is this AR, or all floodplains? LL
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 clear
and strongly worded regulations, development in areas
subject to flow path uncertainty, erosion, and debris.
These areas should be treated as regulatory floodway.
[FEMA, in conjunction with state and local partners]
Areas subject to flow path uncertainty should be
clearly dealt with in a manner to minimize
increase in exposure and risk, as well as, minimize
impacts on others.
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 postwildfire 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]
4.
5. The NFIP should develop floodplain management
techniques which address wildfire, flood and erosion cycle
hazards experienced in the arid regions. [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.
6. Arid Regions Research &Development
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:
ASFPM NFPPR rec and rationale
Best management practices will vary as
appropriate amongst the arid regions.
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.
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draft 12-26-14
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 HEC-RAS) on
alluvial fans and areas of unpredictable flow
paths.
This would produce defensible
recommendations with no conflicting interests
in the determination.
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.
[FEMA, MitFLG, USACE, USGS, States, Expert NGOs]
7. 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 vertically and/or change
them horizontally. [FEMA, mapping partners]
ASFPM NFPPR rec and rationale
Such a streamlined, process is even more
important to be promoted considering that in the
past the NFIP has allowed delineation techniques
to be used for alluvial fans in arid regions that
have failed to recognize flow 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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