ST9905-CS021219
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December 19,2002
TranSystems Corporation
Paul Padilla, P.E.
3010 LBJ Freeway, Suite 990
Dallas, TX 75234
RE: Bethel Road Project ST 99-05
Dear Mr. Padilla:
This letter is being written as a follow-up to our telephone conversation on December 11, 2002. On
December 10, 2002 City Council approved a variance to our Subdivision Rules and Regulations that will
allow the drainage system within Bethel Road that drains runoff from DFW Airport property to be designed
at a frequency less than the 100-year ultimate design. Based on information that you have previously
provided, it is my understanding that the system, as currently designed, will convey approximately a 25-year
ultimate developed frequency storm. However, if DFW Airport were to provide detention on their property
at some future date when they develop, our system would then convey the 100-year ultimate design storm.
With this letter I am providing a copy of the approved City Council agenda item and my backup material.
This letter will serve as your authorization to design the system that drains the runoff from DFW Airport
property to accommodate a 25-year ultimate developed frequency storm, as opposed to the 100-year ultimate
design required by our Subdivision Rules and Regulations.
We will have a meeting the first part of January to address other issues associated with this project. My goal
is still to complete the design and put the project out to bid in mid-2003.
If you should have any questions or need additional information please feel free to contact me, if not I will
be contacting you shortly to schedule the January meeting to discuss other issues.
S';;:>f.f{--
Kenneth M. Griffin, P .E.
Director of EngineeringlPublic Works
Office 972/304-3686
Fax 972/304-7041
cc: Jerry Hodge, Dir. ofPW, City of Grapevine
255 PARKWAY * p,O SOX 478 * COPPELL TX 75019 * TEL 972/462 0022 * FAX 972/304 3673
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DEPT: EagiDeerioglPublle Works
AGENDA REQUEST FORM
COPPELL
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DATE: December 10, 2001
ITEM #: 101E
ITEM CAPTION:
Consider approval of a variance to the Coppell Code of Ordinances Chapter 13, Appendix C Design Criteria and
Standards, Section II Storm Sewers and Drainage, paragraph B Engineering Design for the construction of Bethel
Road.
GOAL(S):
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APPROVED BY
CITY COUNCIL Motion to Approve
~ON...ABOVE DATE 7 t&,~
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Vote - 7-0
EXECUTIVE SUMMARY:
Approval of this item will allow the design of West Bethel Road, from the west city limits to Freeport Parkway, to
proceed so that we can get back on schedule to bid the project for construction in late 2003.
Staff recommends approval of the variance to Chapter 13 of the Code of Ordinances and will be available to
answer any questions at the Council meeting.
FINANCIAL COMMENTS:
DIlL REVIEW, ;1ft
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MEMORANDUM
FROM THE
DEPARTMENT OF ENGINEERING
RE:
Mayor and City Council
Kenneth M. Griffin, P.E., Dir. of Engineering/Public Works
December 10, 2002
Consider approval of a variance to Subdivision Ordinance No. 94-643 of the
Code of Ordinances of the City of CoppeIl Appendix C Design Criteria and
Standards, Section II Storm Sewers and Drainage, paragraph B Engineering
Design.
To:
From:
Date:
The referenced section of the Subdivision Ordinance states "The Engineering design shall
generally conform to the criteria set forth in the City of Coppell City-Wide Storm Water
Management Study and the City of Dallas Drainage Design Manual." The Drainage Design
Manual for the City of Dallas states "All drainage systems will be designed to accommodate the
flow from the 100-year frequency storm. . .". Designing for the 100-year fully developed storm
is a criteria that has been utilized in the City of Coppell since approximately 1990. There are
some drainage systems within the City of Coppell which are not designed on the 100-year storm.
Most notably, the drainage system along MacArthur Blvd. from Deforest Road south to Sandy
Lake Road is designed on a 5-year frequency storm.
Attached to this agenda item is a memo from myself to Jim Witt and Clay Phillips that goes into
great detail about our attempts to design the drainage system in West Bethel Road on a 100-year
design frequency. However, in designing systems for a 100-year frequency it is important to note
where you are discharging the collected water. In the case of West Bethel Road, if you were to
build a system to efficiently convey the 100-year design storm it would discharge water into the
small creek on the east side of Loch Lane then convey the water through the unimproved portion
of Grapevine Creek north of the Coppell Senior Citizens Center. This creek in turn meanders
adjacent to Old Coppell Estates, Big Cedar, Country Estates, Grand Cove, Creekview Addition,
etc. As Council may be aware, there have been several complaints of erosion in Grapevine Creek
adjacent to those subdivisions. To collect all of the water and discharge it into Grapevine Creek
on a IOO-year design is not the appropriate design for this drainage system. At best. that would
be an irresponsible design that could create additional drainage problems downstream.
There have been two drainage studies performed on this drainage basin, the first in 1999 and the
second in 2002. Both studies point to the need for detention on the DFW Airport property. The
airport property comprises 242-acres of the 464-acres of drainage basin that drains to the
tributary on the east side of Loch Lane. This is approximately 52% of the entire drainage basin.
As can be seen by the detailed memo, there have been numerous meetings and conversations
with representatives of DFW Airport; however, in the final analysis, I have been told that DFW
"CITY OF COPPELL ENGINEERING - E.XCELLE:'iCE BY DESIGN"
Airport at this time will not support detention on their property nor acknowledge the concept or
need for detention.
At this time, I have three options concerning the drainage associated with West Bethel Road:
l. Indefinitely Postpone the project;
2. Build an efficient system that collects the 100-year runoff and discharge it into the
unimproved section of Grapevine Creek. This means seven 10'x5' box culverts within
Bethel Road discharging into the small tributary on the north side of Bethel Road east of
Loch Lane; or
3. Design a system that will handle the 100-year storm water runoff before the airport property
develops.
It is my opinion that Option 3 is the correct decision in the design of the drainage system. Option
3 gives us a lOO-year ultimate storm drain system until such time as DFW Airport develops the
242-acres of their property that drains through the City of Coppell.
If they develop irresponsibly and discharge all their water into our system, then our drainage
system will still have the future capacity to convey a 25-year storm. If they do the correct thing
when they develop and design detention to detain the increase in runoff on their property, then
our system will continue to have a 100-year capacity in the future. There are no guarantees on
what the future holds on the development of the airport property or whether or not the airport will
do a responsible development on the property in terms of drainage.
To keep the Bethel Road project moving ahead, my recommendation is that the variance to the
Subdivision Ordinance be approved to allow the construction of a drainage system that conveys
the lOO-year runoff as it exists prior to development of the 242-acres of the airport property.
Staff will be available to answer questions at the Council meeting.
"CITY OF COPPELL ENGINEERING - EXCELLENCE BY DESIGN"
MEMORANDUM
FROM THE
DEPARTMENT OF ENGINEERING
To:
Jim Witt, City Manager
Clay Phillips, Deputy City Manager
Kenneth M. Griffin, P.E., Dir. of Engineering/Public Works
November 14, 2002
Bethel Road Project ST 99-05
From:
Date:
RE:
Since 1998, the City of Coppell has been evaluating drainage associated with West Bethel Road. In
1998 the City of Coppell hosted a meeting between the then property owners of the two large tracts
of land on the north side of Bethel Road to discuss the development of their property in regard to
drainage in Bethel Road. Those tracts of land are now referred to as the "Champion" and "Duke-
Weeks" tracts. The drainage basin for this portion of Bethel Road also includes approximately 240
acres of airport property discharging into Bethel Road at Royal Lane. In addition to that, the bulk
postal facility and the Minyards tract also discharge into Bethel Road. In total, there was
approximately 676 acres of land that discharged into Bethel Road near Coppell Road.
Realizing that drainage was going to be the overriding design consideration for the construction of
Bethel Road, a drainage study was commissioned by the City of Coppell called the "Southwest
Coppell Storm Water Management Master Plan". It was a joint venture between the City of
Coppell, NCH and Coppell Industrial NY. The study was prepared by Halff and Associates. The
study pointed to the fact that detention would be required on the land north of Bethel Road and on
the airport property. The detention on the airport property was crucial because of the short distance
from Royal Lane to Freeport Parkway and the fact that there was no available land in that section
for detention.
In 2001, the City of Coppell entered into a design contract with TranSystems Corporation for the
design of Bethel Road from the west city limits to Freeport Parkway. The design contract was
structured so that there would be additional drainage studies to complement the previous drainage
study. TranSystems' drainage study also pointed to the fact that detention would be required. By
this time, the property north of Bethel Road had already been developed by "Champion" and
"Duke- Weeks" and in both cases the City of Coppell required detention that would not allow the
discharge of any additional water from the site than what would normally discharge in an
undeveloped condition. Also, the water from the "Champion" and "Duke-Weeks" property was
conveyed in an easterly direction and discharged into Grapevine Creek north of Loch Lane, not
directly into Bethel Road.
"CITY OF COPPELL ENGINEERING - EXCELLENCE BY DESIGN"
Page I 0/4
The chaUene:e now is to desil!l1 a drainae:e system that will convev a tOO-vear stonn and at the
same time not create any downstream erosion problems in Grapevine Creek. TranSystems has
provided two drainage studies for the City of Coppell to accommodate the drainage along Bethel
Road. Both studies show that detention will be required on the airport property. The detention on
the airport property is needed to detain the increase in water runoff when the 242-acres of airport
property develops. The last design by TranSystems shows two detention ponds strategically located
on the airport property generally along the west side of Royal Lane.
The design of a drainage system to accommodate the developed runoff along Bethel Road is not an
overwhelming engineering feat. Simply put, to convey the drainage along Bethel Road, it is only a
matter of installing additional box culverts. Preliminary design estimates are that there would need
to be seven lO'x5' box culverts along Bethel Road to accommodate the 100-year ultimate
developed runoff. However. the real challene:e in this desil!l1 is to balance the conveyance of
water with the potential for downstream erosion in Grapevine Creek. As you may be aware,
we have had erosion along a portion of Big Cedar and Country Estates and there is evidence of
erosion in Hunterwood Park. To effectively collect all the ultimate developed stormwater in a
drainage system in Bethel Road Le., the construction of seven 10'x5' box culverts, and convey that
water to Coppell Road and discharge it into Grapevine Creek just north of the Senior Citizens
Center would not be the wisest approach to accommodate the drainage associated with Bethel
Road. That approach would very effectively and rapidly convey a large amount of water to an
earthen channel and in effect create the potential for additional downstream erosion problems.
The e:oal in this drainae:e desie:n is to detain the increased runoff difference between the
undeveloped airport land as it exists today and the future developed airport land Detention
on the airport property is a critical component of this design. To that end, I met ""1th
representatives of DFW Airport in July 2002 and presented them a copy of the revised draft
drainage report prepared by TranSystems. That report detailed the necessity for detention on the
airport property. I left a copy of the report for their review and asked them to respond to me
concerning the likelihood of a detention basin on airport property. I was even willing to accept a
letter from the airport stating that if at some point in the future they chose to develop then they
would construct detention at that time.
I have a legal opinion from Pete Smith that states that the City of Coppell cannot require the airport
to abide by our subdivision rules and regulations in regard to the development of their property.
Therefore, unless the airport decides to create detention, the City of Coppell cannot require
detention, even on the section of land that lies within the City of Coppell. However, representatives
of DFW Airport stated that they are bound by EP A and other environmental rules and regulations
the same as any municipality. They also have to obtain all permits and approvals prior to
development of their property.
It was my hope based on the meeting, that I would receive correspondence from DFW Airport
stating that they understood the drainage situation and they would be willing to construct detention
on their property at a future date if they decided to develop the 240-acres that drain into the City of
Coppel!. After numerous telephone calls, I was told in October 2002 that there would be no letter
forthcoming obligating DFW Airport for any future action.
"CITY OF COPPELL ENGINEERING. EXCELLENCE BV DESIGN"
Page 2 of ./
The situation we find ourselves in today is:
. 1) The airport will not allow us to construct detention on their property;
. 2) The airport will not commit to construct detention in the future; and
. 3) It is my professional opinion that it would not be wise to construct an efficient system to
discharge all the future water into Grapevine Creek knowing that there are downstream erosion
problems that exist today.
I contacted our consultant, TranSystems, and asked them to evaluate the drainage system that was
proposed with Bethel Road to determine what level of capacity we would have in the future if no
detention was constructed on the airport property. In essence, what I was asking is: if we build a
system today in anticipation of detention on the airport property in the future and the airport chose
not to construct detention, but instead chose to discharge all of their water into our "undersized"
drainage system what level of capacity would we have in our drainage system? The reply to that
question is that we would have a drainage system capable of conveying about a 25-year fully
developed storm. If the system only conveys approximately a 25-year stonn, then any larger event
that we have i.e., 50 or 100-year storm, creates the potential for street flooding along Bethel Road.
The City of Coppell Subdivision Ordinance requires that drainage systems be designed for a 100-
year fully developed stonn event. Without a detention basin, the drainage system cannot be
designed for a [OO-year storm without discharging a substantial amount of water into an
lmimproved section of Grapevine Creek. At this point, I find myself at a standstill on moving
ahead with this project. One the one side if I build an efficient system to convey all the water in the
future, I stand a very strong risk of creating erosion problems in Grapevine Creek. On the other
side, if I authorize the consultant to only design a system that will convey a 25-year stonn I run the
risk of having street flooding along Bethel Road in those rare storm events that exceed a 25-year
frequency.
It is mv recommendation that we desil!n a drainal!e system capable of convevinl! a 25-vear
ultimate developed storm and work with the airport at some future date when they chose to
develop the property in Coppell to try to obtain some type of detention on site. It's important
to note that our system will convey the 100-year storm as long as the airport property remains
undeveloped. Also, if the airport constructs detention in the future, our system will still convey the
IOO-year stonn. The only situation that reduces the capacity of our system would be if the airport
fully developed their property and released all the water without detention. With an undersized
system downstream, if and when the airport decides to develop, they will be in a predicament of
how to convey their water because our system would not be adequate to allow the release of all of
their water. So there is a possibility that they would be forced to have some type of onsite detention
just by virtue of the downstream system being undersized. To construct a system not in
confonnance with the Subdivision Rule and Regulations requires a variance from City Council.
Therefore, I will take an agenda item on December 10, 2002 to request a variance.
If you have any questions, please feel free to contact me.
"CITY OF COPPELL ENGINEERING - EXCELLENCE BY DESIGN"
Page 3 of4
Summary of Key Dates:
. February 4,1999 "Southwest Coppell Storm Water Management Master Plan" by Halff &
Associates.
Sponsored by: The City ofCoppell, NCH, & Coppell Industrial NY
. March 22, 1999 Legal opinion from Pete Smith that we cannot require DFW Airport to
install detention.
. April 13, 1999 Memo to Curtis Inglis, DFW Airport, providing summary of meeting
between Halff & Assoc., and Tracy Thompson, Doug Bryan & Mike Pyles
of DFW Airport and requesting clarification of drainage requirements on
airport property.
. May 11, 1999 Summary of reply from Curtis Inglis of DFW. Mr. Inglis spoke with
Kevin Cox and Gary Keane and Mr. Inglis stated that development of
airport property would be accomplished in responsible manner.
. February 13,2001 Entered into design contract with TranSystems Corporation for Bethel
Road and associated drainage.
. January 18, 2002 Received "Drainage Report Executive Summary" from TranSystems.
Report outlined necessity for detention on DFW Airport property.
. May 30, 2002 Received "Revised Draft Drainage Report for Regional Detention
Analysis / Bethel Road Improvements".
. July l8, 2002 Met with representatives ofDFW Airport and provided copy of "Revised
Draft Drainage Report for Regional Detention Analysis / Bethel Road
Improvements" for their review.
. October 11,2002 Was informed that representatives ofDFW Airport would not commit to
any detention now or in the future.
. October 14, 2002 Requested evaluation of drainage system in Bethel Road if no detention
was provided by DFW Airport when they developed and our system was
constructed today as if there was no increase in runoff from DFW.
. October 25,2002 Received letter from TranSystems that system would convey
approximately a 25-year storm with ultimate development without
detention.
"CITY OF COPPELL ENGINEERING. EXCELLENCE BY DESIG:"i"
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