Park West CC(1)-CS 900307The City With ^ BeautHul Futuro
March 7, 1990
P.O. Box 470
Coppell, Texns 75019
214-402-0022
Mr. Don Davis
Consulting Engineers
5506 Cockrell Hill Road
Dallas, Texas 75236
RE: Park West Commerce Center / Final Plat
(Subject: Floodplain Management Meeting on March 2, 1990)
Dear Mr. Davis:
As per your request, we held a meeting on March 2, 1990, at 10:00
a.m. with you, Pat Acker from Albert Halff Associates, Shohre
Daneshmand from our office and myself in attendance. You made the
following comments:
As of this date, there has not been any type of floodplain
study report submitted the City of Coppell for subject
development.
Your client may retain Albert Halff Associate to conduct a
hydraulic study on Grapevine Creek.
Your client is requesting that the
review continue, since the hydraulic
effort.
final platting and plan
study will be a ongoing
You indicated that the conditional letter of map revision
which had been issued back in August of 1987, should still be
in effect. The only changes are the future bridge widening on
Southwestern Blvd., the removal of proposed bridge crossing
formerly known as Gateway Blvd. and the relocation of the
railroad bridge
In addition, Mr. Acker made the following comments:
The conditional letter of map revision has been issued and is
still in effect (see attached copy).
This project has been grandfathered per the new Floodplain
Ordinance.
The actual channelization had started back in the 1970's and
later Albert Halff got involved to finalize the hydraulic
study and received the letter of belief (the conditional
letter) in 1987.
As part of the said hydraulic study, FEMA expressed concerns
over high velocities, indicating this is an unstable
condition.
The proposed drop structure in the vicinity of 1-635 has not
been built as proposed. ~EMA does not recognize the
channelization through this property.
Albert Halff Associate will be looking at some other
alternatives to replace the proposed drop structure, in order
to satisfy what FZMA had requested and to satisfy our local
Floodplain Management Ordinance.
Based on our discussion during this meeting and our further review
of your request, we have the following comments that need to be
addressed.
Due to the changes made on the plat since this project changed
o~rnership and name, the above referenced conditional letter
of map revision does not appear to be still valid.
~urthermore, this conditional letter was issued by ~EM~ with
the consideration that proposed drop structure~ would be
built, which is not the case. ~urthermore, Pat Acker did
receive a response from FEMA on what would have to be
submitted to have channel accepted.
Please submit a hydraulic study report on the above referenced
project for City's review and comment, which is obtained by
the City through engineering services of Mr. Ron Morrison with
Kimley-Uorn. There will be a direct charge review fee not to
exceed $1000.
Provide a schedule on ~cope of work indicating when the
anticipated completion date on the floodplain study.
In response .to your request-for.continuing with the final
platting of this property, I would like to state that it has
been and will be our intent to work with you as diligently as
we have. However, it is important that, as noted above, a
hydraulic study be submitted immediately for staff's review
and comment in preparing for the related City Council meeting.
Attached for your u~e and application is a floodplain
development permit. This is required for all new development
in the City of Coppell. This permit is required before the
approval of the final plat and a FEMA conditional letter is
required to receive a floodplain development permit. Of
course, you must be in compliance with the City of Coppell
Floodplain Management Ordinance before a final plat can be
recommended to be approved, unless other arrangements are made
with the City Council.
The City of Coppell staff is totally receptive to modifications and
changes in development, but we need to be cautious to continue to
assure the integrity of the National Flood Insurance Program
(FEMA's requirements) for the entire City of Coppell and that our
current more conservative floodplain management requirements are
adhered to providing that level of protection also.
We appreciate your continued cooperation in developing this
premiere and complex development.
If you have any questions, please call Shohre Daneshmand or myself
at 462-8495.
erely' n
~D/MSD/bD
xc:
Steve Goram, Director of Public Works
Taryon Bowman, Planning & Zoning Coordinator
Mike Tucker, Prentiss Properties
Pat Acker,~lbertH. Halff Associates, lnc.
DDAVIS2.MSD
'l?cdcr;;d ]Znncrs'cncv
~' :~2,-
14ayor of ~e City of Col)poll '"' ' ' ·
P.0. Box a'18
Dear Mayor Duggan:
This is in r~farance to a letter dated ~ay...29, 1986, and technzcal data
submitted by Mr. I.:d Powell, P.E., former City Engineer for th~ City of Coppell,
Texas. In his l~tter, which was forwarded to us by our Region VI office,
Mr. Powcll requested that the Federal Emergency blanagement Agency (FIz:~) issue
bridue com3truchios project along Grapeviue Creek between Coppell Road and
Interr~tatc Ilighway 635. tehis proposed project involves realignment of the
Grapevine Creek channel including construction of a grass-lined channel with
at Freeport Parkway. Technical data s~mittcd in supimrt of ~is request
included a report entitled "Conditional Letter of Map Revision llaquefl'h for
Graj)evine Cre~ in Cop]~ell, T~xas," prepared by Alu~rt 11. llalfE Associates,
Inc. This re]?0tt contained a description of methodologies used and hydraul:Lc
procas:~ ~is request were received by 14arch 18, 1987.
During the course of review, we were informed that the channel modification
bctwoen Coppel]. ](oad and Freeport Psrkway and the construction of the Freeport
Parkway bridge were completed. Mr. B. An;ttole Falagan of Alber~ H. Halff
Associah(zs, Inc., s~mithod hydraulic analyser.:, which reflected the completed
j~ortion of th~ /~roj~:ct and requested that ~'EI4A review these analyses and issue
Letter of Map Revision. In reviewing the analyses, we noted that excessive
elocities exist in the earthen chaunel between ~he downstream end of the
omplehed channel modifications and 'the ]~roeport'" Parkway bridge, which could
esult in severe erosion asd undercutting o~[ both the bridge structure and the
od.Lfied chaqnel durin(j flo~din(~ wants. FEMA will ~ot perform a revisJ, on at
h~s tzmc to the ef]:ect~.ve 1.1ood Insurance Study (FZS), Flood Boundary and
loodway I4ap (PiIFI4), and Flood Insurance Rate Mai2 (l"Ii~i) ~or the City of
Cop~ll to reflect the completed portion of ~e ~annel modification and
bridge construction project due to the unstable conditions created by the
partial].y completed project. Our regional office has been notified of the
:;tabi].ity problem with the completed portion of the project, and will be
contracting your community in an effort to resolve this problem.
Wa have reviewed the data s~mitted for the entire channel modification and"
bridge construction project, and have d(~t,.~rmined that '~e project as a whole
City of Coppell will be warranted. I]ase (100-yea~:) ]flood ~lleva'tious and
floodway boundaries for Grapevine Creek would be revised as depicted in the
~lEorementioned report. ]?lease note theft future revisions to the I.'~.S, FBFM,
and FIR2-I or restudies si the flood hazards ill this area could modify this de-
termi;~ation.
This determination is based on the 100-year flood discharges computed in the
effective FIS for the City of Coppell, and does not consider subsequent
changes in watershed characteristics that would tend to increase flood dis-
charges. The development of this project and other projects upstream could
result in increased flood discharges, which, in turn, could result in in-
creased ~00-year flood elevations. Future.restudies of your community's flood
hazards, whic]~ would take into accoun[: the cumulative effects of deve].opment
on flood dlscharg~':~, could es t;d)lish higher 100-year flood elevations in this
This conditional Letter of ~4ap Revision is based on minimum floodplain man-
City of Coppell is responsible for approving all proposed floodplain develop-
merits, including this request, and for assuring that necessary permits re-
quired by Feder.'ll or State 1;]w haw~ been received. State and community
officials, based on knowledge of local conditions and in tile interest of
safety, may set higher standards for construction or may limit development in
floodplain areas. If tile State of Texas or the City Of Coppell has adopted
more restrictive or comprehensive floodplain management criteria, the.,~e
It shou].d bo noted that Nation%al Flood Incurance Program regulation 44 CFR
60.-~(b) (7) requires communities to "assure that the flood carrying capacity
within the altered or relocated portion of any watercourse is maintained."
This provision is incorpor, ated into your community's existing floodplain
management regulations; consequently, upon completion of. the project, re-
sponsibility for maintenance of the modified channel will rest with your
Upon completion of the entire project as proposed, your community may request
a revision to the effective ~!IS,. ~BFM, and FIRM. Tg~e revision ro¢Iuest should
be submitted to our Region VI office and must include tho data listed below:
"As-built" plans of the channel modification and bridge construction
project, certified by a registered engineer.
A w]:itten description of the methodology used to determine hydrologic
and/or hydraulic parameters, if different from the effective FIlS and
superseded by more curreat aud. technically superior data a~d
asalyses. (FEMA approval should be obtained before deviating
from the effective ~?IS paramd~ers.)
b. Since only a portion of the existing profiles is being revised,
the upstream and downstream p~rtions of the revised profiles
should coincide wfth thc effe."ctive FIS profiles, i.e., hydraulic
calculations should be continued upstream and downstream of the
revised area until water-surface elevations coincide with those
in the effective' FTS. -~.~ .
Two floodway hydraulic backwater models. The first should be a
duplication of the original baselihe model used in the effective FIS.
This is required to ensure that the original data has been duplicated
correctly. The secosd mode], should incorporate the completed project
and include any other channe], modifications or encroachment that have
Occurred in the floodplain since the original floodway was delineated.
If, however, additional cross sections are used in the second model
to provide a more detailed analysis of the complete~ project and its
effects on flood hazards, an intermediate model incorporating the
additional cross sections should also be submitted. This model must
reflect floodplain conditions as they existed at the 'time that the
original floodway was delineated and, therefore, it is important that
any cross sections added to '~le original model describe those con-
ditions. In addition, any improvements to the original modeling
techniqu~ may be incorporated into this intermediate model. This
,lode]. will then become the new baseline model and will be used 'to
accurately measure the effects Of the completed project.
5~e methodology and parameters for the revised floodway should
be consistent with the effective FIS, i.e., equal conveyance
reduction to establish encroachment limits, unless changes as
specified in item 3a have been approved by FEMA.
Since only a portion of the floodway is being revised, it must
'tie into the effective FIS floodway by duplicating thc results
of the original baseline model at cross sections upstream and
downstream of the project.
~%e revised floodway must carry the waters of'the base (~00-
year) flood without increasing the water-surface elevations of
that flood by more ~%an 1.0 foot over the original baseline
model at any point. If additional cross sections have been
incorporated, then revised floodway elevations also may not
exceed base flood elevations calculated in the new baseTine
model by more than 1.0 foot. In all cases, the revised'f'lo6dway
elevations may not exceed revised base flood elevations by more
than 1.0 foot.
Delineation of the 100- and 500-year flood boundaries, the 100-year
floodway boundary, and the locations and alignment of cross section, s
and flow line used in the hydraulic model.
This informa}'ion should be ~:hown on a map of suitable scale and
topographic de£inition to provide re~.sonable accuracy.
Ail items should be labeled for easy cross-referencing to
hydraulic model and summary data.
Source data and engineering documentation for the previously mentioned
items, as well as a bibliographic list of other sources of information
used.
We have enclosed documents entit].ed Conditions and Criteria for ~4np Revisions
and Con,]itio~%?. and Criteria for l.~loodway._~}{_s_v..j._.'.;j~_ons, which further dec, tribe the
nature and extent o~ the material needed to sujpport a r~]uest to revise an
effective FIS, FBFM and FII~. Compliance with the criteria outlined in these
documents ~.11 expedite FEMA's review process, thus allowing the effective
PIS, FBF~4, and FIRbt for your community to be revised as appropriate, in a
Should you have any questions .regarding this ma~ter, please do not hesitate to
contact the Chief, Natu~-al and '/'ethnological Hazards Division of the Federal
Emergency 14anagement Agency in Denton, Texas, at (I~7) 89g-9~ 27 Or members of
our ]lead¢luarters staff, in Washington, D.C., at (202) 646-2754.
Sincerely,
/J~,~ ~. ~a'tt.icke
Chief, ]~isk Studies Division