Alexander Ct-CS080902Page 1 of 3
Ken Griffin - RE: Floodplain
From: "Dan Buhman" <dan.buhman @buhwater.com>
To: "'Ken Griffin "' <kgriffin @ci.coppell.tx.us>
Date: 9/2/2008 12:09 PM
Subject: RE: Floodplain
Ken,
Sorry I wasn't clear in the letter. Let me try to clarify here.
The `n' value in the original flood study was 0.08, so the fence will not cause any adverse impact because it will
not raise the `n' value above what it is already. When I modeled the n =0.09 versus n =0.08, I was trying to do a
sensitivity analysis to raising the `n' value; it showed very little (0.01) to 0.00 change.
Because there is no change to the `n' value (because of the heavy riparian vegetation on the bank), I felt that
adding cross sections would not be beneficial and would not produce any additional accuracy to the study. I
completely agree with your requirements when the `n' value is increased but felt it was not needed here
because of the existing conditions.
Let me know your thoughts and I will modify the letter to clarify.
Thanks,
Dan Buhman, P.E.
Buhman Associates, LLC
Mobile: 214 - 864 -1555
dan.buhman@buhwater.com
From: Ken Griffin [mailto :kgriffin @ci.coppell.tx.us]
Sent: Tuesday, September 02, 2008 11:26 AM
To: Dan Buhman
Subject: RE: Floodplain
Dan
Not sure I followed what you proposed. It looks like you are comparing the fence encroachment to a
run that changes the 'n' value from .08 to .09. The comparison I'm looking for is comparing the fence
encroachment to the existing study, using whatever 'n' value that was used in the existing study. If the
existing study used .035, then you should compare that to the fence encroachment 'n' of .08.
In the other situations that I have allowed this approach, I have required that the original flood study be
file: HC: \Documents and Settings \radloo \Local Settings \Temp \XPgrpwise \48BD2CFCCity... 2/22/2010
Page 2 of 3
used as a base line. Then, the consultants have added new cross - sections to accurately depict the
existing field conditions in the area to be fenced. Then, a new study was run to compare the existing
study to the new study, which includes new cross - sections and a new 'n' value for their side of the creek
of .08. The information submitted to my office includes the original study, the revised study and a
table comparing the differences throughout the entire reach of the original study.
Based on what you have submitted, I can not approve any encroachment into the floodplain.
Ken,
Thanks for your consideration of this request for a waiver for construction of a security fence within the
Grapevine Creek floodplain. Please see the attached PDF file containing the letter report and appendices.
If you have any questions, please feel free to contact me any time.
Thanks,
Dan Buhman, P.E.
Buhman Associates, LLC
Mobile: 214 - 864 -1555
dan.buhman@buhwater.com
From: Ken Griffin [ mailto :kgriffin @ci.coppell.tx.us]
Sent: Wednesday, August 13, 2008 8:31 AM
To: Dan Buhman
Subject: Re: Floodplain
The "n" value that has been used for studies to determine the impact of wrought iron fences in the
floodplain is 0.08, in lieu of 0.035.
Ken Griffin, P. E.
Director of Engineering & Public Works
972 - 304 -3686
kgriffingci. coppell.tx.us
Ken Griffin, P. E.
Director of Engineering & Public Works
972 - 304 -3680
kgriffingci. coppell.tx.us
>>> "Dan Buhman" <dan.buhmangbuhwater.com> 8/12/2008 5:31 PM >>>
Ken,
We spoke a few weeks ago about some landowners that want to build a fence in the floodplain at the
file: HC: \Documents and Settings \radloo \Local Settings \Temp \XPgrpwise \48BD2CFCCity... 2/22/2010
Page 3 of 3
NW corner of Denton Tap and Bethel. I have received the model from Nathan Maier and am ready to
start looking at the impact of the fence. You had said that you could send me the Manning's 'n'
values that you recommend to show that impact. Can you send me your criteria? I'll put it in the
model and send you a short memo summarizing the findings.
Thanks,
Dan Buhman, P.E.
Buhman Associates, LLC
211 Cherrybark Drive
Coppell, TX 75019
Mobile: 214 - 864 -1555
dan.buhman @buhwater.com
file: HC: \Documents and Settings \radloo \Local Settings \Temp \XPgrpwise \48BD2CFCCity... 2/22/2010
September 2, 2008
City of Coppell
Department of Engineering and Public Works
Attn: Mr. Ken Griffin, P.E., Director
255 Parkway Blvd.
P.O. Box 9478
Coppell, TX 75019
Subject: Request for Waiver for Construction of Security Fence within Floodplain
Mr. Griffin:
&4W &,F&*&f
b r ae
I have been retained by the owners of Lots 11 and 12 in the new Alexander Court development to evaluate the
feasibility of constructing a wrought iron security fence on their property and within the floodplain of Grapevine Creek
(FIRM Map Number 48113C0155 J, Panel 155 of 725). The properties in question are upstream (west) of Belt Line
Road and north of West Bethel Road, effectively at the northwest corner of this intersection. After review of the
LOMR and HEC -RAS model, site visits, and conversations with you, I conclude the following:
■ The riparian vegetation on the right bank of Grapevine Creek on lots 11 and 12 is of sufficient density and type to
warrant the use of a 0.08 Manning's "n" value. This value was used in the LOMR study.
■ Construction of a wrought iron security fence parallel or perpendicular to the floodplain will not raise the "n" value
above the current 0.08.
■ Construction of this security fence will not cause a change to the effective 100 -year floodplain modeling or
modeled water surface elevations
Fence Plans
The homeowners understand the restriction to not place any structure within the floodplain and plan to construct the
security fence to keep small children away from Grapevine Creek's steep banks and to increase the usable open
space on the property. The fence will run parallel to the creek flow and within the riparian vegetation zone (brush,
trees). Perpendicular sections will connect to the front of the property (or close to the house) with only a small
section in the floodplain. The homeowners are prepared to construct a fence of type and vertical unit spacing as to
conform to the results in this analysis.
Riparian Vegetation
The images below show the riparian vegetation, which I classify as medium -to -dense brush with trees. The n value
for such vegetation ranges from approximately 0.06 to 0.1. In these images, the n value could be 0.1.
Letter- Floodpla inFenceExemption_09022008.doc
Request for Waiver for Construction of Security Fence within Floodplain
September 2, 2008
Page 2
Image 1 - Looking Approximately North from Lot 11, Man Standing at Floodplain Boundary
Image 2 - Looking West from Northeast Lot 11 Floodplain Boundary
Letter- Floodpla inFenceExemption_09022008.doc
Request for Waiver for Construction of Security Fence within Floodplain
September 2, 2008
Page 3
Image 3 - Looking West from Lot 11, Man Standing at Floodplain Boundary
This analysis of the LOMR, floodplain mapping, site conditions, and hydraulic modeling indicates that a wrought iron
security fence constructed on Lots 11 and 12 will not cause a change to the effective 100 -year floodplain modeling or
modeled water surface elevations. Therefore, we request a waiver so that construction of this fence may proceed.
Thank you for your consideration. The attached Appendices provide additional detail into the analysis:
■ Appendix A: FIRM Map Number 48113C0155 J, Panel 155 of 725, Date August 23, 2001
■ Appendix B: City of Coppell, Dallas County, Texas, Grapevine Creek LOMR Effective April 24, 2008
■ Appendix C: Alexander Court Survey
■ Appendix D: Smaller Scale of Alexander Court Survey with Focus on Lots 11 and 12
■ Appendix E: HEC -RAS Output
Letter- Floodpla inFenceExemption_09022008.doc
Request for Waiver for Construction of Security Fence within Floodplain
September 2, 2008
Page 4
If you have any questions or concerns, please do not hesitate to contact me at any time.
Sincerely,
Daniel L. Buhman, P.E. Texas 96237
President
Buhman Associates, LLC.
cc: Mr. Dayton Judd
Mr. Colin McGrady
Letter- Floodpla inFenceExemption_09022008.doc
Appendix A
FIRM Map Number 4811300155 J, Panel 155 of 725, Date August 23, 2001
r — _ — — � �i _ i � P vs
�51
FT
tit
I I
z z z z
0 0 0 2 ull -
0 0 0 o o 0
E u
CIA
0 10i
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W— cm
z I� a s ° c. , , F � Y W
Appendix B
City of Coppell, Dallas County, Texas, Grapevine Creek LOMR Effective
April 24, 2008
NR
N IV T)
Federal Emergenoy Manage.
washin b.c. 20472
MAR 2 42008
CER TTFIED MAIL
REIN RECEIPT REQUESTED
The Honorable Douglas N. Stover
Mayor, City of COPP61
P.O. Box 9478
oppell, TX 75019
D ear Mayor Stover:
IN REPLY REFO
Case N1 '0.*
ommumit Name:
C ommunity o � 4
]Effective Oats of
This Revision:
M AR 2 8
07 -06 -0
City of C oppell, TX
480170
APR z 4 2008
The Flood Insurance Study report and Flood Insurance Rate Map for your cc nianity have been revised b
this Letter of Map Revision (LDMR). Please use the enclosed ann otated neap panel (s) revised by this
LOMR for fioodplain naagernnent purposes and f or all flood it surance policies and renewa issue in yo ur
coma unit .
Additional documents are enclosed which pry de information regarding this L MR. please s the List of
Enclosures below to deterrn e w hich dociimcnts arc incl uded. Other attachments s peci fi c to this request
may bc included as referenced in the Detemiination Document If you have any questions regarding
ocdpl ain management re gulations for your co mmuruty or the National Flood Insurance `ognm (NFIP) to
general, please coact the Consultation Coordination Officer for your co=u,nit * if you have any
technical questions regarding this LO , please contact th Director, Mitigation Division of the
Department of Homeland Se cunhy's Federal E mergency Management Agency (FEMA) in Denton, Texas, at
(940) 899-5127, or the FE1 A Map Assistance Center toll f ree at 1-877-336-2627 (1-877-FEMA MAP).
Additional information ormation about the lFIP is available on our websitc at http://www.fema.gov/i
suacerely,
; 4'W' 'A. W
Joshua A. Smith, C FM, Progm - tn Specialist
agineering Management Branch
Mitigation Directorate
List of Enclosures:
Letter of Map Revision Deters nation Document
Annotated Flood. In surance Rate Map
Annotated Fl ood Insurance Study Deport
cc: Mr. Ken Griffim, P.E.
Di rector of Engineering
Public Works
City ofCopell
l~ on William t Blanton Jr., CFM, Chief
Engi,neeritng Management Branch
Mitigation Directorate
Mr. l ichacl R. B oyd, P.E.
Executive Vice President
Nathan D. Mater Co n su lting Engineers, Inc.
Pa I O f 4 I issue Date. M 2 4 2008 Effective D ate; APR 2 4 2008 C ase No.; 07-06-22 . .................... � LOMR -APP
Fr 1 e rr WW h
Federal Emer Mana A
ND Chinon, D.C 20
•A r�,rs �'�
LETTER OF MAP REVISION
DETERMINATION DOCUMENT
COMMUNITY AND RE�WC N INFORMATION
City of Coppett
Dallas C oun ty
Texas
COMMUNITY
COMMUNITY NO.: 4
IDENTIFIER Qrspevirte Creep
ANNOTA MAPPING ENCLOSURES
TYPE: FIRM* NO,! 461130DI 55 J DATE: August 23 2001
TYPE: F1R 41 NO.'. 481 1 300 135 J DATE: August 231 2001
PROJECT DESCRI
BRIDGE
13AS18 OF REOUP-ST
FLOODAY
HYDRAULIC ANALYS
NEW TOPOGRAPHIC DATA
APP ROXIMATE LATU O & Lo NGtTUDE - - 32.67 - 97.014
SOURCE: USGS QUADRANGLE DATUM: NAD 27
ANNOTATED STUDY ENCLOSURES
DATE OF EFFECTWE FLOOD INSURANCE STUDY REMPO T: June 16, 2005
PROFILE(S): 212P, 213P en d 2 16P
FI,.00 DWAY DATA TAE3L F;; 8
ACI DSuras ralliact cn-Mgais to floodIng source affected by this mvision.
FIRM - Flood tnsuranm Rate leap; ',* FBFI # Flood 8 oundary and Roadway Map; ` FFIS - Flood Lazard Boundary Map
FLOODING SOURCES I & REVISED REACH(ES)
Grapevine Creek - #rdm ppraximate 1 .650 feet down stream of Dent�an Tap Road to approximately 1 feet � ovm$trearn 0 1 qt, Lome Sc hvtestern Railway
Tributary -t of GrapevIm C me i frorn j ust upstream Of the C D nfl;u e nce viIth Grapevine Creck to a ppro )dm atel y 800 feet upstrearn
Flooding Soursx
Grapevine Creek
Tributary i of Grapevine Creek
• SFE5 - Base FroQd Eleuiaona
SUMMARY OF REVISIONS
Effectilve Flooding
Revised Flooding
Zone AE
Zone AE
F'toodway
Flood- y
SFEs`
BFEs
BFEs
6FEs
11 0149 # 8111 ilk V11 it o k
Increases
ureaae:s
Yes
YES
YES
YES
ONE
YES
ONE
YES
This docume provides the determ ination frorn the Department of Homeland Security's Federal Emergency Manag Agency (F A)
regarding a request fora Letter of Map Revision (LOMR) #er the area described above. Using the information submitted, we have determined that
a revis to the flood hazards depicted in the Flood Insurance Study (F I ) report and /or Nati onal Flood 1 nsuran re Program (N F[P) reap is
warranted, This document revises the affective NFIP map, as indicated in the afkached documentation. please use the encl annotated map
panels reprised by this LOMB for f oodplain manag purposes an d f all flood insurance p and renewals in your cammunity.
TThIs determination 1s based on the flood data presently avaiiabla. The en cased documents provide additional information regarding this determination. If you have
any questions about this document, please contact the FEMA Map Asslstsnce Center toll free at 1. (1- 877 -FE A MAP) qr by Wet addressed to th
LOM R depot. 360 Eisenhower Avenue, Aloxand rla, CIA 2-2304. Add Itlonal Inform atf -on abo ut t NF IR is available GrT u ur website at h1tp I/myw. fema.goyinfip.
Joshua A. Smith, CF M, Prog �Spegi
Engineering Management Branch
M itigation Directorate
11 2553 10,3.1.07D62203 t 02 - 1-A,
Page 2 of 4 Issue Daie: � 3 42008 Effective Date: APR 2 4 2W6 ] Casa Igo.: 07- 06 -2203P I I,OMR -APP
a
Federal Emergency Management Agency
°+ Washington, D.C. 20472
LETTER OF MAP REVISION
DETERMINATION DOCUMENT (CONTINUED)
COMMUNITY INFORMATION
APPLICABLE NFIP RE ULATIONSI oMM 'NffY OBLIGATIO
We have made this determination pun. uant to Section. 206 of the Flood Disaster Protection Act of 1973 .L- 3 -234) and in accordance
with the National Flood Insurance A ct of l 968,. as anncnded Title X11I of the Housing and Urban, D elop ent Act of 196 F.L. 90
42 U.S. 400 128, and 44 CPR Part 65 Pursuant to Section 1361 of the rational Flood Trommee Act of 1 968, as amended
oommunics participating in the NFIP are - re q u ire d to adopt and enforco floodplam' management reulation.s that meet F"IP
izitofia. These cx a, including adoption o f the FIS mport an FIRM* and the modifications, arraade by this T.0NL K ar e the i munr
rcquj.Tements for cunt ued NFIF participadon and do not supersede more stringent State or local requiremcnis to which the regulations
aply-
l'e provide the flood"y design ation to your community as a tool to regulate floodplain d Wh erefore, the flood revision
we have degc beds in this letter, w hite acceptable t o us, must also be acceptable to your community and adopted by appropriato
communi action, as specified in Paragraph 60.3(d) of the NFIP regulations.
NFIP regulations Subparagraph 60.3(b)(7) requires communities. to cns c that the flood - carrying capacity witbin, the altered or relocated
- )moon of any waterco�um is maiaatairned_ This provision ii i into y our commum€ ~s existing oodplam management
frd€ nces- the fore, respo f maint anoc of the altered or relocated watercourse, including any related appurtenances such as
bni culverts, and other drainage struck, tests with your communi We may req uest that your community submit a descniption
and scliedule of maintenance activities necessary to enure this requirement,
We bad this dete mi nation on the twP=cnt- annual -chanc c flood. discharges com puted in the FIS f or your co mmunity with
considering subsequent ohanges M' watershed characteristics that could increase flood discharges. Future development of projects
up t am could cause increased flood discharges, which could Gauze incr sed flood ha &. A comprehensive restudy of your
comitxnity's flood hazard; would consider the cumulative e# cts of developm on flood discharges subsequent to the publication of
e FIS repot for your c mrnnnity and mould, therefore, establish gmter` flood ba rds in. this area.
"Four community must regulate all proposed fCoodplain development and ensurc that its rewired by Federal and/or Stato law have
hcen obtaincd. State or community of5ciai_s, ham on kn ow ledge of local conditions and in the interest of safct , n%ay set higher
stands s for construction or may I t development in floodpl.ain areas, if your Statc or oommuniry has adopted more restrictive or
comprehen floodplain managcincnt criteria, those cn' feria take precedence over the nn NFIP requirements.
We will not print and distn - byte this LOMR to primary users, such as local i�uran agents or mortgage lenders, i the cornmunity
,ll sme as a repository for the new data, we onooumge you to disseminate the information in this LONM by preparing a. newa release
for publication in your community's newspaper that describes the revision and cxplauks how your community will provide the data and
help interpret the NFIP maps. In that way, inte rested ponons, such as property owners,. insu=cc agents, and Mortga l can
benefit f m the information.
Thl determination it bad an the 00cd data presently avaUble. The enctov*�d documents provide aid tioral Informalion Mgarding this delermInatlon. If you have
any gwstlons about this docu +ery#, pleaue ccntact the FEMA leap Assistance Center tQ11 Et 1- 877 - 336-2627 (1477 -FEMA MAP) or by Wier iaddnnra i to the
MR Depot 3601 l Khmer Avenue, Atexandria, VIA 22304-. Additloml lnforrnstion about tha NFIP is avallabte on cur vm bsite at ht1p: /1wwwSerna.9 *v1nflp,
Joshua A. Sm Ith CFM, WDgram SP66allst
Engineering Management Branch
Mtlgaioa Dlrectorate 1 1255310.3.1,07" 220a 102-
Page 3 of 4 I Issue D aft. H A R 9 A n n I Effective Date: A P P 9 A WMA I C ase NO.* 07 ILOMR -APP
y oE
T
µ Federal Emergency Management Agency
Washington, D.C. 20472
0
LETTER OF MAP REVISION
DETERMINATION DOCUMENT (CONTINUED)
W e have desigaate4 a Consul Cpordination Officer (C O) to assist your community, Tile CCO will he the p mart' Hasson between
your comma ty and �I�.. For radon regarding your CO please con�t,
Mr. F Pagano
Director, Mitigatim Division
lFederal Fr ergency M anagcmcnt A pnoy, P eglon VI
Federal Re Ceti P oQm 206
800 North Lapp 2
Dentor� TX 76209
(940) 898
STATUS OF THE CO CITY NFTP NITA
We arc pro cessing a revised FIRM and FIS repoxt fQr Dallas County in our co unWwide fort; th erefov -', we will not phy sica lly revisc and
republish the FIRM an FIS art f y our community to incorporate the modifications made by this LOMB at s tf e,, P reliminary
co las of the countywide FRW and FIS report, urhic pm sent iaformatlen from th effective FI1Ms and FT imports fo y our community,
were �ubrnitted to your m=u=sty f or rtvlew on J une 22, 2007, We Nvi i€ orporate the modifications ma by this LOMR into the,
k punt vide FIRM and FIS report before they become effective.
This determhalion is based on ffie d data presently avaltable. The andMed dC4U Gnu PMvIde addltlonal (nf Qrmation ragatdmg this, dctatm)na to . It pu h we
any quastsonz -about this dowment, p1e�se conta& the F EMA Map Assislanoe Center tdl free at 1 --877- 336-262 (1- 877 -r- E A MAP) or by t tter addnnsed to the
OM R Depot, 3601 Elsenhomr Avenue, Alexan a, VA 22304.. AddItional InformOti Dn ebOUI the NF 1 P is avalkabl a on Qur we��1te at h11p.%1Awm.(ema.gav gyp.
Jos A. mKh CFI P rogram Speciallst
E ng irmefing Management Sraoc;h
Wgatlan aEmTAorate 1'12553 10,3.1 ,07062.203 102 - C
----------------------------
Page 4 of 4
I Datol MAR 2 4 2008
Effecti D e. APR - 2008 ----
Case No.t 0746-2203P LOMR -APP
A l £ -
4 Federal Emergency Managemen Ag
�. Washingt t on, D . . 20472
LE ER OF MAP R EVISI ON
D ETERMINATION DOCUMENT (CONTINUED)
P UBLIC NOTIFIC OF REVISION
PUBLIC NOTIFICATION
FLOODING SOURCE LOCATION OF R rz;FERENCED ELEVATION
SFE (FEET NGVD 29)
I MAPPANEL
EFFECTTW
REVISED
NUMBER(S)
Grail -evfne Creek AppMxiMiatafy 300 fart demnstroam of
485
484
4811 3C01 551
Denton Ta p Roa
proximatety 3W tact downstream of
502
501
1
St LeuEs Southvmstern Ralhwy
T ributary -1 of 13rapevkne Qreek JU81 up-straam of the conflueme nth Grapevine Creek
494
493
48113 CO 155 J
Wi 90 days of the szecovd pub lication in. the focal news paper, a citizen ma y regvest that w reconsid this determination. Any req uest
fo reconsideration must bc bascd can scientific or te chrdcal data. This revision b ecome effective 3 0 days fr om the date of this l etter.
Riowcvcr untl the 90 -day period hay elapse the revised WIFE% pr=ntod in this LONIR ma be changed*
A notice of changes l'U be p u blish e d its the F e d era l RegWcr. A sh ort notice a Will l pu blished i n yo lava nc� pa r on. or about
the dates l iste d b e l o w . Pi i refer to F MA r- bsi at https oodm fem � f�tg /bfe ' main. .nsp• for a m d etailed
1
d �ptton of propo B E chan which will p osted wit a w ee k of the date of the ener.
LOCAL l E SPAIPER Name: cqppell G azeire
tt,s-: 04/02)2008 04/09/2008
WOO -- - - --
l determInaflan is basted on ther flood data p� #[y avaVa 4 . Q endosi� d provide add taformation rag ing this dietermInatlon, If you have
Bny quesUons about this d ume nt, O se contact ft FEMA Map A nce C ` rT er toll free at i - 877- 336 -2827 (1.8`7 -FE1 MAR") Qr by ter adds'` =ad to the
' .DMK Depot, .�01 k;i nrKY r AWWO, A18X9ndria. VA M5U4. Pxlditl IntarmStion 000Lrt Ma Nh IV 1S :aVagari On OUT ri+e!bSlta at p.11WWW,101'1'la.S0 Jr1J$P,-
Joshua X Smith, CFM, Pwgram SperJafi
Eriglneed Management f3rarch
M ki aUon +Dim =rate 1 1 2553 10.3.1.07062203 1 02 -1 - A- C;
DUARTMENT OF HOMELAND SECURITY
FEDE EMERGENCY MANAGEMENT AGENCY
Proposed Base Flood. Elevation Determination for the City of Capp ell, Dallas
County, TX and Case No. 07-06-2203P&* The Department of Homeland eeLM' ty'
Federal Emergency Management Agency solicits technical information or comments on
the proposed Base -percent-annual-chance) - chance) Flood. Elevations (BFEs) shown in the
Flood Insurance Study (FIS) and/or r n the Flood Ins rail ce Rate Map (FTRN4) for your
community. These proposed B Es are the basis for the odp a t'n management measures
that your community 'is required to either adopt or show evi den ce of having in effect ill
order to qvalify or remain qualified for participation in the National Flood Insurance
Program (NFIP). For a detailed listing of the proposed :BFEs and Wormatim on the
statutory period provided for appeals, please visit FEM.' s Nvehsite at
litt s- / /\ VW , lflood a s.fem,a=gov /A /Scn'ptsibfe main.as , or caH the HMA Map
.ssista ce Center toll free at -S? -FEM MA
FE MA.- Rat ;e Flood Eleva o cep on th We
Wage I of 2
Home Vie o os i � Add otica � ��1 itf ��t�t� ������ Ad min "s#ratio n Logout
DEPARTMENT OF HOMELAND SECURITY
Federal Emergency Management Agency
pages to Base Flood Elevations Determinations
Po Table ------
E CG'+ Federal Emergency Management Agency (FEMA), Department of Homeland Security.
SUMM On August 23, 2001 the Department of Homeland S ecurity's Federal Emergency
Managernient Agency identified Special Flood Hazard Areas FH s), in the City. of Coppell, Callas
County, Texas, through issuance of a Flood Insuran Rate 'flap Fl M). The Mltigati06 Directorate
has determined that mod of the Base (1- par rot- abnuakchance) -Flood Elevatichs FEs) for
certain locations i this community is appro priate,
DATE$: Upon the second publication of notice of these changes in a newspaper of1ocal circulation
in your community, any person has 9 days in w hich he o r she c a n r through the Chief
Executive Officer of the comm unity, that the Mitigation Directorate - reconsider the det r inati bn. Any
request for reconsideration must be based on knowledge of changed conditions or new scientific or
technical data. All interested parties are on notice that until the 0 - day period elapses, the MAigation
Directorate's determination to modify the SFEs may itself be charged.
ADDRESSES Any person having knowledge o w ishing to comment on these changes should
i m m ediately notify:
The Honorable Douglas N. Stover
M ayor, City of Coppell
P.O. Box 9478
eppell, TX 75019
FOR FURTHER INFORMATION CONTACT: William R. Blanton, Jr., C FM, Chief, Engineerin
Management Branch, Mitigation Directorate, Federal E mergency Management Agency, 500
Street SW,, Washington, DC 20472, (202) 646-2903.
SUPPLEMENTARY INFORMATION: A hydraulic analysis was perfermQd to incorporate
modification to an existing bridge over Denton Tap load across Grapevine Creak and updated
topographic information along G rapevine Creek fr approximately 1 ,650 feet downstream of
Denton Tap Road to approximately 100 feet downstream of St, Louis So Railway and
along Tributary _-1 of G rape vi ne Creek from it's confluence with Grapevine Creek to app
800 feet upstream. It results in increases and decreases in BFHA and floodw wi dth for Grapevine
Creep and has resulted in decreased BF Es for both flooding sources., The table below indicates
existing and modified BFEs for selected locations along the affected lengths of the flooding source
(s) ci ted above.
* Elevation in feet 1 )l
ate. // ,t1N W - RF, 10 06 \48 TEXAS \1 1 3 DALLAS CO UNTY" 07.06- 03P1 orTe� onf., 3120/2008
FED: Base Flood .Elevation Nonces on, the Web Paso 2 of
t Elevation in feet (NAVD)
# depth in feet above
graund
" Elevation in meters (MSL)
4
Source of
L a Long
Existing
Modified
Affected
Flooding
Coordi
BFE
BFE
Communitie
G C reek
City of C oppell
A pproximately 300 feet
32 "
�' � " �
dow nstream of Denton
n
96
` 161#
48
484
Ta Road
Appr 300 feet
32 0
57 ' 09 t ' / ,
downstream of St, Lou i
�
00'0
' 502
01
Southwestern Railway
Tributary -1 of Grapevine Creep
City of Coppell
Just upstream of the
� �
7� „
� � �l � 1 -
c with
966
� 4
*4 93
Grapevine Creek
All elevations referenced to the National Geodetic Vertical Datum of 1929 (NGVD).
I National Geodetic Vertical Datum, rounded to nearest whole foot
North American 'vertical Datum, rounded to nearest whole foot
3 0epth in feet above ground, rounded to nearest whole foot
4 Men Sea Level, rounded to the nearest 0.1 meter
The charges are being made pursuant to Section 206 of the Flood Disaster Protection Act of 1973
(Public Lair 9 -234) and are in accordance with the National Flood Insurance Act of 1968, as
amended (Title X111 of the Housing and Urban Development Act of 1968, Public Law 90-448), 4
U. . � 4001 -4128, and 44 CFR Pa 65.
Under the above - m entioned Acts of 1 968 and 19 73, the Mitigation Di re mu st develop criteria
for floodplain management. To participate in the National Flood Insurance Program (NFIP), the
commumty must use the modified BFEs to administer the floodplain management treasures of the
N F l lam. These modifi FEs i ll als a used to calcul the a ppropriate flood insurance prem i u
rates for new buildings and their contents and for the second layer of insurance on existing buildings
and contents.
,f Updated{ Thursday, March 20 2008t
FEMA 500 C Street, SW Washi ngton, D, C. 20472 Phone: (20 2) 566 -1600
fiZe / /R. i�' tW -RE T.lO 1 06 \4 TFXAS\l 13 DALLAS COT-i 06- 2203P1 4) ospond,4 r 3120/2008
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Appendix C
Alexander Court Survey
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Appendix D
Smaller Scale of Alexander Court Survey with Focus on Lots 11 and 12
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Appendix E
HEC -RAS Output
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"Fence" run n value (as a sensitivity analysis) = 0.09
HEC -RAS River: RIVER -1 Reach: Reach -1
Reach
River Sta Profile
Plan
Q Total
Min Ch El
W.S. Elev
(cfs)
(ft)
(ft)
Reach -1
27555
Bridge
Reach -1
27540 Natural
MEffFW
10500
475
492.31
Reach -1
27540 Natural
Fence
10500
475
492.31
Reach -1
27540 Encroached
MEffFW
10500
475
492.31
Reach -1
27540 Encroached
Fence
10500
475
492.31
Reach -1
27400 Natural
MEffFW
10500
476
492.8
Reach -1
27400 Natural
Fence
10500
476
492.8
Reach -1
27400 Encroached
MEffFW
10500
476
492.8
Reach -1
27400 Encroached
Fence
10500
476
492.8
Reach -1
27050 Natural
MEffFW
10500
474
490.23
Reach -1
27050 Natural
Fence
10500
474
490.23
Reach -1
27050 Encroached
MEffFW
10500
474
490.39
Reach -1
27050 Encroached
Fence
10500
474
490.4
Reach -1
26880 Natural
MEffFW
11900
474
489.82
Reach -1
26880 Natural
Fence
11900
474
489.83
Reach -1
26880 Encroached
MEffFW
11900
474
489.85
Reach -1
26880 Encroached
Fence
11900
474
489.86
Reach -1
26700 Natural
MEffFW
11900
474
488.26
Reach -1
26700 Natural
Fence
11900
474
488.29
Reach -1
26700 Encroached
MEffFW
11900
474
488.38
Reach -1
26700 Encroached
Fence
11900
474
488.41
Reach -1
26300 Natural
MEffFW
11900
470
487.57
Reach -1
26300 Natural
Fence
11900
470
487.58
Reach -1
26300 Encroached
MEffFW
11900
470
487.75
Reach -1
26300 Encroached
Fence
11900
470
487.75
Reach -1
26170 Natural
MEffFW
11900
472
487.33
Reach -1
26170 Natural
Fence
11900
472
487.32
Reach -1
26170 Encroached
MEffFW
11900
472
487.51
Reach -1
26170 Encroached
Fence
11900
472
487.5
Reach -1
25820 Natural
MEffFW
11800
470
487.28
Reach -1
25820 Natural
Fence
11800
470
487.28
Reach -1
25820 Encroached
MEffFW
11800
470
487.34
Reach -1
25820 Encroached
Fence
11800
470
487.33
Reach -1
25725 Natural
MEffFW
11800
472
486.42
Reach -1
25725 Natural
Fence
11800
472
486.42
Reach -1
25725 Encroached
MEffFW
11800
472
486.56
Reach -1
25725 Encroached
Fence
11800
472
486.56
Lots 11 and 12