Trinity Shores-CS011015 FILE
October 15, 2001 ~' ~ ~ ~ ~
Houshang Jahvani
Jahvani Engineering Associates
2125 N Josey Lane, Suite 202-B Post-it~' Fax Note 7671 Oatelo/]~>/O! [#of ·
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Carrollton, TX 75006 T°/~/]~']~aC) [~/~-~')~ N"~ Fr°m]~X~ C'v'[~/ ~ ~l
Co.;Dept. ~o.
RE: Trinity Shores Estates ~o~.
Construction Plan Review Comments Fax #~/-/~. ~ ~ I ] 0 ~' Fax #
Dear Mr. Jahvani:
The City of Coppell has reviewed the referenced plans and has the following comments to offer:
Construction Details-
These should not be included with the construction plans. All contractors working on the project
are required to have a complete set of the City of Coppell Standard Construction Details onsite at
all times. Therefore, Sheets 12 - 19 should be removed from your construction plans. The only
details that should be provided with your plans are special details particular to this project.
Final Plat-
The 10' drainage easement behind Lots 3, 4, 5, & 6 of Block A should be either made private or
have a public drainage system installed. This is addressed further in comments dealing with
drainage issues. Also on the plat, provide the Floodplain Map number for the 100-year
floodplain on Lot ! 1, Block A.
Sheet 3 -
1. As previously stated, you should provide a drainage system along the rear of Lots 3, 4, 5 & 6,
Block A to accommodate the flow of water from the west of this subdivision. In the past we
have utilized drainage systems with yard inlets or in some instances, a concrete flume that
conveys the drainage to a 'Y' inlet. Please make the appropriate revisions.
2. Please provide details for the retaining wall. This would include items such as: type of
material, footing, a screening wall on top, etc. You should also provide the top of the wall
elevations, and the ground elevation at the foot of the wall on both the east and west side of
the wall.
3. You will need a letter of permission to grade on both the Harrington property and the golf
course to the south.
4. Note # 5 on the plat states that a fence is required. How is the area on Lots 14 and 15 that
contains the proposed 'Y' inlet going to be maintained? With a retaining wall and a
proposed fence on top, there will be no access to this area. Has there been any consideration
to obtaining a drainage easement fi'om the Harrington site to install the system at the
southwest comer of the Harrington property? I'm not suggesting that is the answer to this
situation, but you do need to address the maintenance of the area that will be isolated from
Lots 14 and 15.
255 PARK'4VAv It PO [~O~, .176 * COPP£LL TX 75OI9 ~' TEL 972.'A62 0022 * FAX 972:304 3673
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5. Please provide details on how the proposed retaining wall on Lots 14 and 19 transitions back
to natural ground.
6. As previously stated during the Development Review process, an offsite easement will be
required for construction of the drainage system to the Elm Fork of the Trinity River.
Sheet 4 -
1. Note # 5 should be changed to state that the contractor is required to provide a maintenance
bond for 2 years at 50% of the construction cost.
2. Need to show the existing ground for both the right and left right-of-way lines for your street
profile.
3. The finished pad and finished floor elevations should be provided, not just zeroed out.
4. As previously stated the typical cross-section for the 28' concrete street should be removed
as that is covered in our Standard Details. Also, please note that the street should be
constructed with a parabolic crown, not a rooftop crown.
5. Prior to the approval of these construction plans, you should provide a revised Sandy Lake
Road design that shows the relocation of the low point inlet that conflicts with your curb
return.
6. Your proposed street location is in a transition area for proposed Sandy Lake Road that
narrows the paving as it approaches the bridge. This will create a situation where your east
curb return becomes a dangerous obstacle to vehicles traveling east, i.e., your street removes
the entire curb line transition and your east curb line will then encroach approximately 5' into
the street. This needs to be resolved prior to approval of these plans. Resolution will involve
a redesign of the Sandy Lake Road plans or the relocation of your street. For additional
information on this, please reference Sheet 24 of 94 of the proposed Sandy Lake Road
Reconstruction Plans.
Sheet 5 -
1. As previously stated, a drainage system is required at the rear of Lots 3-6, Block A that will
accommodate Drainage Area 2.
2. All pipes at a low point should be a minimum of 21" diameter, not 18" as shown. This
includes the pipes serving the 'Y' inlets also.
3. Drainage Area 5 is currently zoned Retail, therefore, you should utilize a nm-off coefficient
of 0.9, not 0.45. Also the time of concentration for drainage in Area 5 should be 10 minutes,
not 15 minutes. The appropriate revisions should be made to your onsite inlet data and onsite
drainage area data charts. Also, Drainage Area 4 needs revision to show the correct time of
concentration. I have questions about the gutter slope and capacity for Drainage Areas 1, 2
and 5. You are showing those gutter slopes to be 0.5 as if they are draining in the street when,
in fact, they drain across open land. Both onsite and offsite data charts need revisions.
Sheet 6 -
1. Show the existing 54", 48" and 21" RCP's in Sandy Lake Road.
Sheet 7 -
1. Profile View - this supposedly corresponds to the plan view on Sheet 6, however, most of the
pipe diameters are shown differently on the two sheets. The station locations for junction
boxes, etc. are also shown differently on the two sheets. Please be advised that you need to
submit plans where the profile and plan view information matches. The City of Coppell does
not perform quality control for proposed designs. The drainage design as submitted will not
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be reviewed until correct and consistent pipe sizes and junction box locations, etc. have been
shown.
2. When you revise your plans, also please make note of the following comments:
a) The outflow velocity at 12' per second as it approaches the Elm Fork is too fast. Even
though you provide a short flattening of the 30" RCP, you should consider a much longer
flattening of the RCP to insure the velocity is slowed before the outfall.
b) All hydraulic grade lines should be shown on the plans.
c) On line ST-2 you are showing the top of the 'Y' inlet lower than the 100-year design. Please
be advised that this system will not function. You should design a system that functions
during a 100-year storm. For some of the property that has previously developed along the
Elm Fork of the Trinity River, I have allowed engineers to establish the starting hydraulic
grade line water surface at the outfall of their pipe to coincide with the 1 O-year elevation for
the Elm Fork. Regardless of how you approach the redesign, be advised that the hydraulic
grade line or the 100-year water surface cannot be above the opening of the inlets. This is
happening for your design at Station 1+80 line ST-2 as shown on the profile, or Station 1+99
line ST-2 as shown on the plan view. I'm not sure which stationing is correct.
d) Again, please be advised that all pipes serving low point 'Y' inlets should be a minimum 21"
diameter.
Sheet 8 -
1. The proposed clean-outs at Station 3+67 line 'B' and 3+80 line 'C' should be constructed as
standard manholes, not clean-outs.
2. You should reconsider the location of your proposed fire hydrant adjacent to Lot 11. The
current location could hinder the future construction of driveway access to this lot. You
should consider the possibility of relocating the hydrant to a common property line.
3. Please comment as to why you are proposing to install a 12xSx8 tee at the east end of the
extension of the 8" water line adjacent to Lot 19.
4. On your Utility Plan you should also show the proposed drainage lines and inlets, as they
could potentially conflict with proposed fire hydrant locations. Also, show the proposed
sanitary sewer and water lines on the Storm Drain Plan view.
Sheet 9 -
1. Show the existing ground for your profile views.
Please make the necessary changes and re-submit these marked-up plans and two sets of
revised plans to the City for review. If you have any questions, please contact me at (972) 304-
3686.
Sincerely,
Kenneth M. Griffin, P.E.
Director of Engineering & Public Works