Coppell Greens 1-CS 980901//'-'~/~ The City With A Beautiful Future
k._..~/ /~__._~ P.O. 80x 478
x 478
Texas 75019
-0022
September 1, 1998
James A. Koch
Pacheco Koch Engineers, Inc.
9401 LBJ Freeway, Suite 300
Dallas, Texas 75243
RE: High Point Oaks / Lewisville
Dear Mr. Koch:
Thank you for providing me the set of construction plans for property immediately north of and
adjacent to the Coppell Greens Subdivision within the City of Coppell. My concern was the
grading of the property north of Coppell Greens and the impact of the drainage from that
property on the Coppell Greens Subdivision. You are correct in stating that the amount of water
coming to the site has not been changed as your construction plans and the Coppell Green
construction plans show it is approximately 200 els. However, the manner in which that water
gets to the property is a concern to the City of Coppell. The current contour plans on Sheet 8 of
your construction plans show that the water for the most part generally flows to the east and west
and comes to somewhat of a discharge point approximately 600 feet west of Denton Tap Road.
That is the general location of where a discharge point is shown on the Coppell Green
Subdivision plans to take a gentle flow of water and convey it through their subdivision
southward. My concern with the grading as proposed in your plan, is that the flow of the water
is being reshaped and now lots on the north side of Coppell Greens will be receiving water from
this regrading, when in fact the natural contours show the water going further west before going
south. Also, a large part of this drainage in its current state drains into a pond and then
discharges at a slower and more controlled rate to the south. With your regrading the pond is
being eliminated and shifted to the very north edge of the drainage basin. Then all water that
generally drains to the south is flowing with no real control over the discharge rate.
I am unsure what the current requirements are in Lewisville as to whether or not there will be
erosion control or silt fences or hydro mulch required on this regrading. There is a concern
about silt being conveyed to the south and deposited into the natural channels in the Coppell
Greens Subdivision. I know your Storm Water Pollution Prevention Plan shows a temporary
sediment basin but there is a caveat that says "if required". Who makes that determination?
It was my understanding in our conversations that as the property develops drainage will be
collected in storm drain systems and eventually discharged at a point to the south. Your letter
states that ultimately it will be approximately 6 fps. Because the development to the south is a
new concept with wide open spaces behind lots that convey drainage, I am somewhat concerned
that a concentrated flow from a discharge point of 6 fps could create some erosion problems. In
the final design the City of Coppell would appreciate consideration being given to energy
dissipaters or some other technique to substantially reduce the velocity coming out of a
concentrated discharge point.
In summary my concern with the drainage grading plan as proposed is:
1. It changes the way water discharges to the south so that water is discharged into the entire
north part of Coppell Greens as opposed to more of a central point approximately 600 feet west
of Denton Tap Road. ~
2. There is a concern about the conveyance of silt to the south.
3. There is a concern about the ultimate discharge velocities into the earthen channel.
Again, I appreciate your willingness to provide the City of Coppell a set of construction plans,
but the above items do cause me some concern. Additionally, it could be beneficial to contact
Bill Anderson of Dowdey Anderson and Assoc., the consultant for the subdivision to the south,
to further discuss the impact of this grading on their development. If I can provide any
information or if you have any questions please feel free to contact me.
Sincerely,
Kenneth M. Griffin, P.E.
Director of Engineering and Public Works
CC:
T.S. Ktunar P.E., City of Lewisville