FS8601-CS 860604ANDERSON ENGINEERS, INC.
LAND & WATER ENGINEERING
Sune 4, 1986
13740 M~dway Road · Suite 608
· Dallas Texas 75244 · 214900 9977
The Honorable Lou Dugon, Mayor
city of Coppell
PO Box 478
Coppell, Texas 75919
re: Floodplain Management Guidelines
Deor Sir:
The following recommendations and the accompanying draft resolution are
submitted to you for inclusion in a proposed City of Coppell, Floodplain
Management Guidelines document to regulate and control development within the
watersheds and streams of the City of Coppell. These are submitted in partial
fulfillment of our contract agreement with the City of Coppell of December 9,
1985. The sections whiah follow give a brief background of our initial study,
identify the purpose of the proposed "Guidelines," and make some broad
recommendations for o more inclusive "Watershed Management Program."
BACKGROUND & SCOPE
Our final report, the Denton Creek Floodplain Study of May 15, 1986, identified
some general problems which con occur in urbanizing watersheds, addressed
several questions and concerns raised during the study period, and emphasized
specific problems which are likely to occur within the study segment of Denton
Creek, The tools and techniques for identifying end evaluating these potential
stream problems are generally available and accepted. The purpose of the
Floodplain Management Guidelines will be to establish the framework of step-by-
step processes within which it is essential for the City to operate in order to
maintain the desired control over City stream corridors.
WATERSHED/STREAM MANAGEMENT
In addition to the management of the City's stream corridors, it is important to
match a comparable level of watershed management which will help to preserve
and/or protect the stream system as a whole. That is, the watershed is the
source of the water in the streams and, thus, controlling the source can often
solve at least half of the potential problems along the associated stream
corridor.
In Coppell, a full watershed and stream corridor management program would
require Jurisdictionai cooperation between politicoi boundaries. However, this
is not unprecedented; the Cities of Ailen, Dalios, Gariond, McKinney, Piano and
REGISTERED ALABAMA ARKANSAS COLORADO ILLINOIS LOUISIANA MISSOURI NEW MEXICO TEXAS
6/4/86 City of Coppell - Page 2
Richardson have all recently adopted a program called, "The Interjurisdictionol
Watershed Management Program - Rowlett Creek," with the coordination and help of
the North Central Texas Council of Governments. A copy of the Clty of Plano's
resolution adoptlng the Rowlett Creek management policies is attached for your
reference os Appendix 5.
Fortunately for the City of Coppell, a vehicle for organizing a cooperative
management program for the Denton Creek stream corridor is in place os a result
of the recently completed draft Environmental Impact Statement for the Trinity
River corridor prepared by the US Army Corps of Engineers. The revlew
coordination through the North Central Texas Council of Governments can eoslly
be the forum through which such o cooperative agreement could begln to take
place for Denton Creek, with NCTCOG helplng to provlde the needed leadership to
organize such an effort.
RECO~T4ENDED ENGINEERING CRITERIA
The accompanying articles ore proposed for inclusion in the City code and as o
City councll resolution (Appendix 1) to provide the basis for development of a
detailed "Guidelines" manual. The Engineering Crlterla ore adopted from Section
4.2, Recommendations, of the May report on Denton Creek, os presented here in
Appendix 2. The adoption of these proposed criteria ore felt to be critical to
the management of future development within the City of Coppe11's floodplains.
If you have any questions or need clarification or revision of any of the items
discussed and presented in this letter,
Respectfully Submitted,
ANDERSON ENGINEERS, INC.
Carl V. Anderson, PE
President
attachments:
Appendix 1 - City Council Resolution
Appendlx 2 - City of Coppell Engineering Criteria
Appendix 5 - City of Plano Watershed Management Resolution
APPENDIX 1
CITY OF COPPEI_L
CITY COUNCIL RESOLUTION
CITY OF COPPELL RESOLUTION
WHEREAS, there is a need to develop an overall watershed and stream corridor
management program within the designated floodplains of the City of Coppell,
including a need for a systematic approach to decisions on applications for
development within floodplains; and
WHEREAS, there is a concern on the part of the City that natural streams and
waters of the City be protected and enhanced to restore, protect or improve the
historic, scenic, recreational and wildlife habitat of, along, and within the
floodplains; and
WHEREAS, there is o concern on the part of the City that storm water be moved
naturally rather than relying on extensive and costly systems of channel
improvements, that development be permitted where it would not create other
flood problems and where acquisition of property is not required for historic,
scenic, recreational, or ecological reasons, that the City maintains its
eligibility in the Federal Flood Insurance Program by assuring protection
against loss of lives and property in the floodplain, that historic, scenic,
recreational, and ecologically valued areas in the floodplain be preserved where
possible, and that a reasonable amount of the floodplain be provided in public
ownership to meet the open space needs of the City; Now, Therefore,
BE IT RESOLVED BY THE CITY COUNCIL OF THE CITY OF COPPELL, TEXAS:
Section 1. That the City Council hereby adopts the attached Engineering
Criteria for Floodplain Management as interim administrative guidelines to be
applled to ali creeks in the City of Coppell, including those which do not have
an approved stream master plan.
Section 2. That the City Manager and Pork Board be and ore hereby instructed to
seek oll possible sources of revenue for acquisition of floodplain land for open
space and recreation use where warranted.
Section 3. That these criteria are to be reviewed periodically, with the first
report in six (6) months after passage of this resolution. That the periodic
review cover the effectiveness of the criteria based on experience and their
effect on floodplains, and further, that the City continue with related current
studies, specifically studies of streams as they may relate to the historic,
scenic, recreational and wildlife habitat of, along, and within their
floodplains in order to provide more precise standards and guidelines as well as
the refinement of exlsting City codes and criteria.
Section ~. That this resolution shall take effect immediately from and
after its passage in accordance with the provisions of the Charter of
the City of Coppell, and it is accordingly so resolved.
APPROVED BY CITY COUNCIL:
DATE
ATTEST DATE
APPENDIX 2
CITY OF COPPELL
ENGINEERING CRITERIA FOR
FLOODPLAIN MANAGEMENT
ENG~NE£RING CRITERIA FOR FLOODPLAIN ~ANAGE~ENT
CRITERIA APPLICABILITY
These criteria shall apply to all watercourses originating within or flowing
within, through or along the City limits of the City of Coppell for streams and
creeks having a watershed equal to or greater than 1~0 acres.
CRITERIA
Design discharges for evaluation of streams in floodplains in the City of
Coppell shall be based on two discharges at the design point:
A. The Low-Flow discharge; defined as the discharge having a 95~ probability
of being equaled or exceeded (the 1.~5-yr mean recurrence interval
discharge) in a given year as determined by historical data or regional
regression equations; and
B. The Base-Flood discharge; defined as the l~-yr mean recurrence interval
discharge (1~ probability of being equaled or exceeded) from a fully
developed watershed determined by hydrograph methods.
Alterations of the channel or adjacent floodplain shall not result in any
increase in water surface elevation, on site, upstream nor downstream of the
project site in the Base Flood discharge.
Alterations of the channel or adjacent floodplain shall not result in any
changes in the Low-Flow channel hydraulics upstream nor downstream of the
project site.
No alterations shall occur to the Low-Flow channel except as provided for in
an approved stream master plan.
Alterations of the channel or adjacent floodplain shall not result in
eroslve velocities on site, upstream or downstream of the project, except
velocity shall occur upstream or downstream of the project site.
Alterations of the floodplain shall occur only if it can be shown that equal
conveyance alterations con occur on both sides of the channel and that all
other criteria are met.
7. Application for alterations of the channel or adjacent floodplain shall
include:
A. Hydrologic and hydraulic analyses clearly defining existing conditions,
proposed conditions and impacts of the project, including work mops and
stream profiles upstream and downstream of the site for sufficient distances
to demonstrate a match to existing conditions for at least 3 consecutive
B. A site grading and drainage plan showing cut slopes,
site contours, returns to adjacent property contours,
inundation lines;
fill slopes, on-
and l~O-yr flood
C. A landscape plan;
D. An erosion control plan or narrative describing temporary and permanent
erosion controls; and
E. Other such materials os may be required to clearly deflne the project
location, scope, and intended use.
APPENDIX 3
CITY OF PLANO
WATERSHED MANAGEMENT RESOLUTION
RESOLUTION NO,
85-12-20(R)
A RESOLUTION OF THE CITY COUNCIL OF THE CITY OF PLANe, TEXAS,
ADOPTING POLICIES FOR MANAGEMENT OF THE ROWLETT CREEK WATERSHED.
WHEREAS, Rowlett Creek is i major tributary in the City of Piano, end Its
watershed Ifil Il rapidly developing; and
WHEREAS, a Joint study wes completed In I cooperative effort by the cities of
Plane, Garland, Dallas, Allen, McKInney, and Richardson, ell of which have jurisdiction
over a portion of Rowlett Creek; end
WHEREAS, the Joint study has produced eight policies for management of the
Rowlett Creek Wetershed in order to protect public health end safety; end
WHEREAS, each of the involved cities has been requested to adopt these eight
policies;
NOW, THEREFORE, BE IT RESOLVED BY THE CITY COUNCIL OF THE CITY
OF PLANe, TEXAS:
Section [. The City Council hereby adopts the following policies to govern future
development of the Rowlett Creek watershed:
1. BFE: lOO-~ear Floodolaln- Fully Developed Watershed Land Use.
The bede faecal elevation {BFEJ end floodplain used for design and planning
should be evaluated upon total stormwater discharge quantities that will, through
future urhenlzetlon` be generated from a fully developed watershed.
2. Allow No Rise in Base Flood Elevation
Reclamation of the floodplain should be permitted only If It can be demonstrated
that there will be no rise in the base flood elevation.
Velocity Control,.
Velocity controls should be established which specify maximum allowable flow
rates for specific channel, bed and bank treatments.
NO Alteration or ChannelJzatlnn of Rowlett Creek and its Ma!or Tributari~
(except where required for safety and public welfare). The dralnageway of
the creek and Its major tributaries should be left In · natural state to control
erosive velocities, prevent excessive downstream discharges and preserve
the natural effect of the stream.
5. Seek Public Owner~hio of Remainlna Floodolalq~
Any floodplain remaining after final reclamation should be deeded or dedicated
to the city to prevent further encroachment end assure proper drainage
maintenance.
6. Buffer Zone,_
Each city should require parallel streets, greenberts, etc. along the stream
corridor to assure access and to create buffer zones between the floodplain
RESOLUTION NO. 85-[2-20(R)
and development.
7. Linear Park.
Cooperation In development of a contiguous linear park along the Rowlett
Creek stream co,rider Ih<mid be actively pursued.
8. Pursue Dl~eu,slon af ~_~clfic Development Standar~l.
Further evaluation end dllcusslon of specific development standards such as
detention .pollcl~ and minimum floor slab elevations should be jointly pursued
to In~ure adequate water quality protection and flmxl water control.
Section II. This relolutlon shill become effective immediately upon Its passage.
DULY PASSED AND APPROVED this the 23rclde¥ of
Jack Harvard, MA YO R
ATTEST;
Ja~kie Blakely, CITY sEC REI:~
APPROVED AS TO FORM:
Gary F. Chatham, CITY ATT~NEY