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FS0001-CS010320Kimley-H0rnand Associates, Inc. Z~ ~ ----/,-z) ~ ~'! '~ ~ ~,..~ .~ V ¥~ Suite 1800 C~Jl X~"OODallas,12700ParkCentralgriVeTexas L," ~1 ~J~ 75251 March 20, 2001 VIA FACSIMILE 972.304.3673 HARD COPY VIA U.S. MAIL 8 pages total Mi'. Ken Griffin, P.E. Dii'cctoi' of Engineering and ?ub]ic Woi'ks City of Coppe]l ?.O. Box 478 Coppcll, 'TX 75019 Re: Resubmittal Review CLOMR and CDC Application Estates of Denton Creek Coppeil, Texas Dear Ken: Kimley-Hom and Associates, Inc. (KHA) has performed a review of the resubmittal of the Estates of Denton Creek FEMA CLOMR Request for the 32.09 acre Holmes Tract, prepared by Nathan D. Maier Consulting Engineers, Inc. (NDM), dated January 2001. The resubmitted Corridor Development Certificate (CDC) application was also reviewed. This letter is set up to show the KHA comments from NDM's previous submittal that were addressed and any additional comments by KHA. The submitted report includes only data to apply for a Federal Emergency Management Agency (FEMA) Conditional Letter of Map Revision (CLOMR). NDM's report does not address some issues related to the City's Floodplain Management Ordinance, such as fully developed flows. KHA reviewed the document for adherence to FEMA criteria and has also noted instances where City criteria may not have been met with respect to the City Floodplain Management Ordinance or Subdivision Ordinance. · TEL 972 770 1300 FAX 972 239 3820 Kimley-Harn and Associates, Inc. C,y of Coppell. March 20. 2001. Page 2 1. The Effective and Annotated Flood Insurance Rate Maps (FIRM) showing the project impact to the FEMA floodplain/floodway are not readable in KHA's report copy. Please provide readable copies of these exhibits. Comment cleared. Readable copies were included in the resubmittal. 2. On page one of the narrative report, it reads "The resultant water surface elevations due to the proposed grading of the Estates of Denton Creek...". This statement implies that there will be modifications to the floodplain elevations, while the remainder of the report maintains that the base flood elevations (BFE) for Elm Fork or Denton Creek will not change. Please provide clarification in the narrative. Comment cleared. The comment was removed from the narrative, but no clarification was given. 3. The FEMA 100-year Floodplain reclamation proposed in this CLOMR could be accomplished using a CLOMR - F (CLOMR based on fill). Please explain the reasoning behind pursuing a CLOMR for this proposed reclamation. Comment cleared. This comment was not addressed, but it is at the option of the engineer and the City to determine by what means the floodplain is reclaimed via FEMA. 4. The included FEMA MT-1 Form 3 outlines criteria for fill compaction and erosion control in the FEMA 100-year floodplain. It is suggested that this information be required on the grading plan for the site. Suggestion stands. The requirements outlined on the forms should be included on the plans or in the construction specifications. 5. The Post-Project Conditions Work Map shows a portion of multiple lots will be located in the FEMA floodplain. It is suggested that the engineer be made aware of Subdivision Regulation Appendix C, Section 11.5 a/b covering access to this floodplain area for maintenance and provide for this access via easements or other means. Suggestion stands. While this comment does not pertain to the CLOMR submittal, it is important that the development plans and final plat allow for this access. Kimley-Horn and Associates, Inc. City of Coppell, March 20, 2001, Page 3 6. The FEMA floodway should be shown on any workmaps showing the FEMA floodplain. Comment cleared. The FEMA floodway has been included on the enclosed exhibits and workmaps. 7. On FEMA MT-2 Form 1 Section 5, it states that the community will be responsible for performing maintenance on flood control structures associated with this project. The submitted CDC forms indicate that the owner will be responsible for maintenance. Clarification of this responsibility should be provided. Comment cleared. The CDC form now matches the FEMA CLOMR forms. The City of Coppell has been deemed responsible for maintenance on flood control structures associated with this project. 8. The HEC-2 model for Denton Creek and HEC-RAS model for the Elm Fork of the Trinity River are provided as supporting documentation to this report. The HEC-2 model includes existing condition geometry with fully developed condition flows. This model results in water surface elevations through the project reach that may inundate the site during a large storm event. This is evident comparing the resultant water surface elevations from the HEC-2 model to the grading shown on the Post- Project Conditions Work Map. It is also important to note that this model would not typically be included in a FEMA CLOMR submittal, rather the FEMA effective model for Denton Creek would be included. The narrative report states that the site falls within the ineffective flow area of the Sandy Lake Road Bridge over Elm Fork. For this reason, the narrative concludes that the effects of Denton Creek should not govern this floodplain. It is suggested that the engineer provide the FEMA effective model for Denton Creek with any necessary geometry modifications (if proposed) and address the concern stated above regarding the fully developed floodplain. The FEMA effective model for Denton Creek will need to be evaluated to see if those water surface elevations pose a flooding hazard to the proposed development, or an alternate explanation provided. and Associates, Inc. City of Coppell, March 20, 2001, Page 4 Comment open. It is unclear in the submittal if the HEC-2 model for Denton Creek is the FEMA Effective model. Please provide documentation or a comparison to the FIS to clarify. FEMA could ask for this clarification as part of their comments. The HEC-2 model resubmitted for Denton Creek contains two profiles. The first profile is existing condition FEMA discharges. The second profile is the 2-year fully developed profile. NDM dropped the 10-year and 100-year fully developed profiles from that model, but did not drop the 2-year profile. FEMA will likely ignore the profile, but may return the submittal for clarification. NDM has addressed the final comment under No. 8 above. An explanation is provided in Section 5.0 of the narrative showing how the 100-year water surface elevations in the Elm Fork of the Trinity River control the Denton Creek 100- year floodplain. While not necessary for a FEMA submittal, there is still concern regarding the 100-year fully developed flows in Denton Creek. According to the original HEC-2 model submitted by NDM, water surface elevations through the project reach still may inundate the site during a large storm event. This is evident comparing the resultant water surface elevations from the HEC-2 model to the spot elevations shown on the Post-Project Conditions Work Map. This concern should be addressed by NDM at some point in the development plan process. 9. Digital models have not been included with the CLOMR submittal. It would be helpful in review if these models could be provided. FEMA typically will request digital copies of the models used. Comment cleared. Digital models were included in the resubmittal. 10. The Post-Project Conditions Work Map includes topographic contours to show the elevation of the site out of the 100-year FEMA floodplain. The narrative report states that the fill will be 2 feet above the BFE. At the northern end of the project, the BFE varies from 447.07 feet to 447.44 feet. The contours for the proposed fill in this area show 449 feet. Spot shots showing the proposed fill 2 feet or greater above the BFE should be shown on both the Work Map and reflected on the site grading plan. Comment cleared. Grading spot elevations are now shown on the Post-Project Conditions Work Map. The Work Map now matches the narrative. Kimley-Horn and Associates, Inc. City of Coppell, March 20, 2001, Page 5 The CLOMR report is substantially complete for submittal to FEMA. Comment No. 8 from the previous submittal remains open. That comment should be addressed by NDM at some point in the development plan process as determined by the City. It is not required by FEMA that the fully developed flows be addressed. The follow/ng comments pertain to the CDC application included with the resubmittal package. The format is the same as the previous CLOMR submittal comments. 1. A detailed Site Plan needs to be provided for adequate review of the CDC application. This site plan should include the items outlined on the application. Comment cleared. A detailed site plan was included in the resubmittal. 2. The hydrologic and hydraulic information included on Part 2 of the CDC form does not correspond to the FEMA regulatory information provided in the CLOMR report or the profiles and cross sections provided as attachments to the CDC application. Digital copies of the models should also be included. Please have the engineer provide the proper backup information for the forms. Comment open. The hydrologic and hydraulic information included in Part 2 of the CDC application still does not match the information in the CLOMR request. KHA reviewed the electronic models provided by NDM and noted multiple slight discrepancies between the two models. It is suspected that two base models may have been used by NDM to create the submittals, one from the U.S. Army Corps of Engineers, and one adapted by NDM. NDM should provide clarification for the discrepancies and correct the submittal if necessary. Profile outputs from the CDC and CLOMR HEC-RAS models are included as an attachment to this letter. Standard CDC Form Part 2 does not correctly reflect the upstream boundary for the project in the 100-year flood event. The upstream boundary of the project is HEC-RAS cross section 97919 as evidenced by the data in the table. The velocity shown for the channel at the upstream boundary is from the next cross section downstream of 97919. The form should be adjusted to match the correct HEC-RAS model as determined from addressing the comment in the above paragraph. Kimley-Horn and Associates, Inc. City of Coppell, March 20, 2001, Page 6 3. Design and calculations for the valley storage mitigation swale should be included with the CDC applications. They currently are not included. Comment cleared. Valley storage calculations were included in the resubmittal. 4. (New Comment) Exhibits 4A, 4B, 5, 6A,and 6B call out the East Fork of the Trinity River as the subject reach for the site. This site falls on the Elm Fork of the Trinity. This should be corrected on the exhibits before submittal. No formal response to this comment is necessary. The CDC application is substantially complete for submittal. The submittal could require further review, based on NDM's response to open comment No. 2 above. Review of NDM's reply by KHA is at the discretion of the City Engineer, and can be performed on an hourly basis per our agreement. Additional comments to the ones listed above may be generated as a result of the reply to the above comment. The City should evaluate the proposed development for impact to and influence from the Denton Creek fully developed floodplain. The City should also coordinate the application for the CDC with the U.S. Army Corps of Engineers and be copied on transmittals from NDM to the Corps, TNRCC, etc. to see that the City's requirements are met in this regard. Please feel free to contact me if you have any questions or concerns, or need clarification of the comments. Sincerely, Kimley-Horn and Associates, Inc. Dan F. Grant, E.I. Project Manager /dfg Attachments - CLOMR Submittal HEC-RAS Profile Table CDC Submittal HEC-RAS Profile Table G:~IYDROyrojects\63124004\CorrespXLetO2Cty. doc cc: Mike Boyd, P.E. - Nathan D. Maier Consulting Engineers, Inc. - Via Facsimile & Mail Plan: 10,50, & 100 River: Elm Fork Reach: ef3 ~ t~:~ 31600.00 422.71 449.26 446.00 449.34 0.000210 2.02 20151.63 4218.30 0.11 31600.00 420.20 448.98 441.75 449.08 0.000384 3.78 20393.68 5700.01 0.16 i:i; 31600.00 418.75 448.79 442.24 448.85 0.000286 3.19 24006.11 5727.22 0.14 ;,: ,,, ~ 31600.00 419.00 448.45 445.79 448.55 0.00054~ 4.43 19861.67 5255.84 0.18 ~J 42900.00 419.80 448.03 444.01 448.07 0.000120 1.81 31534.77 6843.29 0.09 i~ 42900.00 418.90 447.9! 443.92 447.98 0.000132 2.12 32304.51 7301.67 0.09 ~i~ ~t 42900.00 417.60 447.81 444.10 447.84 0.000145 2.41 33607.97 7704.08 0.10 ~ 42900.00 416.90 447.66 444.12 447.70 0.000183 2.88 33011.64 6627.43 0.12 !!~ ~'~i';~ 42900.00 416.20 447.44 443.92 447.48 0.000325 3.07 33162.39 9125.75 0.14 42900.00 416.50 447.07 444.90 447.18 0.000600 4.36 25205.72 5250.00 0.19 ~ 43500.00 417.30 444.66 441.64 445.20 0.001411 7.56 11215.89 2220.00 0.31 ~;f~ ~ ~ 43500.00 417.50 443.67 438.18 444.32 0.001541 7.50 7235.27 1060.34 0.32 ~ 43500.00 417.50 443.49 439.47 444.24 0.000654 8.99 7839.55 1019.43 0.35 ~?;~ ~ ~ Bridge ~~ 43500.00 417.50 443.47 439.19 444.07 0.001383 7.84 7827.60 1019.37 0.31 ~ 43500.00 417.50 443.50 438.50 444.03 0.001346 7.17 8034.56 1000.00 0.30 ~ 43500.00 433.70 442.31 441.44 443.92 0.002712 15.01 5380.45 1000.00 0.93 ~ 43500.00 433.70 442.25 441.44 443.90 0.002803 15.18 5317.44 1000.00 0.95 ~ ~ 43500.00 410.20 443.04 431.60 443.56 0.000977 6.89 9247.99 1068.50 0.26 ~ 43500.00 410.20 442.98 431.60 443.51 0.000994 6.94 9176.98 1067.78 0.26 ~?i~ 43500.00 410.20 442.86 434.20 442.96 0.000089 2.04 17350.60 1319.75 0.08 ~ ~!~ 43500.00 410.20 442.83 432.01 442.89 0.000050 1.37 22905.10 1896.06 0.06 43500.00 409.00 442.63 431.99 442.80 0.000341 3.89 14220.44 2477,79 0.15 43500.00 408.00 442.44 436.53 442.53 0.000262 3.32 19236.12 2584.95 0.13 Plan: UTCDCl-100 River:Elm Fork Reach: ef3 35600.00 422.71 449.84 446.00 449.91 0.000241 2.24 22577.53 4223.89 0.12 ~~ 35600.00 420.20 449.53 442.46 449.63 0.000382 3.65 23518.39 5709.68 0.16 35600.00 418.75! 449.35 446.80 449.40 0,000276 3.20 27236.05 5817.79 0.13 35600.00 419.00 449.00 446.45 449.10 0,000549 4.52 22827.94 5415.65 0.18 49600.00 419.80 448,80 444,01 448.83 0.000110 1.80 36863.75 7079.53 0.08 49600.00 418.90 448.72 444.11 448,75 0.000118 2.06 38531.78 8133.72 0.09 ~,~ ~iii~ ~. 49600.00 417.60 448.60 444.32 448,63 0.000128 2.33 39961.33 8162.77 0.09 49600.00 416,90 448,47 ~ 444,36 448.51 0.000160 2.77 38430.39 6755,73 0.11 49600.00 416.20 448.28 444.24 448,32 0.000277 2.94 40878.13 9233.62 0.13 49600.00 416.50 447.98 444,90 448.06 0.000477 4.03 31588.54 8750.00 0,17 51500.00 417.30 445.82 442.55 446,33 0.001338 7.67 13774.16 2220.00 0.31 51500,00 417.50 444.77 440,81 445.45 0.001550 7.84 8455.44 1150,00 0,32 51500.00 417.50 444.51 - 440.48 445.37 0.000729 9.81 8885.08 1024,55 0,38 Bridge 51500.00 417,50 444.53 440.11 445.20 0.001510 8,48 8910,32 1024,67 0.33 51500.00 417.50 444.56 439.56 445.16 0.001465 7,77 9094.56 1000.00 0.31 51500.00 433,70 443,04 442.59 445.02 0.003028 16.81 6114,40 1000,00 1.00 51500.00 433.70 442.70 442.59 444.97 0.003638 17.94 5770.53 1000,00 1.09 51500.00 410,20 443.84 433.49 444.47 0.001146 7,65 10112.42 1078.43 0.28 51500,00 410.20 443.77 433.49 444.41 0.001168 7.71 10028,30 1077.58 0.29 51500.00 410.20 443.94 434.21 444.07 0.000102 2.27 18814.01 1466.42 0.09 51500.00 410.20 443.92 432.01 443.99 0.000064 1.62 25041.44 2044.14 0.07 51500.00 409,00 443.68 433.64 443.85 0.000357 4.12 16873.93 2538.69 0.16 51500.00 408.00 443.48 437.54 443.58 0.000282 3.57 21939.57 2613.95 0.14