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November 16, 1990
Mr. Steve Goram
Director of Public Works
City of Coppell
732 Deforest Road
Coppell, Texas 75019
Reference: Oakbend Addition
Drainage Channel
Dear Steve:
This letter is intended to address the current impasse
between the City of Coppell Engineering Staff and Centex
concerning the proposed open channel adjacent to Lot 52 in
the Oakbend Addition. I realize that the presence of this
channel in its proposed location is an unusual design,
however, the location is necessitated by unusual
circumstances.
As I am sure you are aware, the area in the western
portion of the property was originally intended to be
dedicated to the City as park land. Through the process of
final plat approval and reconsideration of the zoning by the
City Council, the configuration of this area was changed.
Council action stated that 8 additional lots would be added
in this area and that Centex would pave half of State Road
along the west property line all the way to Thweatt Road, a
distance of over 1400 feet. The c~~st for this construction
is over $175,000 for a road that does not even serve the
subdivision.
As a result of the reconfiguration of the lot layout at
the western portion of the property, an existing drainage
channel which traverses the property at the southwest corner
was incorporated into the revised plan. The plan envisioned
an open channel on two sides of Lot 52 with 3:1 to 4:1
grassed side slopes and a concrete pilot channel. This
channel drains areas to the west of the subdivision and has
a flow under ultimate development conditions on the upstream
watershed of .480 GFS. The design for this channel which was
submitted to the City for review includes a box culvert
crossing the channel to access Lot 52.
I realize that the channel configuration is unusual but
there are many reasons why it should be allowed. .,City staff
has requested that the drainage be put underground and on
the surface this appears to be a good solution. By putting
the drainage in a box culvert, maintenance costs are lowered
somewhat, the drainage is hidden from view and liability
1660 S. Stemmons Frwy., Suite 150 / Lewisville, Texas 75067 / 214-221-5556
Mr. Steve Goram
Page 2/3
exposure is lowered to some extent. But from our
standpoint, however, there are far more compelling reasons
for the allowance of an open channel. Those reasons are
presented in detail below.
To begin with, the nature of the land layout, in our
opinion, makes the channel aesthetically pleasing as the
natural landscaping, including native stands of Cedar Elm
and Post Oak, are preserved by the routing of the channel.
Placement of a box culvert would involve the loss of many of
these trees due to placement of fill. In addition, the lot
has a certain amount of isolation with the drainage channel
as a buffer to the adjacent lots. We have already had
several inquiries from potential homeowners concerning the
availability of this lot. The lot is oversized and allows
more yard space than typical.
From a maintenance standpoint, the channel is not a
major problem as it is readily accessible and has 3:1 and
4:1 slopes over a major portion of its length allowing easy
mowing and cleaning. As if this were not enough, we have
offered to place the maintenance of the channel as a
responsibility of the Homeowner's Association which absolves
the City of responsibility. In addition, the liability
issue is answered as the Association must maintain liability
insurance. To state that the Homeowner's Association will
someday go away is a defeatist attitude. There are many
examples in the City of viable, ongoing Associations.
From a technical standpoint, the channel has been
engineered to contain the 100 year flood under ultimate
watershed development conditions. In fact, I personnally
instructed the design engineer during the design process to
keep velocities in the channel under 6 FPS, well under the
allowable 8 FPS allowed in an earthen channel. Staff has
indicated that erosion appears to be a problem. This is not
a valid issue as the only significant erosion that has
occurred in the channel banks has been at two points of
concentration where storm sewer has not yet been installed.
Completion of the proposed storm sewer will alleviate these
two erosion points. Contrary to staff comments, the channel
is extremely stable. Observation of the channel after the
two recent heavy rains indicates that the bottom of the
channel has not eroded in the least bit and has
satisfactorily contained the runoff. Based on my experience
as a hydraulic engineer, the channel is extremely stable as
it exists today. However, in order to conform with City
standards, we will be installing a concrete pilot channel to
protect the bottom and sod to prot<<.;t the side slopes.
Mr. Steve Goram
Page 3/3
A close review of the City's subdivision ordinance
indicates that open channels are indeed allowed and specific"
design standards are enumerated. I submit that this channel
is no different than Cottonwood Creek running along the
south edge of the Oakbend Addition between lots currently
being developed or from many other examples all over the
Metroplex area. There is neither any precedent or valid
reason for denying this channel.
The final reason which precludes the installation of a
box culvert is an economic one. The cost of installation of
the box culvert for the full length of the channel exceeds
$150,000 based on current estimates. To ignore the economic
aspects of this issue means to ignore reality. This cost of
construction is not justified in order to allow for the
presence of just one lot. It is more likely that if the
channel is denied, that this lot would be abandoned at a
severe detriment to the remaining lots on the cul-de-sac.
We have attempted to create an attractive and pleasing
environment for the future homeowners in the Oakbend
subdivision and would prefer to keep it that way.
I appreciate the cooperation of the City Staff in the
extensive review which has been conducted on this issue. I
request immediate approval of the' design plans for this
project so that construction may continue in a timely manner
with no further delay.
Thank-you for your time. If there are any further
questions or comments, please call so that we may set up a
meeting to discuss this further.
Sincerely,
CENT~.X REAL ESTATE CORPORATION
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Derek E. Earle, P.E.
cc: Mr. Alan Ratliff, City Manager
Ms. Shohre Daneshmand, P.E., Acting City Engineer
Mr. Mike Daniel, P.E., Nathan D. Maier
Mr. Gabe Favre, P.E., Ginn, Inc.
DEE/s