DR0302-CS 910129IIz -1 I9r
J. Sandy Knoll Drive/Shadowcrest Lane Street Flooding
1. Statement of Problem
Complaints were logged from city files of street flooding and standing water at the intersection in this intersection on the
of Sandy Knoll Drive and Woodhurst Drive. Storm onstant ru noff a ntrance and front of the
south side, often curb deep. In addition, water Y stands
residence at 510 Shadowcrest Lane immediately eat of Sandy Knoll Drive. During storms this water is often
over the curb and is causing erosion to the p
2. Summary of Data
The study area is located in Willowood Subdivision and was designed in 1978. Drainage plans
for the subdivision were located in city archives �n ration a runoff t coefficien (C) of P 4� bField
rational method using a 15 minute time of con
reconnaissance of the study area was made on May 9, 1990, June 26, 1990 and October 19, 1990.
3 Analysis of Existing Conditions
Storm water runoff was analyzed using current city drainage criteria. A drainage area map
Lane is currently
was developed for the study area. The intersection n of S RCP Knoll two 10 foot curb The 36 inch RCP
drained by a 36 inch diameter reinforced concrete p p
flows east 775 feet along the centerline of Shadowcrest the 5 year flood but does not hay stream he capacity necessary
current design criteria the existing system will d 5-y
ear
handle 100 -year storm runoff. The alley be the a Sandy Knoll/Shadowcrest ntersection. inlet was
'Y' inlet located approximately 450 feet east
designed to intercept the off -site now from the Knoll alley which has no acces
uent the eY' pmnt
added a small amount of additional flow to the Sandy
contributes to the flooding problem at the alley intersection and Shadowcrest Lane. The street also appears
to have experienced significant differential settlement, which contributes to the standing water. Positive
overflow was originally to the east into Strea
Field inspection at the intersection of Sandy h a ng. oodhurst Drives revealed that this
area has also endured differential settlement creating P
4. Proposed Solution
The recommended solutions to solve the flooding in this study area include street and drainage
improvements as shown n red on Figure VII-10. e have been separated epar ted improvements
nto two stages. Stage I includes des the
and frequent flooding on Shadowcrest La
installation of one 10 foot inlet on each side of ne bo h t sides of the str exis
street would also be repllaced. C In
The pavement n front of 510 Shadowcrest La
ected
addition, the inlet lateral on the south side of the street nrStrea vide add rional pacify within the existing
d to the existing headwall with a 21 _inch R will P
system. The estimated probable cost of Stage I is $222,000. These improvements should remove the constantly
standing water and control the frequent street flooding.
The Stage II improvements consist of a 14 foot inlet connected to the existing inlet on the
west side of Sandy Knoll Drive and two 4 -foot grate inlets at the intersection of the alleys. The grate inlets
■
VII -26
will be connected to the existing 'Y' inlet diverting the additional offsite flow back into the existing 27 -inch
RCP. These improvements are estimated to cost $60,000 including removal and replacement of the alley
pavement. With the completion of Stage II the Sandy Knoll/Shadowcrest storm sewer system will have 25 -year
capacity with positive overflow in the street to Stream G6.
The standing water problem at the intersection of Sandy Knoll Drive and Woodhurst Drive
can be solved by removing and reconstructing 100 linear feet of pavement at the original design slope of 0.50
percent. The final design should include stabilization of the subgrade with lime or a similar subgrade
treatment method. The estimated cost of this improvement is $19,000.
The total estimated cost of all the recommended improvements in the Sandy Knoll
Drive / Shadowcrest Lane area is $101,000. It is recommended that the pavement repairs at the intersection
of Sandy Knoll and Woodhurst Drives and Shadowcrest - Stage I be performed concurrently for a total cost
of $41,000. The Shadowcrest Lane area could then be monitored on a regular basis and Stage II scheduled
as funds become available.
K. Parkwood Channel
Parkwood Channel is a .85 mile long tributary of Denton Creek which flows in a northerly direction
from a point approximately 700 feet upstream of Moore Road to its confluence with Denton Creek, just
downstream of a small lake (See Figure VII -11). The City of Coppell has received complaints regarding
erosion problems in the reach of the channel downstream of Parkway Boulevard. The hydraulic analysis
revealed potentially erosive velocities in this area (6 -9 fps), especially in light of the sandy soils prevalent along
the channel. The recommended design solution for this problem involves lining the existing side slopes for
2000 feet from the lake to the existing lined channel downstream of Parkway Boulevard. The slope would be
lined from the existing concrete pilot channel up to an elevation one foot above the fully developed 100 year
flood elevation. This solution would not only provide the desired erosion protection but would also greatly
reduce the maintenance which the City is currently required to perform. The estimated probable cost for these
improvements is $405,000.
VII -27
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ITV ALL 2 -4' GRATE INLETS
INSTALL 410 L.F. CLASS 111 27" RCP
OEPLACE ALLEY PAVEMENT
'Y' INLET
10' INLETS
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P G EX. 24'LAfE IL
INSTAL , 21 LATERAL-
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N FIGURE VII - 10
SITE J
SANDY KNOLL DR. &
0 100 200 300
SHADOWCREST LANE
SCALE IN FEET DRAINAGE IMPROVEMENTS
0