FEMA Form FF-206-F Alluvial Fan Flooding (Form 6)

DEPARTMENT OF HOMELAND SECURITY

OMB Control Number: 1660-0016
Expiration Date: 1/31/2024

Federal Emergency Management Agency
ALLUVIAL FAN FLOODING FORM (FORM 6)
PAPERWORK BURDEN DISCLOSURE NOTICE

Public reporting burden for this form is estimated to average 1 hour per response. The burden estimate includes the time for
reviewing instructions, searching existing data sources, gathering and maintaining the needed data, and completing, reviewing, and
submitting the form. You are not required to respond to this collection of information unless it displays a valid OMB control number.
Send comments regarding the accuracy of the burden estimate and any suggestions for reducing this burden to: Information
Collections Management, Department of Homeland Security, Federal Emergency Management Agency, 500 C Street, SW,
Washington, DC 20472 , Paperwork Reduction Project (1660-0016). Submission of the form is required to obtain or retain benefits
under the National Flood Insurance Program. Please do not send your completed survey to the above address.

PAPERWORK BURDEN DISCLOSURE NOTICE
AUTHORITY: The National Flood Insurance Act of 1968, Public Law 90-448, as amended by the Flood Disaster Protection Act of
1973, Public Law 93-234.
PRINCIPAL PURPOSE(S): This information is being collected for the purpose of determining an applicant's eligibility to request
changes to National Flood Insurance Program (NFIP) Flood Insurance Rate Maps (FIRM).
ROUTINE USE(S): The information on this form may be disclosed as generally permitted under 5 U.S.C § 552a(b) of the Privacy Act
of 1974, as amended. This includes using this information as necessary and authorized by the routine uses published in DHS/FEMA/
NFIP/LOMA-1 National Flood Insurance Program (NFIP); Letter of Map Amendment (LOMA) February 15, 2006, 71 FR 7990.
DISCLOSURE: The disclosure of information on this form is voluntary; however, failure to provide the information requested may
delay or prevent FEMA from processing a determination regarding a requested change to a (NFIP) Flood Insurance Rate Maps
(FIRM).
Flooding Source:
NOTE: Fill out one form for each flooding source studied.

A. THREE STAGE ANALYSIS (Based on DHS-FEMA Guidance Document)
1. STAGE 1 ANALYSIS
A. The landform is composed of alluvium derived primarily from (check one):
Fluvial

Debris flow

Combination deposits

B. Source(s) of data used to determine composition, morphology, and location of the landform:
C. Is there an NRCS soils survey and soil survey map available?
Yes (If "Yes," please include a copy of the map and any pertinent sections of the soil survey)

No

D. Is there geologic mapping available?
Yes (If "Yes," please include a copy of the map and any pertinent geologic map unit descriptions)

No

E. Is there historic aerial photography available?
Yes (If "Yes," please include any copies of the site-specific photography)

No

2. STAGE 2 ANALYSIS
A. The alluvial fan landform exhibits:
Active

Inactive

A combination of active and inactive alluvial fan flooding

B. Approximate age of inactive fan surfaces (thousand of years):

years. Source of age estimate:

C. Is there an opportunity for avulsions that could lead to channelized or sheet flooding across the older fan surfaces?
Yes

No

Basis:

(

Hydraulic modeling

Geographic analysis

Other (Describe):

D. Is there geomorphic evidence of past avulsions during Holocene epoch?
Yes

No

FEMA Form FF-206-FY-21-105 (formerly 086-0-27E) (1/24)

Page 1 of 3

A. THREE STAGE ANALYSIS (Based on DHS-FEMA Guidance Document) (Continued)
2. STAGE 2 ANALYSIS (Continued)
E. Approximate age past avulsions:

years. Source of avulsion age estimate:

F. The active portion of the alluvial fan landform exhibits the following types of flooding (check one):
Flooding along stable alluvial channels

Sheet Flooding

Debris Flow

Unstable flow path flooding

G. The active portion of the alluvial fan landform exhibits the following types of flood processes (check one):
Recently active sediment deposition
High velocity flood flows

Recently active channels or floodplain erosion

Recent channel avulsions

Shallow sheet flooding

H. Methods used to support Stage 2 Analysis (check all that apply):
Geomorphic analysis

Field studies

Historical evidence

Hydraulic modeling

3. STAGE 3 ANALYSIS
A. The boundaries of the 1%-annual-chance floodplain have been determined using (check all that apply):
Risk-Based Analysis
FEMA FAN Program (if discharge at the apex is different than that given in the effective FIS, then attach MT-2, Form 2 along
with a plot of the flood frequency curve on log-normal probability paper and include the drainage area above the hydrographic
apex, and the mean, standard deviation, and skew coefficient of the Pearson Type III frequency curve)
List basis for evulsion coefficient used:
FAN used in:

Single

Multiple channel mode

Sheet Flooding Methods
Hydraulic Analytical Methods
List models & versions used:
Geomorphic Data, Post-Flood Hazard Verification, and Historical Information
Composite Methods (indicate which methods by checking above)
B. The active alluvial fan area has the following characteristics:
Highly active

Conical shape

Constructed channels

Unstable flow paths

Debris flow flooding

Entrenched stable channel networks

Undulating terrain

Urbanization (homes, roads, embankments, levees, railroads, canals, etc. that would after natural flow conditions)
C. Flooding sources elevated:
Flow from watershed above hydrographic apex
Method:
Flow from rainfall on fan surface
Method:
Flow from tributaries joining active fan area below hydrographic apex
Method:

B. STRUCTURAL FLOOD CONTROL MEASURES
1. The following structural flood control measures are proposed or built (check all that apply):
Channelization

Levee/Floodwall

Dam

Sedimentation Basin

Other:

2. Do the constructed or proposed structural measures affect flood hazards (including velocity, scour, and sediment deposition) on
other areas of the fan?
Yes
No
FEMA Form FF-206-FY-21-105 (formerly 086-0-27E) (1/24)

Page 2 of 3

B. STRUCTURAL FLOOD CONTROL MEASURES (Continued)
3. Attach completed Form 3 (Riverine Structures Form) for each structure.
4. Sediment Transport Considerations
Was sediment transport considered?
Yes (If "Yes," then fill out Form 3, Section F (Sediment Transport))
No (If "No," then attach your explanation for why sediment transport was not considered)
5. Please attach a copy of the formal Operations and Maintenance Plan.

C. MAPPING REQUIREMENTS
Attach a certified topographic work map showing the following:
The boundaries of the alluvial fan landform including: toe, topographic and hydrologic apexes, and lateral boundaries
The delineation of the active and inactive portions of the alluvial fan landform as determined by the Stage 2 analysis
The revised 1%-annual-chance floodplain boundaries, as determined by the Stage 3 Analysis, that tie into the effective floodplain
boundaries. Indicate where each delineation methodology used was applied if more than one methodology was used
The correct alignment of all structural features
The map scale and a north arrow

FEMA Form FF-206-FY-21-105 (formerly 086-0-27E) (1/24)

Page 3 of 3