Loading...
FIRM-890830KimleyHorn Kimley -Horn and Associates, Inc. �) ENGINEERS • PLANNERS • SURVEYORSi - 12660 Coit Road, Suite 200 Dallas, Texas 75251 214 386 -7007 Facsimile 214 239 -3820 ` August 30, 1989 Mr. Russell Doyle, P.E. City Engineer City of Coppell Post Office Box 478 Coppell, Texas 75019 Re: Response to the FEMA Comments Regarding the FIS Review Study Completed for the City of Coppell Dear Mr. Doyle: J_1� The purpose of this letter is to address concerns regarding the subject study completed by our office. The attached letters from the Federal Emergency Management Agency (FEMA) that were provided to us as information copies outline a number concerns regarding the City response to the FEMA Flood Insurance Study (FIS) revision. We have determined our recommendation for response to these FEMA concerns. The following are comments from FEMA and our recommendation for each response: 1. FEMA pointed out that the FIS Review Study did not include the 10- and 50 -year floods for any of the streams analyzed. This will result in the deletion of these profiles from the FIS. FEMA wants a verification that this is the City intention. The 10- and 50 -year floodplain was not determined in the FIS Review Study because FEMA has abandoned the zone determination concept and this is the only reason that these extra return frequencies would be required. Since the City's ordinance does not require analysis of the 10- or 50 -year floods, there is no reason to determine these. Therefore, it is recommended that these flood profiles be deleted from the FIS and that the City notify FEMA of this intention. 2. FEMA concluded that the FIS Review Study does not include all of the Moore Road Bridge cross sections developed in the study for the Moore Road Bridge revision. This was apparently an oversight on our part, and will be investigated and, if appropriate, corrected. This correction will be made as part of the FEMA resubmittal. According to FEMA, the starting water- surface elevations for Grapevine Creek and Denton Creek were determined using the HEC -2 tributary option. This option assumes coincidental peak flooding of the two streams. This approach is correct only when the two streams have equal watershed Anaheim Charlotte • Dallas • Fort Lauderdale • Fort Myers • Nashville • Orlando • Phoenix Raleigh • San Diego • Stuart • Tampa • Vero Beach • Virginia Beach • West Palm Beach B u i I d i n g c I i e n t r e I a t i o n s h i p s s i n c e 1 9 6 7 8- 89 /Doy t e. rwln/ 1 Mr. Russell Doyle - 2 - August 30, 1989 characteristics. This approach is always conservative in determining flood levels since it assumes the worst case. FEMA suggests that another approach would be more appropriate. They suggest the use of the slope area method to determine starting conditions. While the slope area method is generally more appropriate in these cases, it can often produce results that are unconservative. In this particular case we believe that a more conservative approach best serves the interest of City floodplain management. Since FEMA NFIP Regulations encourage more stringent applications of floodplain management, they should have no problem with a more conservative approach. Therefore, it is recommended that the coincident peak method should be used in this case. We will further investigate the floodway considerations addressed by FEMA that are impacted by use of the coincident peaking method, and determine an appropriate response to be included in the FEMA resubmittal. 4. FEMA requires that the City resolve the study differences between the FIS Review Study and that prepared by Jerry Parche for Parkway Boulevard. We have had a number of meetings with Mr. Parche to discuss the technical correlation of his model and the FEMA resubmittal. At our last meeting we agreed on a model that covered the area of Mr. Parche's project. We are now in the process of reworking our model to incorporate these changes. The changes will be reflected in the FEMA resubmittal. Mr. Parche is in the process of reworking his model, and will resubmit it to FEMA. The two models will be compatible. We have contacted Mr. Matt Miller of the FEMA Headquarters Office regarding the time frame for submittal of these response items. He said that FEMA had received a request from the City for an extension of the time allowed to respond to the FEMA concerns and that the extra time requested was agreeable to FEMA. Mr. Miller said that they would be expecting a written response by September 11, 1989. As part of our present contract with the City of Coppell to develop a watershed master plan (approved by council on August 22, 1989) we are to review and correct the present hydraulic model for the City. The work discussed above would be covered as part of that effort. Before we can prepare a response to FEMA for the items discussed we need to be sure that the City agrees with our recommendations. We suggest that you review this letter and provide your response as soon as possible so that we may proceed with the preparation of a FEMA response. If we can provide further information please call me. Sincerely, EY-HgRN AND ASSOCIATES, INC. onald orrison, P.E. Senior Hydrologist pw Attachments 8-89 /Ooyle.rwm /2 �l M N 0 0 Federal Emergency Man; Washington JD C. 20472 i i The Honorable Lou Duggan Community: City of Coppell, Mayor of the City of Coppell Dallas and Denton P.O. Box 478 Counties, Texas Coppell, Texas 75019 -Community No.: 480170 Dear Mayor Duggan: This is in response to a June 12, 1989 letter from Mr. Russell R. Doyle, P.E., City Engineer and Floodplain Administrator for the City of Coppell. In his letter, Mr. Doyle requested an update on the status of a January 12, 1989 letter in which he requested that the Federal Emergency Management Agency (FEMA) revise the September 22, 1988 preliminary Flood Insurance Study (FIS) and Flood Insurance Rate Map (FIRM) for the City of Coppell to include updated corporate limits information and the results of an untitled technical report prepared by Kimley -Horn and Associates, Inc., consulting engineers for the City of Coppell. In addition, Mr. Doyle inquired about the status of the 90- day period provided for appeals and comments on the preliminary FIS and FIRM. We have completed our review of the submitted technical report. In a July 3, 1989.1etter to you, we identified a number of concerns that must be resolved before FEMA will revise the preliminary FIS and FIRM for the City of Coppell to include the information in this technical report. Please note these concerns must be addressed within 30 days of the date of this letter. In addition, as indicated in Mr. Doyle's letter, the notice of proposed modified Base (100 -year) Flood Elevation (BFE) determinations failed to run on March 15, 1989, as we had requested. Therefore, it was necessary to schedule two new dates of publication in the Coppell Gazette as required by Section 67.4 of the National Flood Insurance Program regulations. This section requires that the proposed BFEs be published twice during the ten -day period immediately following the notification of the community's Chief Executive Officer. Accordingly, en March 29, 1089, z3-..t a letter informing you of yet another set of publication dates on which we requested the CODRell Gazette publish. That notice of proposed modified BFEs was at last published on April 5, 1989, and April 12, 1989. Therefore, the period for comments or appeals began on April 12, 1989, and ended on July 11, 1989. However, we will delay the finalization of the preliminary FIS and FIRM and the establishment \of an effective date, until we have evaluated any data received within the next 30 days. If we have received no data by the end of this 30 -day period, the preliminary FIS and FIRM will be finalized and the effective date will be established at that time. 2 Should you have any questions regarding this matter, please do not hesitate to contact the Chief, Natural and Technological Hazards Division of the Federal Emergency Management Agency in Denton, Texas,. at (817) 898 -9127 or Matthew B. Miller of our Headquarters staff in Washington, D.C., at (202) 646 -3461. Sincerely, t*e Matticks Risk Studies Division Federal Insurance Administration cc: /Mr. Russell R. Doyle, P.E. Federal Emergency Management Agency CERTIFIED MAIL RETURN RECEIPT REQUESTED Mr. Russell R. Doyle, P.E. City Engineer City of Coppell P.O. Box 478 Coppell, Texas 75019 Washington, C. 20472 July 20, ;r 2 Q g 9 v y f IA- RA- RS(175B): RE: Flood Insurance Study for the City of Coppell, Dallas County, Texas Dear Mr. Doyle: This is to acknowledge receipt of your letter of comment concerning the Federal Emergency Management Agency's (FEMA's) proposed Flood Insurance Study and Flood Insurance Rate Map of your community. The information contained in the letter has been forwarded to FEMA's engineering contractor for evaluation. A representative of the engineering contractor will be contacting you in the near future in reference to the letter of comment. Sincerely, h L. t Matticks C ' f, Risk Studies Division Federal Insurance Administration cc: The Honorable Lou Duggan, Mayor of the City of Mr. Dan M. Dowdey, P.E., Roberts & Dowdey Ms. Shohre Daneshmand, Civil Engineer, City of FEMA, Region VI Texas Water Commission • Coppell Coppell �v���t1GY MggRCct' Federal Emergency Management Agency Washington, D.C. 20472 R 2 C , 0 0 JUL 3 1989 JUJ ? ,1�v 9 The Honorable Lou Duggan Community: City of Copperr,L c : Mayor of the City of Coppell Dallas and DeUO&V- Horn &As:oa. P.O. Box 478 Counties, Texag"1 ", f'"a` Coppell, Texas 75019 Community No.: 480170 Dear Mayor Duggan: This is in reference to a January 12, 1989 letter from Mr. Russell R. Doyle, P.E., City Engineer and Floodplain Administrator for the City of Coppell, in which he requested that the Federal Emergency Management Agency (FEMA) revise the September 22, 1988 preliminary Flood Insurance Study (FIS) and Flood T p (FIRM) for the City of Coppell to include updated corporate insurance Rate Ma limits information and the results of an untitled technical report prepared by Kimley -Horn and Associates, Inc., consulting engineers for the City of Coppell. This report, transmitted to the City of Coppell by Kimley -Horn and Associates, Inc., with a January 5, 1989 letter, contained the following: HEC -2 hydraulic modeling representing the 100- and 500 -year floods and the 100 -year floodway for the Elm Fork of the Trinity River, Grapevine Creek, Denton Creek, and Cottonwood Branch; and topographic mapping of the entire community delineating the proposed 100- and 500 -year floodplain boundaries and the proposed floodway configuration. We have reviewed the submitted technical data for each stream and have identified a number of concerns, enclosed separately as review comments, that must be resolved before FEMA will revise the preliminary FIS and FIRM for the City of Coppell. Please direct all responses to these review comments to our technical evaluation contractor, Dewberry & Davis, 8401 Arlington Boulevard, Fairfax, Virginia 22031, to the attention of Mr. Dave Lushbaugh, Management Engineering and Technical Services Division. Our processing of this request to revise the preliminary FIS and FIRM for your community will be considered inactive pending receipt of your community's response to the review comments. Should you have any questions regarding this matter, please do not hesitate to contact the Chief, Natural and Technological .Iazards Division of the Federal Emergency Management Agency in Denton, Texas, at (817) 898 -9127 or Matthew B. Miller of our Headquarters staff in Washington, D.C., at (202) 646 -3461. Sincerely, J g*, . Matticks C Risk Studies Division Federal Insurance Administration Enclosure cc: Mr. Russell R. Doyle, P.E. ✓ Mr. Ronald Morrison, P.E., Kimley -Horn and Associates, Inc. Mr. Jerry Parch6, P.E., Jerry Parch6 Consulting Engineers City of Coppell, Texas Map Revision Review Comments 1. The submitted HEC -2 hydraulic models did not analyze the 10- and 50 -year floods for each stream. Since this will result in the deletion of these profiles from the Flood Insurance Study (FIS) and would deviate from standard Federal Emergency Management Agency (FEMA) guidelines, please verify whether or not this was your intended course of action. If not, please provide HEC -2 models representing the 10- and 50 -year floods. 2. In a technical report previously submitted to FEMA, entitled Floodplain Hydraulics Study Grapevine Creek Moore Road Bridge Replacement. City of Coppell. Texas, dated 1987, prepared by Kimley -Horn and Associates, Inc., the HEC -2 hydraulic model for Grapevine Creek contains more detailed information than t:e HEC -2 hydraulic model submitted with this request. Specifically, the previous model contains more detailed bridge geometry for the Beltline Road bridge, the most downstream St. Louis Southwestern Railway bridge, and the Moore Road bridge, as well as eleven additional cross sections between cross sections 18650 and 25086. We feel that the more detailed HEC -2 hydraulic model should be used. Please revise the submitted model or justify its use in place of the previously submitted model. 3. The starting water- surface elevations for Grapevine Creek and Denton Creek were determined using the HEC -2 tributary option. This option should be used only when two streams are subject to coincidental peak flooding conditions which normally occurs only with streams of equal drainage area. Please either justify the use of this option or use the slope -area method for the starting water - surface elevation, which may be more applicable to this modeling situation. Please note that when determining the floodway configuration, the effects of backwater flooding from the Elm Fork of the Trinity River should not be included. The tributary option does include the effects of backwater flooding and thus the floodway models should be revised, as appropriate. 4. We have received a request for a conditional Letter of Map Revision for the construction of the proposed Parkway Boulevard bridge, which is located near the confluence of Cottonwood Branch and Denton Creek. This February 24, 1989 request was also from Mr. Doyle and was transmitted to us by our Region VI office. With this request, Mr. Doyle submitted a technical report prepared by Jerry Parche Consulting Engineers that included the following: HEC -2 hydraulic models representing existing and proposed 100 -year flood and floodway conditions for Denton Creek and Cottonwood Branch; topographic mapping delineating the proposed 100 -year floodplain boundary and proposed floodway configuration; and plotted cross sections for Denton Creek and Cottonwood Branch. A comparison of the existing conditions hydraulic models for Cottonwood Branch and Denton Creek from this submittal and the hydraulic models from the Kimley -Horn and Associates, Inc., submittal indicates differences in the technical analyses that yield different results. These differences are listed below. 74 a. Kimley -Horn and Associates, Inc., has modeled the two streams with an assumed common floodplain from their confluence upstream to a point approximately 1,220 feet upstream of Denton Tap Road. Jerry Parch6 Consulting Engineers has modeled the two streams with an assumed common floodplain from their confluence upstream to a point approximately 475 feet upstream of Denton Tap Road. b. The 100 -year flood discharges utilized in the submitted HEC -2 hydraulic models for Denton Creek are outlined below. 100 -Year Flood Discharges Kimley -Horn and I Jerry Parch6 Cross Section Associates, Inc. Consulting Engineers 28870 (below Cottonwood 21300 - - - -- Branch) 32150 21300 21300 32780 (above Cottonwood 21300 21300 Branch) 33145 21300 14900 36970 15600 14900 39440 (at Interstate Route 15600 15600 121) 39540 15400 - - - -- Please note that the flood discharges listed above are for the 100 -year frequency storm only and that there may be similar discrepancies in the 10 -, 50 -, and 500 -year frequency storms. Before FEMA will revise the preliminary FIS and Flood Insurance Rate Map for the City of Coppell, these concerns with Denton Creek and Cottonwood Branch must be resolved. The City of Coppell must resolve these discrepancies and decide upon a single HEC -2 hydraulic model for Denton Creek and for Cottonwood Branch that most accurately represents the floodplain and floodway configura- tion for Denton Creek and Cottonwood Branch for *_heir entire lengths within the community. MA Federal Emergency Management Washington, D.C. 20472 JUL 3 1989 Mr. Jerry Parch6 Jerry Parch6 Consulting Engineers 320 Westway Place, Suite 501 Arlington, Texas 76018 Dear Mr. Parch6: P<_Orl Agenc JUL 0 3 1989 Onley-Harn & Assoo, EM1186, i"AS Case No.: 89-06-31R Community: City of Coppell, Dallas and Denton Counties, Texas Community No.: 480170 This is in reference to a February 24, 1989 letter from Mr. Russell R. Doyle, P.E., City Engineer and Floodplain Administrator for the City of Coppell, in which lie requested, on your behalf, that the Federal Emergency Management 01 Agency (FERA) issue a conditional Letter of Map Revision (LOMR) for the proposed Parkway Boulevard bridge located near the confluence of Cottonwood Branch and Denton Creek. With his letter, which was forwarded to us by our Region VI office, Mr. Doyle submitted a technical report prepared by your firm, entitled Floodplain Reclamation Study on Cottonwood Branch and Denton Creek for Floo�plain Reclamation and Construction of Parkway Boulevard Bridge, dated February 1989. This report contained the following: HEC-2 hydraulic models representing existing and proposed 100-year flood and floodway condi- tions for Denton Creek and Cottonwood Branch; topographic mapping delineating the proposed 100-year floodplain boundary and the proposed floodway configura- tion; and plotted cross sections for Denton Creek and Cottonwood Branch. Please note that we have also received a January 12, Mr. Doyle, in which he requested that FEMA revise th, Insurance Study and Flood Insurance Rate Map for the include updated corporate limits information and the report prepared by Kimley-Horn and Associates, Inc., the City of Coppell. 1989 letter from a September 22, 1988 Flood City of Coppell to results of a technical consulting engineers for A comparison of the hydraulic models for Cottonwood Branch and Denton Creek from your submittal and those from the Kimley-Horn and Associates, Inc., submittal indicates differences in the technical analyses that yield different results. These differences are listed below. 1. Kimley-Horn and Associates, Inc., has modeled the two streams with an assumed common floodplain from their confluence upstream to a point approximately 1,220 feet upstream of Denton Tap Road. Your submittal models the two streams as having an assumed common floodplain from their confluence upstream to a point approximately 475 feet upstream of Denton Tap Road. 2. The 100-year flood discharges utilized in the submitted HEC-2 hydraulic models for Denton Creek are outlined below. 2 Cross Section 28870 (below Cottonwood Branch) 32150 32780 (above Cottonwood Branch) 33145 36970 39440 (at Interstate Route 121) 39540 100 -year Flood Discharges Kimley -Horn and Jerry Parche Associates, Inc. Consulting Engineers 21300 - - - -- 21300 21300 21300 21300 21300 14900 15600 14900 15600 15600 15400 - - - -- Please note that the flood discharges listed above are for the 100 -year frequency storm only and that there may be similar discrepancies in the 10 -, 50 -, and 500 -year frequency storms. Also note that the resolution to these differences should be coordinated with Kimley -Horn and Associates, Inc., and the City of Coppell so that a single HEC -2 hydraulic model for Denton Creek and for Cottonwood Branch will result. Please forward your response along with any supportive technical data to our technical evaluation contractor, Dewberry & Davis, 8401 Arlington Boulevard, Fairfax, Virginia 22031, to the attention of Mr. Dave Lushbaugh, Management Engineering and Technical Services Division. Our processing of this request will be considered inactive until the aforementioned differences are resolved. Please note that if a complete resolution is not received within 90 days of the date of this letter, this case will be treated as an original submittal and will be subject to all submittal /payment procedures including the initial fee. Should you have any questions regarding this matter, please do not hesitate to contact the Chief, Natural and Technological Hazards Division of the Federal Emergency Management Agency in Denton, Texas, at (817) 898 -9127 or Matthew B. Miller of our Headquarters staff in Washington, D.C., at (202) 646 -3461. Sincerely, J hn Matticks Ch Risk Studies Division Federal Insurance Administration cc: Mr. Russell R. Doyle, P.E. ✓ Mr. Ronald Morrison, P.E., Kimley -Horn and Associates, Inc.