ST8402-CS 890615 (3) GINN, INC.
June 15, 1989
CONSULTING
Mr. Russ~ Doyle, P.E. __
City of
P.O.
Coppe TX 7501
Re:
Tap
From Sandy Lake
;reet Flooding
to Denton ~ek
Station
JL} I t5 1989
Dear Mr.
Despite the measures as per my letters dated
May 17, 1989 and copies attached, flooding of the
outside lane of the new southbound pavement between Stations
176+50 and 177+80 has continued during the recent persistent
thunderstorms. We have found it to be necessary for the
protection of the lives, safety and property of the traveling
public on Denton Tap Road to order the Contractor to expose
lateral D-13a and install an "X" inlet and connecting piping
along with a relief berm and swale diverting some of the
excessive runoff from the modified inlet and temporary berm at
Station 176+50.
In addition to the previous modifications to the inlet at Station
176+50 this should greatly reduce the amount of runoff getting
onto the road and reduce the hazard to the traveling public. The
pipe and inlet work will be paid for at the applicable Contract
unit Prices, and the required earthwork will have to be paid for
in accordance with extra work provisions of the Contract.
On Friday, June 9, 1989, I met with the Contractor and one of the
owners of the adjacent property, Mr. Glen Hincktey, to discuss
the immediate construction of this proposed storm drainage relief
system. Mr. Hinckley, has been extremely helpful and cooperative
in allowing this work to proceed as soon as possible. Mr.
Hinckley did request that we stipulate that the improvements
mentioned herein are temporary and that he may cause them to be
either removed or modified when his property is developed.
We have assured Mr. Hinckley that when his property develops, he
may remove or modify the storm sewer "X" inlet and the swale and
berm in order to extend the storm sewer system as necessary for
the development of his property and any adjacent roadways. It
should be noted that Mr. Hinckley's property, in its current
condition, drains to Denton Tap Road and as such, its developed
runoff can be accommodated in the Denton Tap Road storm sewer
system.
17103 Preston Road · Suite 100 · LB 118 · Dallas, Texas 75248 · Phone 214/248-4900
GINN, INC.
CONSI LTING ENGINEERS
June 15, 1989
Mr. Russ~
city of
P.O.
Coppe]
Re:
Doyle, P.E.
)ell
TX
:on Tap(
rom Sandy\Lake
reet Flooding
:,ad to Denton ,ek Station
Dear Mr. ~:
Despite the measures as per my letters dated
May 17, 1989 and copies attached, flooding of the
outside lane of the new southbound pavement between Stations
176+50 and 177+80 has continued during the recent persistent
thunderstorms. We have found it to be necessary for the
protection of the lives, safety and property of the traveling
public on Denton Tap Road to order the Contractor to expose
lateral D-13a and install an "X" inlet and connecting piping
along with a relief berm and swale diverting some of the
excessive runoff from the modified inlet and temporary berm at
Station 176+50.
In addition to the previous modifications to the inlet at Station
176+50 this should greatly reduce the amount of runoff getting
onto the road and reduce the hazard to the traveling public. The
pipe and inlet work will be paid for at the applicable Contract
unit Prices, and the required earthwork will have to be paid for
in accordance with extra work provisions of the Contract.
On Friday, June 9, 1989, I met with the Contractor and one of the
owners of the adjacent property, Mr. Glen Hinckley, to discuss
the immediate construction of this proposed storm drainage relief
system. Mr. Hinckley, has been extremely helpful and cooperative
in allowing this work to proceed as soon as possible. Mr.
Hinckley did request that we stipulate that the improvements
mentioned herein are temporary and that he may cause them to be
either removed or modified when his property is developed.
We have assured Mr. Hinckley that when his property develops, he
may remove or modify the storm sewer "X" inlet and the swale and
berm in order to extend the storm sewer system as necessary for
the development of his property and any adjacent roadways. It
should be noted that Mr. Hinckley's property, in its current
condition, drains to Denton Tap Road and as such, its developed
runoff can be accommodated in the Denton Tap Road storm sewer
system.
17103 Preston Road ® Suite 100 · lB 118 · Dallas, Texas 75248 · Phone 214,248-4900
We suspect that the excessive runoff which is flowing across the
Hinckley property may be partially a result of the increased
runoff from Skaggs shopping center, the inadequate drainage
system for Shady Dale Estates, and some filling of old gravel
pits on the adjacent property. The box culvert which is to be
extended south from the high school site may provide the solution
to this flooding problem. We recommend that this situation be
addressed in the on-going efforts to have the abovementioned box
culvert constructed.
We will continue to monitor the effectiveness of the
abovementioned modifications to the drainage system and attempt
to ascertain the principal sources of the excessive stormwater
runoff. Please call me if you have any questions.
Sincerely,
John C. Karlsruher, P.E.
Project Engineer
JCK/dsp
cc:
Glen Hinckley
Scott Balch
H. Wayne Ginn,
Randy Fleming
File 379/280
enclosures
GINN, INC.
May 17, 1989
CONSULTING ENGINEERS
Mr. Russell Doyle, P.E.
City Engineer
City of Coppell
P.O. Box 478
Coppell, Texas 75019
Re: Denton Tap Road Improvements from Sandy Lake Road to Denton
Creek - Handwritten Memorandum dated 5-3-89.
Dear Mr. Doyle:
This letter is in response to your Handwritten Memorandum dated
May 3, 1989, copy attached. During the recent rains resulting
from heavy thunderstorms our resident project representative
observed the lane flooding situation in the vicinity of the storm
water inlets along the west curb line at project stations 176+50
and 177+80. Based on the field reports we have received and your
verbal and written inquiries, we have been studying the situation
in search of both long and short term solutions to the lane
flooding recently experienced. We will address the specific
issues raised in your Memorandum, and then cover the critical
elements of the potential solutions identified.
As you are aware, intense rainfalls are usually associated with
the frequent heavy thunderstorms typically experienced in this
locality at this time of year. Street flooding occurs both
during the rainfall and until the resulting significant run-off
subsides. This lane flooding cannot practically be eliminated in
most cases. Typically, as in the City of Coppell, the enclosed
storm sewer systems are designed to handle the stormwater run-off
from a 100-year storm and the on-grade inlets are designed to
remove stormwater run-off generated from a 5-year storm from the
gutters. During more intense storms the inlet capacity is
temporarily exceeded and storm water is allowed to pond in the
designated traffic lanes for the duration of the event which
produces stormwater run-off in excess of the design capacity of
the inlets.
The subject roadway has been designed in accordance with the City
of Coppell Standard Construction Details, and as such has a
standard cross slope of 1/4" per foot in the area of concern.
The longitudinal slope (gutter slope) is essentially 0.5%. It
should be noted that a grade change occurs at station 176+50, the
location of the more southerly of the two inlets in question.
This partioular inlet was located at the grade change in order to
remove as much gutter flow as possible before it reached the
lower gutter capacity of the paving section immediately downslope
of the grade change.
17103 I'rcaton Road · Suite 100 · I.B 118 · I)all;c~,'l'cxa,'; 75248 · I'honc 214/248-4900
The current problem appears to be related to the fact that
portions of the adjacent properties which were not originally
included in the drainage area for this project may have been
recently graded in such a fashion that they now contribute run-
off to this project. Additionally it appears that the run-off
'flow is concentrated in a couple of areas, rather than being a
sheet flow condition for which the storm drainage system was
originally designed. Compounding the above, the slopes behind
the property line of the adjacent property cause the run-off to
flow further out into the roadway than originally anticipated.
The long term solution to this problem is related to the fact
that the adjacent property in the area of concern is currently
undeveloped. In anticipation of the ultimate development of the
property, a storm sewer lateral stubout (lateral D-13a) has been
provided from the main Denton Tap Road storm sewer system, as a
part of the original project design, to provide for the developed
storm water run-off from the adjacent properties. In order to
accomplish this long term solution, the adjacent property owners
must design and build an onsite extension of the existing storm
drainage system as a part of the development of their properties.
This morning we were notified of the closure of Denton Tap Road
between Sandy lake Road and Parkway Blvd. as a result of the
recurrence of the lane flooding due to the heavy thunderstorms
experienced last night and this morning. .After traveling to the
site this morning and observing the lane flooding situation, we
directed the Contractor to create openings at the rear of the
inlet at station 176+50 and grade the slope immediately behind
the inlet to the bottom of the openings. We also had the
Contractor deposit excavated materials in such a way as to
collect the run-off at the property line and funnel it into the
back opening of the inlet. The work and street cleanup was
completed by 2:30 P.M. this afternoon and the road opened to
traffic at that time.
If the above method of temporarily controlling the run-off
discharges from the adjacent property is successful we may have a
concrete riprap flume constructed at the rear of the inlet as a
temporary measure until the property develops.
Please call me if you have any questions.
Sincerely,
John C. Karlsruher, P.E.
Project Engineer
attachment
H. Wayne Ginn, P.E.
Randy Fleming
File 379 (A:DENFLOOD)
HANDWRITTEN MEMORANDUM
GINN, INC.
June 5, 1989
CONSULTING ENGINEERS
Mr. Scott Balch, P.E.
L.H. Lacy Co.
P.O. Box 541297
Dallas, TX 75354-1297
Re:
Denton Tap Road Improvements from Sandy Lake Road to
Denton Creek - Outside Lane Flooding Southbound Lanes
from Sta. 176+50 to Sta. 177+80
Dear Mr. Balch:
During yesterday morning's thunderstorms I observed flooding in
the southbound lanes between the inlet at Station 176+50 and the
one at 177+80. The runoff which was entering the street was from
the "overflow channel" which was constructed immediately north of
the inlet at Station 176+50 as a part of your efforts on May 17,
1989. The rear openings in the inlet at Station 176+50 worked
very well and will handle the additional flow if the "overflow
channel" is closed. Please have the "overflow channel" filled as
soon as possible in order to prevent excessive ponding of water
on the roadway in this area in future thunderstorms and rainfall
events.
While observing the above, I also noticed what appears to be an
indication of deviation from the profile grades shown on the
Drawings in this area. Some stormwater runoff flows south into
the inlet at Station 176+50 instead of going north as it should
in accordance with the plans. Also, the ponding width indicates
that the pavement crossfall from the median to the outside
curbline may be too flat. Please have your surveyor check your
profile and crossfall grades in this area and submit your
findings in writing to us for review.
Please refer to the attached marked blueline print of Sheet 13 of
56.
We appreciate your cooperation in this matter.
Sincerely,
John C. Karlsruher, P.E.
Project Engineer
JCK/dsp
enclosure
cc: Russell Doyle, P.E.
H. Wayne Ginn, P.E.
Randy Fleming
File 379
17103 Prcaton Road ·Suitc 100 · LB 118 ·Dallas, Tcxas 75248 · Phonc 214/248-4900