Coppell Trade-CS040726COPPELL
July 26, 2004
Dayton MacAtee, P.E.
MacAtee Engineering
6440 North Central Expy., Suite 414
Dallas, TX 75206
RE: 40.655 Acre Tract of Land north of Sandy Lake Rd./200' west of Freeport Pkwy.
Dear Mr. MacAtee:
This letter is written as a follow-up to our telephone conversation of July 23, 2004 and your letter
dated July 25, 2004 concerning a preliminary drainage analysis on the subject tract.
Currently, drainage enters this site along the west side approximately 1/3 of the distance up from
Sandy Lake Road. It then travels generally in an easterly to northeasterly direction discharging
from the site in the northeast comer. The discharge of the water from the site is not in a well-
defined stream, but in a generally low area.
Based on information provided to this office, at the time of development there will be a channel
constructed through the site on a grade of approximately 0.40%. This channel will end
approximately 250' south of the north property line and then transition back to the natural
condition. The transition should be complete approximately 25 to 50 feet south of the north
property line. There will also be some type of riprap placed near the north property line to
further reduce velocities. No detailed information on a proposed cross section of channel was
provided with the drainage analysis; however, based on information provided in the letter it is
my understanding that the existing velocity in the undefined channel is approximately 3.52 fps
and the flow leaving the site is approximately 0.95 feet deep. Once the upstream drainage basin
is developed, based on information in the drainage analysis, the velocity of discharge will be
approximately 3.2 fps and the discharge depth will be approximately 1.24 feet.
This drainage analysis was provided to the city in an attempt to have the city offer an opinion as
to whether or not the downstream property owner would need to have approval of the drainage
design prior to development of the site. Based on information provided, there would be no
reason to gain access to the downstream property for grading purposes and the velocity will not
be increased to a point where there will be erosive action on the downstream property.
Therefore, this drainage design concept would be allowed on this development with the
following stipulations:
A property owner's agreement must be submitted to the city clearly showing that the
maintenance responsibility for this channel will be the property owners. This includes any
mowing, silt removal, or correction of erosion along the channel.
Because no detailed information has been submitted at this time, the city reserves the right to
make normal engineering review comments when preliminary and final plans are submitted
for the future development. If during those plan submittals, it is obvious that the drainage
concept has changed, i.e., velocities are increasing at the discharge or the discharge point is
lower than the natural ground to the north which requires entering the downstream property
for grading purposes, then the City of Coppell will require that the downstream property
owner be contacted prior to approval of any construction plans.
The decision at this time to "not require approval of the downstream property owner" is based
solely on information provided in the preliminary drainage and discharge analysis dated July 25,
2004 and signed and sealed by Dayton C. MacAtee, P.E. of MacAtee Engineering.
If you should have any questions or need any additional information please feel free to contact
me at your convenience.
Sincerely,
Kenneth M. Griffin, . .
Director of Engineering/Public Works
Office 972/304-3686
Fax 972/304-7041