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Item 7A TNP Review of Drainage Study stn P 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 76102-81 7.336.5773 Dallas-17304 Preston Road,Suite 1340-Dallas,Texas 75252-21 4.461.9867 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,Finn 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, to p League nail &perkins Niraj Acharya,P.E.,CFM nacha rya&tnpinc.com 817.665.8202 2