HomeMy WebLinkAboutFDP201900006 Correspondence 2021-04-07Oti4XRr
NATIONAL FLOOD INSURANCE PROGRAM
FEMA PRODUCTION AND TECHNICAL SERVICES CONTRACTOR
ND SEGJ4
Mr. Scott R. Collins, P.E.
Civil Engineer
Collins Engineering
200 Garrett Street, Suite K
Charlottesville, VA 22902
Dear Mr. Collins:
April 7, 2021
IN REPLY REFER TO:
Case No.: 21-03-0459R
Community: Unincorporated Areas of
Albemarle County, VA
Community No.: 510006
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This responds to your request dated January 7, 2021, that the Department of Homeland Security's Federal
Emergency Management Agency (FEMA) issue a conditional revision to the Flood Insurance Rate Map
(FIRM) for Albemarle County, Virginia, and Incorporated Areas and the Independent City of
Charlottesville. Pertinent information about the request is listed below.
Identifier: Pleasant Green Subdivision
Flooding Source: Powells Creek
FIRM Panel Affected: 51003CO29D
The data required to complete our review, which must be submitted within 90 days of the date of this
letter, are listed on the attached summary.
If we do not receive the required data within 90 days, we will suspend our processing of your request.
Any data submitted after 90 days will be treated as an original submittal and will be subject to all
submittal/payment procedures, including the flat review and processing fee for requests of this type
established by the current fee schedule. The current fee schedule is available for your information on the
FEMA website at https://www.fema.gov/flood-maps/change-your-flood-zone/status/flood-map-related-
fees.
FEMA receives a very large volume of requests and cannot maintain inactive requests for an indefinite
period of time. Therefore, we are unable to grant extensions for the submission of required data for
revision requests. If a requester is informed by letter that additional data are required to complete our
review of a request, the data must be submitted within 90 days of the date of the letter. Any fees already
paid will be forfeited if the requested data are not received within 90 days.
If you have general questions about your request, FEMA policy, or the National Flood Insurance
LOW clearinghouse, 3601 Eisenhower Avenue, Suite 500, Alexandria, VA 22304-6426 / PH: 1.877•FEMA MAP
Compass, under contract with the Federal Emergency Management Agency, is a Production
and Technical Services provider for the National Flood Insurance Program
Page 2 of 2
Program, please contact the FEMA Mapping and Insurance eXchange (FMIX), toll free, at
1-877-FEMA MAP (1-877-336-2627). If you have specific questions concerning your request, please
contact your case reviewer, Mr. Michael Montague, by e-mail at montaguemc@cdmsmith.com or by
telephone at (303) 383-2306, or the Revisions Coordinator for your state, Ms. Ellie Pitney, by e-mail at
pitneyej@cdmsmith.com or by telephone at (303) 383-2318.
Sincerely,
Benjamin Kaiser, P.E., CFM
Revisions Manager
Compass PTSJV
Attachments:
Summary of Additional Data
MT-2 Form 1
CLOMR Notices Template
cc: Mr. Frank V. Pohl
County Engineer
Albemarle County
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Case No.: 21-03-0459R
NATIONAL FLOOD INSURANCE PROGRAM
Case No.: 21-03-0459R
FEMA PRODUCTION AND TECHNICAL SERVICES CONTRACTOR
Summary of Additional Data Required to Support a
Conditional Letter of Map Revision (CLOMR)
Requester: Mr. Scott R. Collins, P.E.
Community: Unincorporated Areas of Community No.: 510006
Albemarle County, VA
The issues listed below must be addressed before we can continue the review of your request.
1. Our review of MT-2 Application/Certification Form 1, entitled "Overview and Concurrence
Form," revealed that a community official for Albemarle County did not sign the second block of
Section D. Please submit a copy of Form 1 where the second signature block has been signed by a
community official (preferably the Floodplain Administrator). Please find the Tillable form
required attached.
2. This CLOMR request will be processed by the Federal Emergency Management Agency (FEMA)
only after FEMA receives documentation from the requester that demonstrates compliance with
the Endangered Species Act (ESA). Our review revealed that the submitted ESA documentation
is dated December 16, 2016, and references that it expires one year after the date. For projects
that are not constructed, funded or permitted by a federal agency, the requester must demonstrate
ESA compliance by submitting to FEMA written justification that a "Take," meaning to harass,
harm, pursue, hunt, shoot, wound, kill, trap, capture, or collect, or to attempt to engage in any such
conduct, has no potential to occur to threatened and endangered species present in the county as a
result of the project. If a project has the potential to "Take" listed species, an Incidental Take
Permit may be submitted with justification that the project is the subject, or is covered by the
subject, of the permit.
For projects with federal construction, funding, or permitting, a "not likely to adversely affect"
determination with concurrence from the National Marine Fisheries Service or the U.S. Fish and
Wildlife Service (the Services), a "No Effect'' determination from the federal action agency, or
other approval from the Services is acceptable documentation of ESA compliance. This
documentation must be coordinated by the federal agency engaging in the construction, funding,
or permitting of the project and the Services, as appropriate.
LOMC Clearinghouse, 3601 Eisenhower Avenue, Suite 500, Alexandria, VA 22304-6426 / PH: 1-877-FEMA MAP
Compass, under contract with the Federal Emergency Management Agency, is a Production
and Technical Services provider for the National Flood Insurance Program
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3. Our review revealed that the modeling of the existing culvert at Cling Lane appears to be different
from the effective model. Please submit certified (sealed, signed, and dated) as -built plans or
surveys for each hydraulic structure included in the hydraulic analysis that is modeled differently
from the effective model. The plans should include the dimensions of the culvert such as length,
size, upstream and downstream invert elevations, and all other elevations necessary for
verification of the hydraulic analysis. Also, please ensure that the vertical datum such as the North
American Vertical Datum of 1988 (NAVD 88) or the National Geodetic Vertical Datum of 1929
(NGVD 29) is referenced on each plan. Alternatively, please show the required information of the
existing culvert on the certified work map and then a separate plan is not required. If the modeling
of a structure has changed from the effective analysis, please revise MT-2 Form 3, entitled
"Biverine Structures Form," to include this information.
4. Our review revealed that the proposed plan titled "Stream Crossing Road Plan & Profile," for the
culvert crossing at Rambling Brook Lane does not include all of the necessary information to
verify the hydraulic modeling. The plans should include the dimensions of the culvert such as
length, size, upstream and downstream invert elevations, and all other elevations necessary for
verification of the hydraulic analysis. Also, please ensure that the vertical datum such as the
NAVD 88 or the NGVD 29 is referenced on each plan. Alternatively, please show the required
information of the proposed culvert on the certified work map and then separate plan is not
required.
5. Our review revealed that LOMR Case No. 20-03-1533P, will become effective June 23, 2021, and
is located in the same vicinity as your submittal. Please obtain the model from LOMR Case No.
20-03-1533P from the FEMA Engineering Library and use this model as a base for your revised
model. Please do not truncate the model. If unintended changes occur outside of the revised area,
please use the version of HEC-RAS used to prepare the effective model. To request information
from the FEMA Engineering Library, visit the website httos://www.fema. og v/en ineerin -library
and follow the directions. Please note that the copy of the effective model that you receive from
the Engineering Library is considered to be the duplicate effective model and label it as Duplicate
Effective model in the submission.
6. Our review of the submitted proposed conditions Hydrologic Engineering Center's River Analysis
System HEC-RAS 5.0.6 hydraulic analysis revealed the following issues. Please submit a revised
hydraulic analysis that corrects these issues and provide digital copies of the input and output files
for this model. Please show the vertical datum such as the NAVD 88 in the description box of the
HEC-RAS model.
a. Subparagraph 65.6(a)(2) of the National Flood Insurance Program (NFIP) regulations states
that to avoid discontinuities between revised and umevised flood data, hydraulic analyses must
have a logical transition between revised elevations of the 1-percent-annual-chance (base)
flood and those developed previously for areas not affected by the revision. Please ensure that
the revised base flood elevation (BFE) ties —in to the effective BEE within 0.5 foot, or within
0.0 feet if practical, at the upstream and downstream ends of the revised reach. Please extend
the hydraulic analysis upstream until BFE tie-in is achieved. Please note that the work map
will need to be extended upstream as well along with the contours, flood hazard delineations
and cross section labels and locations.
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Case No.: 21-03-0459R
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b. Our review revealed that the 0.2-percent-annual-chance water -surface elevations (WSELs) are
higher than the endpoints of Cross Sections 3932.07 and 3891.62 in the submitted proposed
conditions hydraulic analysis along Powells Creek. The use of vertically extended cross
sections might both overestimate the WSEL and underestimate the width of the floodplain.
Please revise the cross section geometry coordinates so that the end points of all cross sections
are equal to or extend higher than the corresponding WSEL.
c. Typically, culvert section 2 is located a short distance downstream of the culvert, and culvert
section 3 is located a short distance upstream of the culvert so that the topography of the
structure or embankment is not captured for the computation. Please revise Sections 2 and 3,
which occur at Cross Sections 908.45 and 1021.3, so that they are located at appropriate
distances from the culvert inlet and outlet and do not capture the topography of the structure.
d. Our review revealed Mannings "n" values do not appear to be indicative of natural conditions.
The overbanks use a Manning's "n" less than the channel. Typically, the channel Manning's
"n" are less than the overbank to represent natural conditions. Please revise the Manning's
"n" values to reflect natural conditions, or provide an explanation why the values in the model
were chosen.
e. Our review revealed that the WSEL profiles that correspond to the 0.2-percent-annual-chance
flood and base flood cross each other at Cross Section 1651.13 of Powells Creek. Please
revise the submitted hydraulic model to properly reflect the WSELs for each flood event so
that they do not cross.
f. The ineffective flow area option should be used when low flow occurs at a structure. Our
review of the submitted existing and proposed HEC-RAS models indicates that low flow
occurs at the structure located at Cling Lane at Cross Section 3861.37. Please revise the
submitted models at Cross Sections 3831.12 and 3891.62, to account for ineffective flow
areas outside the main channel, or provide an explanation why this is not necessary.
g. According to the HEC-RAS Technical Reference Manual, prepared by the U.S. Army Corps
of Engineers, dated November 2002, the typical contraction and expansion loss coefficients
are equal to 0.3 and 0.5, respectively, culverts where there are more abrupt transitions (as are
typical at bridge/culvert Sections 2, 3, and 4) such as Cross Sections 3831.12, 3891.62, and
3932.07, and equal to 0.1 and 0.3, respectively, at other cross sections where there are more
gradual transitions (including bridge and culvert Sections 1 and 5). Please revise the
contraction and expansion coefficients at Cross Section 3791.09 so that they are 0.1 and 0.3,
respectively, or provide an explanation as to why they are set higher than typical values.
h. Our review revealed that the encroached (floodway) profile is included with the multiple
profile plan in the proposed conditions model. Please create two separate plans; the multiple
profile plan and the floodway plan. The floodway plan should only include the encroached
(floodway) and unencroached (natural) base flood profiles. The unencroached profiles for the
proposed conditions floodway plan should be exactly the same as the base flood profile in the
proposed conditions multiple profile plan.
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Case No.: 21-03-0459R
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i. Our review revealed encroachments were not placed within the floodway profile in the
submitted proposed conditions plan. Please place encroachment stations at every cross
section within the revised area. Please ensure that the floodway is hydraulically smooth,
surcharges remain between 0.0 feet and 1.0 foot, and the encroachment stations are located in
the flood fringe, the area between the channel banks and the boundary of the base floodplain.
The floodway analysis should also start with Method 4, with "equal conveyance reduction"
checked. Then, the analysis should be imported into Method 1 so that the encroachment
stations can be adjusted as needed
7. The submitted proposed conditions topographic work map, titled "Pleasant Green Subdivision —
Floodplaln Study," Sheet 3, prepared by Collins Engineering, certified December 2, 2020, does
not provide some of the essential information required to complete our detailed review of this
request. Please submit a revised topographic work map, certified by a registered P.E., which
shows all applicable items listed in Section C of Application/Certification Form 2, entitled
" Riverine Hydrology and Hydraulics Form," including the following information. Please ensure
that there is consistency between the work map, revised proposed hydraulic model, and the
annotated Flood Insurance Rate Map (FIRM).
a. Please show and label the boundary delineations of the currently effective base floodplain,
0.2-percent-annual-chance floodplain, and regulatory floodway as they are shown on FIRM
panel 51003CO29D. For clarity, please show effective and proposed delineations in different
line types and colors. Please do not use shading.
b. Our review revealed that effective LOMR Case No. 20-03-1533P, will become effective June
23, 2021, and partially overlaps the area to be revised. Please ensure that flood hazard
delineations from LOMR Case No. 20-03-1533P are shown as the effective delineations on
the work map. Please ensure that the proposed flood hazard delineations tie-in to the
delineations from LOMR Case No. 20-03-1533P at the downstream end of the revised reach.
c. Please ensure that the proposed floodway delineation is shown hydraulically smooth in
between the cross sections. At the cross sections it is delineated based on the encroachment
stations set. Please update the proposed base and 0.2-percent-annual-chance delineations also
as per the updated proposed model asked above for the entire revision area until upstream
vertical tie-in is achieved. The submitted work map shows the revised delineations until
Cross Section L (Cross Section 3384.41) only. Please extend the limits of the work map to
cover the entire revised hydraulic model revision area.
d. Please ensure that the graphical tie-in shown on the work map corresponds to the location of
the vertical tie-in in the proposed hydraulic model. Please show and label the graphical tie-
ins between the proposed and effective flood hazard boundary delineations at the upstream
and downstream ends of the revision area. Please ensure that the revised delineations tie-in
directly to the effective delineations and that the tie-ins occur a short distance upstream of the
upstream most cross section, and a short distance downstream of the downstream most cross
section.
e. Please ensure that all cross sections used in the hydraulic model are shown and labeled the
same way they are in the hydraulic model. Please also ensure all cross sections are shown
crossing the entire revised 0.2-percent-annual-chance floodplain.
f. Please show the proposed contours for the project area and show them in darker shade than
the existing contours outside the project area. Please also show how the proposed contours
merge with the existing contours outside the revision area.
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Case No.: 21-03-0459R
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g. The topwidths of the base floodplain computed in the proposed conditions hydraulic model
do not match the floodplain topwidths shown on the topographic work map at the cross
sections listed below. Please revise the work map or hydraulic model as appropriate to
resolve these discrepancies. The geometry of the cross sections in the proposed conditions
hydraulic model should reflect the topography shown on the work map.
Powells Creek
Base Flood lain To width feet
Cross Section
Model
Ma (approx.)
3384.41
119
55
2959.02
119
78
2559.86
153
107
1021.3
258
258
908.45
229
59
h. Please continue to show the flow line (profile baseline) used in the hydraulic model. Our
review revealed discrepancies between the reach lengths shown on the topographic work map
and the reach lengths used in the submitted hydraulic HEC-RAS models at the following
cross sections. Please resolve these discrepancies and submit revised topographic work maps
or revised models as appropriate. Please ensure that the reach lengths between cross sections
shown on the work map match the reach lengths given in the submitted hydraulic models.
Powells Creek
Reach Len th feet
Cross Section
Model
Ma (approx.)
2559.86
580
609
562.24
360
298
i. Please ensure consistency between the information presented on the topographic work map
and that shown in the hydraulic model, including the cross section geometry used in the
hydraulic model should match the topography shown on the work map.
j. Please show the north arrow and reference vertical datum such as NAVD 88 or NGVD 29 on
the work map.
8. To assist our review and to expedite processing of this request, please provide digital Geographic
Information System (GIS) that reflect the revised topographic work map. If GIS data is not available,
Computer -Aided Design (CAD) data may be submitted. Please ensure the digital data are spatially
referenced and cite what projection (coordinate system, example: Universal Transverse Mercator
[UTM]/State Plane) was used, so that the data may be used for accurate mapping. The important data
to show on the digital work map are the contour information, the stream centerline, the cross section
lines, the road crossings and hydraulic structures, the proposed flood hazard delineations and the tie-
in locations. Everything should be clearly labeled and all information should be contained within the
drawing and not externally referenced.
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Case No.: 21-03-0459R
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9. Please submit an updated annotated FIRM that shows the revised boundary delineations of the base
floodplain, 0.2-percent-annual-chance floodplain, and regulatory floodway as shown on the updated
work map and how they tie-in to the boundary delineations shown on the effective FIRM at the
downstream and upstream ends of the revised reach on the issued LOMR 20-03-1533P FIRM panel.
Please use different colors to differentiate the proposed and effective boundary delineations and
ensure that the effective floodplain boundaries are visible through the proposed linework (i.e. do not
use fill). Also, please show the title block of the effective FIRM on the annotated FIRM.
10. Our review indicates that the proposed project encroaches upon a regulatory floodway and may cause
increases in BFEs. Please provide evidence that the proposed project satisfies the requirements of
Section 65.12 of the National Flood Insurance Program (NFIP) regulations, including the items stated
below. A copy of Part 65 of the regulations can be accessed at httos://www.ecfr. ov/cgi-bin/text-
idx?c=ecfr&tpl=/ecfrbrowse/Title44/44cfr65_main_02Ttpl.
a. Evaluation of alternatives which would not result in any increase in BFEs and an explanation why
these alternatives are not feasible.
b. Documentation that individual legal notices have been sent to all property owners affected by the
increases in BFEs due to the proposed project. Documentation of legal notice may take the form
of a signed copy of the letter sent and either a mailing list or certified mailing receipts. The
attached Combined CLOMR Notice template may be used to prepare the legal notice. Prior to
distribution, please submit a draft copy of the notice for verification of content.
c. Certification by a registered P.E. that no structures are located in areas which would be impacted
by the increased BFEs due to the project.
11. Our review indicates that the Letter of Map Revision (LOMR) that follows this CLOMR will
revise the flood hazard information along Powells Creek. Please submit documentation that
affected property owners have been notified of the proposed flood hazard revisions information
(i.e., revise base [1-percent-annual-chance] flood elevations, the base flood floodplain and
regulatory floodway). Documentation of legal notice may take the form of a signed copy of the
letter sent along with either a mailing list or certified mailing receipts. The individual legal
notices must include the extent of the proposed revision and contact information for any interested
parties and must also mention the community's intent to revise the regulatory floodway. The
individual legal notices must be sent on community letterhead or the community must provide a
statement confirming that all affected property owners have been notified of the proposed
floodway revision. Please submit a draft copy of the notification for verification of content,
prior to distribution. One of the attached templates may be used to prepare the draft notification.
Please upload the required data using the Online LOMC website at
https:/Awards.fema.gov/femaportal/onlinelome/signin.
For identification purposes, please include the case number referenced above on all correspondence.
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Case No.: 21-03-0459R