Item 5 & 6- Drainage Study Reviewtnp
August 30, 2016 teague nail & perkins www.tnpinc.com
engineers
surveyors
landscape architects
City of Southlake
Department of Public Works
Attn: Steve Anderson, P.E.
1400 Main Street, Suite 320
Southlake, Texas 76092
RE: White Chapel Village Drainage Study — l st Review
Mr. Anderson,
We have completed our review of the drainage study for White Chapel Village. The analysis included a
written report, limited hydraulic modeling data, and appendices containing previously -completed drainage
studies in the watershed. We recommend that the following comments be addressed prior to acceptance of
the drainage study.
General Comments
1. The report should include a site plan, drainage area maps, and calculations pertaining to the
White Chapel Village development.
2. Evaluations of all systems should include comparison of pre -developed vs. post -developed
conditions.
3. One of the intents of the submitted study is to determine the availability of additional capacity
in the existing Carillon ponds. However, in order for this to be conclusively determined, the
study must utilize the Jacobs' detention study as a base and update those models to reflect any
corrected and proposed/post-developed conditions.
4. The study includes hydraulic models with a *.HXP file extension. We are unable to open these
models. Hardcopy tabular input/output should be provided. Conversely, it appears that the
same systems may have been analyzed using StormCAD. If this is the case, digital StormCAD
models and tabular output can be provided.
5. The study indicates that the open channel downstream (north) of SH 114 has not been analyzed
as it is a state of disrepair and is to be improved by others prior to the construction of White
Chapel Village. Please provide reference plans that indicate the proposed improvements and
correspondence indicating that it is to be constructed prior to White Chapel Village.
6. It is unclear as to why the condition of the existing channel (referenced in Number 5, above)
impacts the ability to analyze channel capacity. This channel should be analyzed for pre- and
post -developed conditions to validate that it can convey developed discharges.
7. The analysis should include evaluations of the system between Southmont and the ponds.
8. Please note that redirection or re-channelization of the unnamed tributary could require US
Army Corps of Engineers Section 404 permitting.
9. Provide Tc calculations.
10. The study should include the effective FIRM map for reference purposes.
Fort Worth - 1 100 Macon Street -Fort Worth, Texas 76102- 817.336.5773 Dallas - 17304 Preston Road, Suite 1340 -Da I las, Texas 75252- 214.461.9867
Denton - 1517 Centre Place Drive, Suite 320- Denton, Texas 76205-940.383.4177 ♦ Sherman - 200 North Travis Street, Suite 500- Sherman, Texas 75090-903.870.1089
Registered by the Texas Board of Professional Engineers, Firm No. F-230 - Registered by the Texas Board of Professional Surveyors, Firm No. 100116-00
1 1. The Runoff "c" coefficient used should be based on the City of Southlake's "Construction Plan
Checklist." Please provide a site plan that corroborates the c value.
Please do not hesitate to contact me with any questions.
Sincerely,
tnp
League nail & perkins
Niraj Acharya, P.E., CFM
nacharva(atnpinc.com
817.665.8202