ST9902-CS131015
Halie Hernandez
From:Andrew Luce <ALuce@TNPINC.com>
Sent:Tuesday, October 15, 2013 2:31 PM
To:Keith Marvin
Cc:Casey McBroom; Chris Schmitt; Michael Garza
Subject:RE: W. Sandy Lake Road
Attachments:HGL Calculations (PETTERSON).xlsx.pdf; Inlet Calculations (PETTERSON).xlsx.pdf; SD
PROFILE.pdf; DA MAP.pdf; Drainage Calculations (PETTERSON).xlsx.pdf
Keith,
Upon a cursory review, the short answer is the 100-yr HGL will remain below proposed ground, but it will increase the
hydraulic gradient by as much as 2.5’ by the end of SD Line ‘F’.
Placing a 10’ inlet at STA 84+75 would subdivide drainage area F-11 placing 5.43 cfs of flow 291’ upstream (and thus
forcing the system to carry it that much further) of where it was originally designed. This not only increases the hydraulic
gradient in SD ‘F’ for 291’ and adds another head loss at the additional lateral, but it also increases the head loss at SD
STA’s 16+29 and STA 14+54.
I have attached some quick exhibits showing the new HGL and the accompanying drainage calculations with cells
modified from the signed and sealed plans highlighted.
If you have any questions, please let me know.
Thanks,
Andrew
From: Keith Marvin [mailto:KMarvin@coppelltx.gov]
Sent: Monday, October 14, 2013 4:55 PM
To: Andrew Luce; Casey McBroom
Cc: Chris Schmitt; TTabor@TTC-PLLC.com; Michael Garza
Subject: W. Sandy Lake Road
Andrew,
The city has been approached by the developer of the Nancy J. Petterson property about the possibility of adding an
additional inlet on the north side of Sandy Lake at or around station 84+75. This would allow them to slope their street
down from Sandy Lake, but not take on any of the water in the gutter. They are asking us to price this addition through
the contractor, but before we do that I wanted you to give a cursory review of the drainage design to ensure we would
not cause a capacity problem in the system if we picked up this water at that location.
Since line F is already in place, a capacity problem that would require us to increase the pipe size would now involve
removing and replacing a portion of the line.
Please take a look at this and give me your thoughts.
Thank you.
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Keith Marvin, P.E.
City of Coppell
972-304-3681
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