Loading...
Deforest Court-CS000315: ' ,'-- '"-, e. Lo P-.. Federal Emergency Management Agency o.c. HAR 1 5 2000. CERTIFIED MAIL IN REPLY REFER TO: RETURN RECEIPT REQUESTED Case No.: 00-06-276R The Honorable Candy Sheehan Community: City of Coppell, Texas Mayor, City of Coppell Community No.: 480170 255 Parkway Boulevard Coppell, TX 75019 104 Dear Mayor Sbeehan: This responds to a request that the Federal Emergency Management Agency (FEMA) comment on the effects that a proposed project would have on the effective Flood Insurance Rate Map (FIRM) and Flood Insurance Study (FIS) report for your community in accordance with Part 65 of the National Flood Insurance Program (NFIP) regulations. In a letter dated September 24, 1999, Mr. Walter E. Skipwith, P.E., Vice President, Halff Associates, Inc., requested that FEIMA evaluate the effects that proposed placement of fill and proposed excavation of a pond and swale along Denton Creek would have on the flood hazard information shown on the effective FIRM and HS report. The proposed site improvements are associated with the Windsor Estates and DeForest Court subdivisions. This request also included more detailed topographic information to reflect existing watershed conditions along Denton Creek from approximately 4,600 feet downstream of DeForest Road (extended) to approximately 1,620 feet downstream of the convergence of Old Denton Creek. All data required to complete our review of this request for a Conditional Letter of Map Revision (CLOMR) were submitted with letters from Mr. Kenneth M. Griffin, P.E., Director of Public Works, City of Coppell; Mr. T.S. Kumar, P.E., Assistant City Engineer, City of Lewisville; Ms. Nancy S. Cline, P.E., Assistant Director of Public Works, City of Carrollton; Mr. Russell P. Erskine, Hydrologist, Halff Associates, Inc.; and Mr. Skipwith. Because this revision request also affects the Cities of Lewisville and Carrollton, separate CLOMRs for those communities were issued on the same date as this CLOMR. We are processing a revised FIRM and FIS report for Dallas County, Texas and Incorporated Areas in our countywide format. Preliminary copies of the countywide FIRM and FIS report were submitted to your community for review on July 30, 1999. We reviewed the submitted data and the data used to prepare the preliminary FIRM and determined that the proposed project meets the minimum floodplain management criteria of the NFIP. The submitted corrected effective HEC-2 hydraulic computer model, dated September 12, 1999, based on updated topographic information, corrections to the hydraulic modeling for Denton Creek, and the addition of a split-flow analysis at Dallas Gun Club Road, was used as the base conditions model in our review of the proposed conditions model for this CLOMR request. We believe that, if the proposed project is constructed as shown on the submitted topographic work map entitled "Revised (Proposed) Conditions Site Plan, Windsor Estates / DeForest Court," prepared by Halff Associates, Inc., dated September 1999, and the data listed below are received, a revision to the FIRM would be warranted. As a result of the updated topographic information, corrections to the hydraulic modeling for Denton Creek, and oddition of a split-flow analysis at Dallas Gun Club Road, the elevations of the flood having a l-percent chance of being equaled or exceeded in any given year (base flood) increased and decreased compared to the effective base flood elevations (BFEs) for Denton Creek from approximately 4,600 feet downstream of DeForest Road (extended) to approximately 5,800 feet upstream of the convergence of Old Denton Creek. The maximum increase in BFE, 0.9 foot, occurred approximately 880 feet downstream of the convergence of Old Denton Creek. The maximum decrease in BFE, 2.4 feet, occurred approximately 4,600 feet downstream of DeForest Road (extended). The BFEs will decrease compared to the corrected effective BFEs as a result of the proposed placement of fall and excavation of a pond and swale along Denton Creek. The maximum decrease in BFE, 0.1 foot, will occur approximately 1,140 feet upstream of DeForest Road (extended). As a result of the updated topographic information, corrections to the effective model, and proposed project, the BFEs will increase and decrease compared to the effective BFEs for the revised reach of Denton Creek. The maximum increase in BFE, 0.9 foot, will occur approximately 880 feet downstream of the convergence of Old Denton Creek. The widths of the Special Flood Hazard Area (SFHA), the area that would be inundated by the base flood, and the regulatory floodway will increase in some areas and decrease in other areas compared to the SFHA and floodway widths shown on the preliminary countywide FIRM. The minor increases in SFHA width will be contained on property owned by the requester. Upon COmpletion of the project, your community may submit the data listed below and request that we make a f'mal determination on revising the effective FIRM and FIS report. · Effective March 1, 1999, FEMA revised the fee schedule for reviewing and processing requests for conditional and final modifications to published flood information and maps. In accordance with this schedule, the fee for your map revision request will be $3,400 and must be received before we can begin processing your request. Payment of this fee shall be made in the form of a check or money order, made payable in U.S. funds to the National Flood Insurance Program, or by credit card. The payment must be forwarded to the following address: Federal Emergency Management Agency Fee-Collection System Administrator P.O. Box 3173 Merrifield, VA 22116-3173 · As-built plans, certified by a registered professional engineer, of all proposed project elements · Community acknowledgment of the map revision request · Certification that all fill placed in the currently effective base floodplain and below the proposed BFE is compacted to 95 percent of the maximum density obtainable with the Standard Proctor Test method issued by the American Society for Testing and Materials (ASTM Standard D-698) or an acceptable equivalent method for all areas to be removed from the base floodplain · A copy of the public notice distributed by your community stating its intent to revise the regulatory floodway, or a statement by your community that it has notified all affected property owners and affected adjacent jurisdictions · A letter stating that your community will adopt and enforce the modified regulatory floodway · Hydraulic analyses, for as-built conditions, of the base flood; the floods having a 10-, 2-, and 0.2-percent chance of being equaled or exceeded in any given year;, and regulatory floodway if they differ from the proposed conditions models · Our review revealed that the revised BFEs and regulatory floodway will tie into the effective BFEs and floodway within 0.5 foot at Cross Section 28870 in the submitted hydraulic model for Denton Creek. The above-referenced topographic work map includes only cross sections up to and including Cross Section 22370. Please extend the floodplain and floodway boundary delineations shown on the topographic work map to include the cross sections between Cross Sections 23370 and 28870 to illustrate how the revised floodplain and floodway boundary delineations fie into the effective floodplain and floodway boundary delineations at the upstream end of the revised reach along Denton Creek. · Our review of the submitted proposed floodway model revealed that the model ends at Cross Section22370. Please extend the proposed floodway model to include effective Cross Sections 23800 through 28870, so that the floodway model is consistent with the multiple profile model and so that the revised BFEs tie into the effective BFEs within 0.5 foot. Please ensure that the floodway analysis produces maximum surcharges of no more than 1.0 foot throughout the revised reach. After receiving appropriate documentation to show that the project has been completed, FEMA will initiate a revision to the FIRM and FIS report. Because the BFEs would change as a result of the project, a 90-day appeal period would be initiated, during which community officials and interested persons may appeal the revised BFEs based on scientific or technical data. The basis of this CLOMR is, in whole or in part, a channel-modification project. NFIP regulations, as cited in Paragraph 60.3Co)(7), require that communities assure that the flood-carrying capacity within the altered or relocated portion of any watercourse is maintained. This provision is incorporated into your community's existing floodplain management regulations. Consequently, the ultimate responsibility for maintenance of the modified channel rests with your community. This CLOMR is based on minimum floodplain management criteria established under the NFIP. Your community is responsible for approving all floodplain development and for ensuring all necessary permits required by Federal or State law have been received. State, county, and community officials, based on knowledge of local conditions and in the interest of safety, may set higher standards for construction in the SFHA. If the State, county, or community has adopted more restrictive or comprehensive floodplain management criteria, these criteria take precedence over the minimum NFIP criteria. If you have any questions regarding floodplain management regulations for your community or the NFIP in general, please contact the Consultation Coordination Officer (CCO) for your community. Information 4 on the CCO for your community may be obtained by contacting the Director, Mitigation Division of FEMA in Denton, Texas, at (940) 898-5127. If you have any 'questions'regarding this CLOMR, please contact the FEMA Map Assistance Center, toll free, at 1-877-FEMA MAP (1-877-336-2627). Sincerely, Alan A. John~ m,~P.E., Project Engineer For: Matthew B. Miller, P.E., Chief Hazards Stud~~BfanB ch .Hazards Study Branch Mitigation Dir.-'~torate Mitigation Directorate Enclosure cc: The Honorable Milburn Gravley Mayor, City of Carrollton The Honorable Bobby J. Mitchell Mayor, City of Lewisville Mr. Kenneth M. Griffin, P.E. ~/ Director of Public Works City of Coppell Mr. Walter E. Skipwith, P.E. Vice President Halff Associates, Inc. Mr. Russell P. Erskine Hydrologist Halff Associates, Inc.