Country Estates-CS 930714 CONSULTING ENGINEERS, INC. ,
CityDirect°rof Coppell°f Public Works ' /,~0 '
255 Parkway Boulevard ~,~C
Coppell, Texas 75019
Dear Steve:
Please accept the attached information as a request for a minor modification to an area storm sewer inlet
on Lot 2, Block B of the Country Estates Subdivision. This area inlet was installed to merely accept local
drainage from approximately 9,500 square feet, or less than even the minimum lot in this R-12
subdivision.
I
TI'ds area inlet is planned to be raised f.o accommodate fill in a rather deep area of Lot 13-2 and the home
builder is desiring the installation of a '~domed-grate" type inlet cover rather than open inlet that is felt to
be much less desirable. Understandably there could be an interest in assuring that area drainage is
accommodated in the unlikely event that a grate inlet becomes clogged. We offer the following multiple
factors to assure that this will not cause concern.
1. The size of the drainage area (with a Q of approximately 1.1) is very small. In
fact it is approximately the runoff of 2/3 the size of our smallest Country Estates
lot.
2. The domed nature of the specified inlet cover allows for ample drainage even in
the unlikely event that debris was to accumulate around the edges. This cover is
a standard design manufactured by Neenah for this purpose.
3. Running a worst case scenario, that presumes even 100% closure of this drain,
results in drainage going into a 12' curb inlet in the alley immediately adjoining
this lot. This alley inlet design capacity exceeds 18 cfs and it currently accepts
only 11.9 cfs. In other words, this entire lot could be filled to drain to the alley
and have no problem whatsoever and the alley inlet could still have about 30%
unused capacity. The !imib_,cl lot fill will be done to make an effort at preserving
as many trees as practical on this lot and provide for a gentler swale to the area
inlet.
The Lot B-2 minimum finished floor elevation is 505.80. The alley elevation
adjacent to the area inlet is 504.70. Again givel~ a worst case scenario presuming
100% closure of this area inlet, tl-.e finished floor is, at minimum, more than a fool
higher than the alley with good positive d~ainage lo the 503.57 invert of the 12'
alley Inlet.
Three NorthPark/8800 N. Central Expwy./Suile 300/Dallas, Texas 7S231/(214) 739.4741
Mr. Steve Goram
July 14,1993
Page 2
We therefore propose, as per the attached plan, to raise the area inlet approximately four feet from
current level, provide for a two foot diameter inlet, and use a domed standard grate cover. As you can
see from the engineering plans attached, all drainage functions work well within the City standards and
well within good engineering standards. All contingencies are covered.
Please provide us with acknowledgment and approval of this minor modification, as we and the home
builder are anxious to proceed with the consiruction.
Sincerely,
NATHAN D. MAIER
CONSULTING ENGINEERS, INC.
Peter Stal~
PS/crab
Atlachment ~
NEENAH
B-43~OoA
TURTLE BACK
GRATE AND FRAME
TO TOP OF
WALL
TING I ~L-'E~' - LID AND FRAME
I / TO CITY Tvdle-I.~k ~ .nd Frames
~, ALL REIN~RCEMENT IN
'"~'"~'~'"" - ! ~~ ~
DETAIL. ~ I1~ I&M ~ I ~ I~
COUNTRY ES'TATE~
· ' ' I DETAIL FOR
" ' ............... ; ............ AREA DRAIN
DRAINAGE CALCULATIONS
AREA ACRES C I100 T¢
NO.
~'1" 2.27 0.43 11.60 I0 ~ il.9
IA 0.78 0.45 11.60 10 4.1
2 0.54 0.45 11.60 10
~ 3 0.68 0.45 11.60 10 3.6
4 0.36 0.45 11.60 I0 1.9
_ 5 1.05 0.45 11.60 10 5.5
__ 6 0.83 0.45 11.60 10 4.3
__ 7 Z41 0.45 11.60 10 IZ6
_ 8 030 0.45 11.60 I0 1.6
_ ~'.5'A." ' 0.22 0.45 11.60 I0
14 O
J,C. THWEAT
13,
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