Magnolia Park-CS080425 (4)Page 1 of 2
Ken Griffin - Re: Drainage Diversion /Magnolia Park
From: Ken Griffin
To: BThomp1114
Date: 4/251200811:07 AM
Subject: Re: Drainage Diversion /Magnolia Park
CC: Clay Phillips; Rhonda Adloo
Brian
About 40% of the area that is between the bank and Magnolia Park is designed to flow to Magnolia
Park. The other 60% drains to the TxDOT drainage system. This means that the drainage system in
Magnolia Park was not designed to accept all the water from that site. If the property owner desires to
reroute all his water to Magnolia Park he needs to comply with the following:
They would need to hire an engineer that specializes in hydraulics and hydrology to perform a detailed
analysis of the drainage basin and system that currently accepts water from the 40% of the area to
determine if the existing drainage system has the capacity to accept rerouted water from the remainder
of the property. The analysis should also evaluate the impacts of the rerouted water to ensure that
there are no adverse impacts to the existing system and that the existing inlets and the overall system
continues to function correctly. While the area in question is smaller than the area to the west, the real
problem is that the existing system, under the alley, was not sized to accept the additional area. The
system was sized to accept 11.04 cfs of water. The rerouted amount would increase that number to
about 26 cfs. Sometimes you are able to force more water through a pipe system by allowing the
upstream end to build additional head to increase the velocity in the pipe and thus allow the pipe to
carry more water. It could be difficult to more than double the amount of water in the existing drainage
system. Also, building additional head on the upstream end of the system means that the water would
need to be higher at the inlets. If the water is so high that the inlets do not accept water, then the
system ceases to function and could lead to some flooding.
Again, a detailed analysis of the existing system, with the rerouted water, would be needed to answer
these questions. Without the analysis, the city can not approve the rerouting of the water to the
Magnolia Park drainage system.
If you have other questions or need additional information, please contact me at your convenience.
Ken Griffin, P. E.
Director of Engineering & Public Works
972-304-3686
kgriffin@ci.coppell.tx.us
»> BThompl 114 <bthompl 114@aol.com> 4/25/200810:25 AM »>
We are not talking about the property to the westwe are talking about the property between our north entrance
and the bank on the corner of Denton Tap and 121 on the north side of Natches Trace to.
Bryan Thompson
14785 Preston Rd suite 1000
Dallas, Texas 75254
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Page 2 of 2
972-884-6127
800-424-3978
fax 972-888-1696
In a message dated 04/25/08 10:15:29 Central Daylight Time, kgriffin@ci.coppell.tx.us writes:
Brian
I have reviewed the drainage design for Magnolia Park and have the following observations to
offer:
1) The west side of Magnolia Park appears to be the high point in the drainage area. This
means that Magnolia Park's drainage flows east to the channel and the property to the west
drains west and south, away from Magnolia Park;
2) Neither the Magnolia Park channel nor the culverts beneath Waverly Lane or Levee Place
were designed to accept water from the west of Magnolia Park.
If the property to the west still desires to pursue discharging their drainage to the east and into
Magnolia Park, they would need to hire an engineer that specializes in hydraulics and
hydrology to perform a detailed analysis of the entire drainage basin and system to determine if
the existing drainage system and culverts have the capacity to accept rerouted water from the
west. The analysis should also evaluate the impacts of the rerouted water to ensure that
there are no adverse impacts to the existing houses that may lead to potential flooding in the
future.
Without the analysis, the only decision that the city can offer in this matter is that the water can
not be rerouted to the Magnolia Park drainage system.
If you have other questions or need additional information, please contact me at your
convenience.
Ken Griffin, P. E.
Director of Engineering & Public Works
972-304-3686
kgriffin@ci.coppell.tx.us
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