Waters Edge P1-CS 930126 NATHAN D. MAIER
CONSUI'rlN~ £NGIN££R$. INC.
January 26, 1993
Mr. Ken Griffin, P.E.
city of coppell
255 Parkway Boulevard
Coppell, Texas '/.5019
Dear Mr. Griffin:
This letter is in response to your letter of inquiry dated January 22, 1993.
In order to address your concerns with regard to erosion control, we have amended our plan to call for seeding
of the entire swale with 800 square feet of sod at the end of the swale near the proposed 'y~ inlet.
You have correctly pointed out that the hydraulic grade line during the design flood is above the inlet throat
Therefore, during a 100-year storm, there will be a temporary backwater condition into the swale.
Although we agree that this is not an ideal situation, there are several mitigating factors in this case as follows:
1. There is not a good alternative.
2. This backwater will be contained within the bottom of the swale and WIll generally be less
than one foot in depth.
3. The water will not be on or adjacent to any platted lot.
4. Any backwater condition will be a very short term event. There is a drop structure in the lake
just downstream of this location. Therefore, immediately after the upstream lake's inflow
drops, the water causing the backwater is over the dam and gone.
5. This entire situation will be climinnted at the time the affected property is developed. At this
time, a permanent underground system will be installed.
Thank your for your consideration of this unusual situation. Enclosed nre twelve sets of revised drawings. If
these are acceptable, please stamp 8 of them. Wc will pick them up.
Tim is working on the maintenance issue. We understand that this requirement must be satisfied prior to the
approval of the plans.
Please call if you have any questions.
Michael Daniel, P.E., R.P.LS.
lvlD/cmh
Enclosure
Three NorthPark/8800 N. Central Expwy./Suite 300/Dallaa, Texam 75231/(214) 739-4741