HomeMy WebLinkAboutLetter to StaffKimley»>Horn
Memorandum
To: Danielle Singh, P.E.
From: Tyler Lewis, P.E.
Subject: THE BARRACKS DETENTION FACILITY MOO/FICA TIONS (OP)
Date: November 10, 2014
This memorandum is to address the City of College Station Staffs comments on the above
mentioned project as received by Kimley-Horn and Associates, Inc. in the letter dated August 19,
2014. The following information has been included in this submittal for your review.
• 1-Full Size set of Construction Plans
• Drainage Report
Please find the written responses to comments on the following pages.
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Engineering Comments No. 1 -$
1. We have received the updated preliminary plan since your original submittal. P13 ./I
does not include 5 acres of open space, this is mostly designated for multi-family. -~
P14 is also unlikely to be developed with 5 acres of open space. P6 includes ~
commercial to be developed with the Barracks though this is shown as open space. i
The submitted design includes the latest land plan received from Schultz
Engineering 11/4/2014. P13 now includes 8.65 acres of townhome, 1.2 acres of)
multifamily, and 3.66 acres will be left in existing conditions (requiring the
future development to include site specific detention). It was communicated to
KHA that 3.35 acres of P14 be designated as multifamily, which is now
reflected in the weighted impervious calculations. The land use in PG has been
revised to eliminate the original commercial portion and only have townhome
(15.06 acres) and open space (0.70 acres).
/2. On the proposed cond ition drainage area map, the Watershed Information table was
not updated with the changes to this report.
The watershed information table on the proposed condition drainage area map
has been updated.
3. The City will not maintain the storm sewer pipes between Pond 1 and Pond 2 except
within the ROW of General Parkway. Please show an additional junction box on the
northeast side of General Parkway.
An additional junction box has been added on the east side of General Parkway
for each of the 36" lines to demark the public and private portions.
4. It appears that the weir for Pond 1 will not properly drain, with higher
elevations immediately downstream of the weir. How do you propose to
address this situation?
This issue has been addressed per the original construction plans. The weir
now freely drains.
5. Are the tables provided produced by SWMM? If not, please provide SWMM output
for reference.
The SWMM output tables are now included in the appendix of the report for
each existing and proposed conditional run for the 2, 10, 25, 50, and 100 year
events.
6. In Appendix D, Downstream 100 Year Hydraulic Conditions, please explain why the
flow is decreasing as it moves downstream. For instance, at station 7431 the flow is
less than half of the flow leaving the site wh ich is immed iately upstream.
The SWMM model is an unsteady state model that accounts for storage in each
link, based on its geometry. This storage attenuates the flow, similar to a
detention pond, so peak flow can decrease as you move downstream. The
amount of storage in a link will affect the amount of attenuation.
7. Please label rip rap downstream of Pond 4.
200 SY of TxDOT Type 'R' riprap is called out at the outfall of Pond 4.
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Where is the emergency spillway for Pond 2?
Since Pond 2 only receives flow from the interconnect with Pond 1 and
precipitation that falls directly into the pond. The plugged flow condition
reaches a lower peak water surface elevation than in normal conditions.
9. On Sheet 8, Pond 3 discharge is listed as 3325.43 cfs. Please revise .
The peak outflow from Pond 3 is 346.26 cfs. This has been revised on sheet 8.
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