INSTRUCTIONS FOR FORM 6 - ALLUVIAL FAN FLOODING
[https://www.fema.gov/flood-maps/change-your-flood-zone/paper-application-forms/mt-2/instructions-form-6-alluvial-fan-flooding]


This form should be used for revision requests involving alluvial fan
flooding. 

DOWNLOAD FORM 6 - ALLUVIAL FAN FLOODING
[https://www.fema.gov/sites/default/files/documents/fema_form-6_alluvial-fan-flooding_ff-206-fy-21-105.pdf].

PURPOSE

In compliance with the National Flood Insurance Program regulations in
the Code of Federal Regulations Title 44 Section §65.13, this form is
used to ensure structural flood control measures in areas subject to
alluvial fan flooding is designed and/or constructed to provide 1%
annual-chance or greater flood hazard reduction. This is required for
FEMA to recognize it on a flood map.

Elevating a parcel of land or a structure by fill or other means will
not serve as a basis for removing areas subject to alluvial fan
flooding from an area of special flood hazards.  Complete engineering
analyses must be submitted in support of each section of this form.

In addition, it may be necessary to complete other forms relating to
specific flood control measures, such as levees/floodwalls,
channelization, or dams.

SECTION A: THREE-STAGE ANALYSIS

The three-stage analysis of alluvial fans is described in the Guidance
for Flood Risk Analysis and Mapping: Alluvial Fans
[https://www.fema.gov/sites/default/files/2020-02/Alluvial_Fans_Guidance_Nov_2016.pdf]
on FEMA’s website.  The document can also be downloaded on FEMA’s
Guidance
[https://www.fema.gov/media-collection/guidance-femas-risk-mapping-assessment-and-planning]
page on the website.  

 	* Complete the information regarding the characterization of the
alluvial fan landform.  This should include the material of which the
landform is generally composed.  Sources of data should also be
submitted.  To help the reviewer analyze the landform, the submitted
information should include, but not be limited to, soil surveys,
geologic mapping, and historic aerial photography.
 	* Complete the information regarding the definition of active and
inactive areas.  This section should be filled out to help correctly
determine the age of the alluvial fan, whether the fan is active and
inactive, the types of flooding, and the methods used to support this
analysis.
 	* Complete the information regarding the determination of the
1%-annual-chance floodplain boundaries.  This section should identify
the method or modeling that was used to delineate these floodplain
boundaries.  To help select the correct method for calculating the
1%-annual-chance floodplain boundary, the active alluvial fan
characteristics should be checked.  In addition, the flooding
source(s) should be evaluated so that additional flooding above or
below the hydrological apex is not ignored.

SECTION B: STRUCTURAL FLOOD CONTROL MEASURES

Complete the information regarding any structural flood control
measures.  In addition, complete and submit the Riverine Structure
Form 3 and an Operation and Maintenance Plan with the revision
request.  The Operation and Maintenance Plan may be submitted when
requesting a Conditional Letter of Map Revision, but it is not
required.  However, it will be required after construction is
complete and a revision to the Flood Insurance Rate Map is requested.

SECTION C: MAPPING REQUIREMENTS

Submit a certified topographic map showing the information indicated
in the Mapping Requirements section of the form. This includes the
boundaries of the alluvial fan landform, a delineation of the active
and inactive portions of the alluvial fan landform, the revised
1%-annual-chance floodplain boundaries and the correct alignment of
all structural features.  In addition, submit a copy of the effective
Flood Insurance Rate Map which is annotated to show the revised
1%-annual-chance floodplain boundaries.