Creekview Add PD-AG 880112 Beautiful Future
' CITY COUNCIL AGENDA REQUEST
AGENDA DATE REQUESTED:
III. RECOMMENDATION OF PLANNING & ZONING COMMISSION:
STAFF RECOMMENDATION: Staff recommends approval.
IV. STAFF REPRESENTATIVE(S) TO ATTEND COUNCIL MEETING:
Kevin Peiffer, ~.~,n: Inc.
VI.
VII.
VIII.
IX.
X.
RECOMMMENDED TO BE DISCUSSED AT PRE-COUNCIL BRIEFING: Yes __ No __
SUPPORT MATERIAL: SUBMITTED Yes X No
DATE SUBMITTED TO CITY ATTORNEY'S OFFICE FOR PREPARATION OF ANY LEGAL
DOCUMENT, ORDINANCE, RESOLUTION, ETC.
FINANCIAL REVIEW:
BUDGETED ITEM
NON BUDGETED ITEM
ORIGINAL ESTIMATE OR BUDGET
CURRENT ESTIMATE:
AMOUNT UNDER OR OVER BUDGET
SUBMITTED BY
SOURCE OF FUNDING:
BOND FUNDS
OPERATING BUDGET
OTHER:
ACCT. NO.
Kevin Peiffer, G~-n= Inc.
APPROVAL OF CITY MANAGER'S OFFICE:
HOLD
AGNDARQSTFORM
MNITS
CITY MANAGER'S COMMENTS/RECOMMENDATION FOR AGENDA ITEM
I. Item #10
CITY COUNCIL AGENDA DATED: January 12, 1988
II. COMMENTS/RECOMMENDATION:
The project as presented does not meet the requirements of the
Floodplain Ordinance due to slight rises in water surface elevation and
increases in velocity within the project limits. The increases,
however, are very minor and do not adversely impact the existing
residences to the North, or their planned development. Adequate
freeboard still will exist for all properties adjacent to this project
and erosion protection has been provided through their dedication of the
floodway/floodplain easement. Therefore, staff recommends approval of
this variance as requested. (Article 5, Section D - Engineering
Criteria for Floodplain Management, paragraphs 3 and 6b on pages 36 and
37, respectively, of the Comprehensive Floodplain Ordinance)
#10/011288
MDEB
DALLAS
e
The written notice shall be filed for record in the county Deed of
Records and a copy of the notice must accompany the application for
d evelopm ent pe rmi:."
All structures ~laced in areas subject to shallow flooding (AO/AH
Zones) or in low areas where ponding of surface runoff or sheet-How
flooding may occur, shall have the lowest floor (including basement)
placed at the FIRM specified depth number (in feet if specified), or a
minimum of 2 feet above the highest adjacent grade, whichever is
higher. Where the direction of sheet How is towards a building, all
areas around the structure shall be sloped away from the structure and
the site graded to direct the flow around and away from the structure.
SECTION D. Engineering Criteria for Floodplain Management
In addition to the provisions of the general and specific standards of this
ordinance, the following engineering criteria shall apply to all
development within river'me or lacustrine floodplains of the City:
Design discharges for evaluation of riverine floodplains in the City of
Coppell shall be based on three discharges at the design point, and, in
the case of Hood' protection by levees, a fourth discharge shall be
included for design of the levees, as follows:
a. The "mean annual Hood;" defined for purposes of this ordinance as
:he discharge having a 50% probability of being equaled or exceeded
in a given year (approximately the 2-year mean recurrence interval)
as determined by historical data or regional regression equations
of the State Department of Highways and Public Transportation;
b. The design base Hood discharge; defined as the discharge having a
1% probability of being equaled or exceeded in a given year (the
100-year mean recurrence interval) from a fully developed
watershed. Discharges shall be determined by hydrograph methods
for areas larger th:~n 0.25 square miles, by either hydrograph
methods or rational formula methods for areas from 6 acres to 0.25
square miles and by the rational formula methods at locations
having less than 6 acres of contributing area.
Octoeer t, ~987 - a~e ~5
0
c. The iow-flow or base-flow discharge; defined as the dry weather
flow as determined by historical data or assumed to be no less than
5 csm in this ordinance.
d. The standard project flood; defined in this ordin-nce as the flood
which would occur in the event of a 50% PMF as determined by an
evaluation of the probable maximum precipitation as ouUined in
Hydrometeorological Reports 51, "Probable Maximum Precipitation
Estimates, United States East o[ the lOSth Meridian" and 52,
"Application o[ Probable Maximum Precipitation United States East
o[ the lOSth Meridian."
Alterations of the channel or adjacent floodplain shall not cause the
average channel velocities during the mean annual flood to exceed
maximum permissible velocities upstream or downstream of the project
site.
Alterations of the channel or adjaceat floodplain shall not result in
any increase in water surface elevation, on site, upstream nor
downstream of the project site in the fulIy developed watershed design
base flood discharge.
No alterations shall occur to the low-flow channel in park or green-
belt areas except as provided for in an approved master plan. If
structural pilot c--mnels are approved, the low-flow discharge shall be
fully contained within the pilot channel with 6 inches of freeboard.
Flood protection offered by proposed .levees shall be designed based on
the standard project flood plus three feet of freeboard.
Alterations of the channel or adjacent floodplain shall not result in
average desi~ base flood velocities which exceed the maximum
pe,missible velocities of this ordinance on site, upstrenm or
downstream of the project.
a. If off=site velocities in the natural channel are erosive, no
increase i.u velocity shall result at the upstream or downstream
erosive velocity location. No exceptions will be made for
increases in erosive off-site velocities except as approved by the
floodplain administrator.
Oc*.oi~er ~J, !98'/ - ~ge ~6
~W. OODI~I.~IN ,~A~'~ ~RIIINANCi:
~ b. Exceptions to this rule will be made for erosive velocities within
on-site channels for aesthetic or environmental considerations if
it can be show, n that such velocities are in the best aesthetic or
environmental interest, provided sufficient area is designated for
flcxxi-related erosion which will occur in the high velocity reach
and provided no structures will be adversely affected by such high
velocities.
o
Alterations of the floodplain shall occur only if it can be shown that
equal conveyance alterations can occur on both sides of the channel and
that all other provisions and criteria of this ordinance are met.
Design of lakes, ponds, stock tanks, detention, or detention/retention
facilities shall be based on the discharges and other requirements of
the Texas Water Commission.
Permit applications shall be made to the Floodplain Administrator as
outlined in Section C, Article 4, for alterations of the chsrmel or
adjacent floodplain and shall include, as a minimum:
a. Hydrologic and hydraulic analyses clearly defining existing
conditions, proposed conditions and impacts of the project,
including work maps and stresm profiles upstre-m and downstream of
the site for sufficient distances to demonstrate a match to
existing conditions for at least 3 consecutive cross-sections.
b. A site grading and drainage plan showing proposed cut slopes, fill
slopes, on-site contours, returns to adjacent property contours,
existing contours, and the existing and proposed 100-year flood
inundation lines.
c. The site plans shall include a delineation of landscaped areas
showing the general type and extent of landscape materials proposed
to remain or be placed within the floodplain.
d. A narrative or plan shall be provided which depicts temporary and
permanent erosion controls to protect disturbed and post-
development floodplain overbank or channel areas:
Octoeer 8. 1987 - ?~e ~?
GINN, INC.
CONSULTING ENGINEERS
TO:
FROM:
Shohre Daneshmand
Kevin Peiffe~P
DATE:
December 29, 1987
SUBJECT: Creekview Addition - Variance Request
We have reviewed the above referenced subject and related
correspondence (attached) with Mr. Carl Anderson for conformance
to the City's Floodplain Ordinance.
We recommend approval of this variance request based on review
of the engineering data submitted by NDM Consulting Engineers on
12/18/87 and 12/21/87 and the comments provided by Mr. Carl
Anderson on 12/23/87 (copy attached).
Please place this item on the January 12, 1988 City Council
agenda per their request.
We will be available at the 1/12/88 council meeting to answer any
questions that the Council may have regarding this issue. Also,
please enclose a copy of this recommendation in the council
packets.
Thank you and please call if you should have any questions.
cc:
Alan D. Ratliff
Dennis Johnson
Wayne Ginn
Taryon Bowman
Carl Anderson
17103 Preston Road · Suite 100 · LB 118 · Dallas, Texas 75248 · Phone 214/248-4900
FILE COPY
Kimley. Horn and As ciates, Inc. 12660 Colt Road, Suite 200, Dallas, Texas 75251 · (214) 386-7007
Raleigh, Durham, Charlotte, Nashville, Virginia Beach, Washington, Dallas,
December 23, 1987 West Palm Beach, Tampa, Orlando, FL Lauderdale, Veto Beach, Ft. Myers, Phoenix/
Mr. Kevin Peiffer
Ginn, Inc.
17103 Preston Road - Suite 100
Lock Box 118
Dallas, Texas 75248
re: Creek View Addition - Floodplain Study
Grapevine Creek - Coppell, Texas
Dear Mr. Peiffer:
We have completed a review of the submittals by Nathan D. Maier Consulting
Engineers, Inc. (NDM) on the above project. Submittals reviewed include
data from HEC-2 computer models of 12/18 and 12/21/87 as well as their
earlier models. As you requested, these reviews have been made in light of
their petition of 12/18/87 for a variance to the new City of Coppell
Floodplain Management Ordinance.
To summarize our reviews, the project as proposed will have little effect
on the Grapevine Creek floodplain. That is, the impacts on the effective
flood insurance study (FIS)base flood are nil; the impacts on the ultimate
conditions 2-yr flood event are nil; and, although they are evident, the
impacts on the ultimate conditions base flood (the design base flood) are
felt to be minimal and within acceptable limits.
Design base-flood velocities increase at four locations, in areas already
having erosive velocities, but in reaches having large floodplain limits to
accommodate erosion and meandering which may result from those future
velocity increases. Other design base-flood velocity increases are less
than 0.1 fps in locations of non-erosive velocities, assuming 8 fps is the
erosion threshold velocity. Further, the design base-flood water surface
elevations increase from less than 0.1 ft to less than 0.3 ft at seven
Building client relationships since 1967
December 23, 1987 - Page 2
Mr. Kevin Peiffer
locations within the Creek View study reach of Grapevine Creek. The
increases in design base-flood elevation are at locations with existing
home finish floor elevations two feet or more above the calculated water
surface elevation.
It is our feeling that NDM has done all that is reasonably possible in
order to meet the conditions of the new ordinance while attempting to meet
the desires of nearby homeowners to minimize environmental/aesthetic
impacts and still make the project economically feasible. For these
reasons we recommend staff approval of the proposed variance request for
the Creek View project, as presented by NDM in their computer models which
include data of 12/21/87, with the following provisions:
1. That the floodplain/floodway limits shown in the drawings be
considered as acceptable regions of possible erosion or stream
meandering in the erosive velocity reaches;
2. That the finish floor elevations of all existing homes in the Creek
View reach of Grapevine Creek are above the design base-flood
elevations, as would occur with the proposed development of Creek
View, by an amount equal to or greater than elevations otherwise
stipulated in the new Floodplain Management Ordinance; and
3. That all other provisions of the Floodplain Mana~,ernent Ordinance
are met.
If you need further information or have any questions before the City
Council meeting to address the variance request, please call.
Sincerely,
KIMLEY-HORN & ASSOCIATES, INC.
Carl ¥. Anderson, PE
Senior Hydrologist
NATHAN D. MAIER
CONSULTING ENGINEERS, INC.
December 18, 1987
FILE COPY
Hr. Kevin Pieffer
Ginn, Incorporated
17103 Preston Road
Suite 100, LB 118
Dallas, TX 75248
Re: Creekview Variance
NDH No.: 87-6-062
Dear Mr. Peiffer:
Pursuant to our meetinS of December 14, 1987, we provide you, the City
of Coppe11 and Hr. Carl Anderson, with this request for a ~to the new
floodplain ordinance for the Creekview project. Wa would like to be included
on the agenda for the ~anuar~ 12, 1988 co_tmail
Additional changes have been~ade to the plans and we have again chan~ed
the hydraulic ~odels to reflect additional compro~ise from those plans
previously submitted. F~om our December 7, 1987 letter, while not our
preference, we have incorporated cbaml9lization of the overbank along the west
end of the p~roJect and actually reduced the lO0oyear ultimate water surface
upstream [rom the site. Basic than§es that were made to the December 7, 1987
hydraulic model, include widening the floodplain at sections 1.0, 22600, 3.0,
and 4.0, a distance of 20' 10', 10', and 10', respectively by moving the fill
limit line back farther f~om the Creek, chan~ed the fill boundary to a 3.:1
sloped encroaclu~ent rather than a vertical encroaclu~ent, and. l~we~in~.
right overbank 'n' value to account for underbrush cl~arin~, on
several of the lots. Tabulations of water surface elevations aaa velocities
are enclosed for your review.
At this point, we have taken all reasonable measures to co~ply with the
present ordinance. The fill licit boundary on ~ost of the lots fronting the
Creek has been reduced to a "bare mini~um", and will certainlys li~it the
~ accep_tao Is. ~,~
Three NorthPark/8800 N. Central Expw¥./Suite 300/Dallas, Texao 75231/(214) 739-4741
Mr. Kevin Pieffer
December 18, 1987
Page 2
Working with you, John Kahrlsruher, Carl Anderson and Shohre Daneshmand,
we have together provided for some very si~nificant improvements to the
previous models. These include:
1. Lowering water levels and velocities in certain parts of the study
reach up to 0.21 feet. Water levels increase up to 0.27 feet with
this project in certain areas, however, no existing structures will
be flooded. The maximum water surface increase with the enclosed
hydraulic model has been reduced from 0.42 (12/7/87 model) to 0.27
feet. Slmilarily, the maximum channel velocity increase has been
reduced from 0.82 to 0.56 feet per second. The velocity increases
generally occur at straight sections of the Creek (e.g. sections
1.0, 22600 and 4.0). The north overbank velocities along the toe of
slope of the existing homes, is generally 2.05 to 4.31 feet per
second, which is not erosive and should not threaten existing
structures.
2. Actually reducing ultimate 100-year flood waters upstream from
Denton Top Road by up to 0.20 feet.
3. The project will have no impact on the 2-year flood for ultimate
watershed build-out conditions.
Being in compliance with all FEMA re~ulations, and in compliance
with the City of Coppell ordinance in effect at the time the project
was conceived and largely designed.
Lots along the north side of Bethel Road will be filled by each home
builder and architect, only to the extent necessary to design a home. To this
end, maximum fill will not occur on most of the 26 lots alone Grapevine Creek,
especially since each owners motivation will be the preservation of the large
trees that presently occupy most' of this area. As you ara aware, the models,
however detailed, cannot account for these situations, and conditions will
surely be benefited by these accommodations. The fill limit boundary on each
of these lots has been revised to the absolute minimum without requiring
significant channelization of the Creek, loss of trees and vegetation, and
without requiring a major redesign of the already approved final plat.
Mr. Kevtn Pieffer
December 18, 1987
Page 3
We feel we have made every effort to achieve a workable solution, given
the status and timing of Creekvtew. The mitigating factors described above,
coupled with the fact that we are in compliance with federal (FEHA) criteria,
allows us to request your support of this request. Please feel £ree to call
should you have any questions regarding the new model or this request.
Sincerely,
NATHAN D. HALER
'LTING ENGINEERS, INC.
Dennis L. Johnson, P.E.
DI~/ld
cc: Carl Anderson
Shohre Daneshmand