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FIRM-920317 (2)�NGY MAN �'�G gcF3 Q a Federal Emergency Management Agency Washington, D.C. 20472 -, MAR 17 1992 Mr. Dan M. Dowdey, P.E. .4, ,,,,Ago Dan M. Dowdey and Associates, Inc. 6250 Dallas Parkway, Suite 100 Dallas, Texas 75248 Dear Mr. Dowdey: S Community: City of Coppell, Dallas and Denton, Counties, Texas Community No.: 480170 This is in response to your January 16, 1992, letter commenting on the December 18, 1991, preliminary revised Flood Insurance Study (FIS) and Flood Insurance Rate Map (FIRM) for the City of Coppell, Texas. In your January 16, 1992, letter, you stated that topographic surveys conducted by your firm indicate that the 100 -year floodplain for Denton Creek should be revised on the southwest bank in the vicinity of Village Parkway. With your letter, you submitted an annotated portion of the preliminary FIRM depicting the revised 100 -year floodplain based on the topographic survey, but topographic informa- tion was not submitted to support the revised floodplain boundary. The floodplain boundaries depicted on the December 18, 1991, preliminary FIRM for the City of Coppell were based on topographic mapping submitted by Morrison Hydrology /Engineering, Inc., and Kimley -Horn Associates, Inc., in support of a comprehensive restudy of flood hazards within the City of Coppell. This restudy, which was the primary basis for the December 18, 1991, preliminary revised FIRM, was prepared on behalf of the City of Coppell to best represent currently existing conditions and was submitted to the Federal Emergency Management Agency (FEMA) as such. Before the floodplain boundaries for Denton Creek on the preliminary FIRM for Coppell can be revised in the area of concern, topographic mapping certified by a registered professional engineer or licensed land surveyor must be submitted to justify the revised floodplain boundary delineation. In addition, if fill has been placed in the area of cnnrern, the data require- ments for fill compaction, as outlined in Subparagraph 65.5(a)(6) of the National Flood Insurance Program regulations (copy enclosed), must be met. For your convenience, we have enclosed a form entitled Certification of Fill Compaction, which can be used to certify the aforementioned fill requirements. We are continuing our processing of the preliminary revised FIS and FIRM for the City of Coppell and will soon initiate the 90 -day appeal period. However, if the aforementioned required data are submitted in a timely fashion, the revised floodplain boundary delineation for Denton Creek in the area of concern will be incorporated into the final published FIRM, if technically appropriate. 2 Please submit the required data within 30 days of the date of this letter directly to our technical evaluation contractor at the following address: Mr. Joseph B. Chapman Dewberry & Davis Management Engineering and Technical Services Division 8401 Arlington Boulevard Fairfax, Virginia 22031 We thank you for your review of the City of Coppell's preliminary revised FIS and FIRM. Should you have any questions regarding this matter, please do not hesitate to contact the Chief, Natural and Technological Hazards Division of FEMA in Denton, Texas, at (817) 898 -5127 or Matthew B. Miller of our Headquarters staff in Washington, D.C., at (202) 646 -3461. Sincerely, William R. Locke Chief, Risk Studies Division Federal Insurance Administration Enclosures cc: The Honorable Mark Wolfe, Mayor of the City of Coppell Mr. Ken Griffin, P.E., City Engineer Mr. Ron Morrison, P.E., Morrison Hydrology /Engineering, Inc. § 65.4 § 65.4 Right to submit new technical data (a) A community has a right to re- quest changes to any of the informa- tion shown on an effective map that does not impact flood plain or flood - way delineations, or base flood eleva- tions, such as community boundary changes, labeling, or planimetric de- tails. Such a submission shall include appropriate supporting documentation in accordance with this part and may be submitted at any time. (b) All requests for changes to effec- tive maps, other than those initiated by FEMA, must be made in writing by the Chief Executive Officer of the community (CEO) or an official desig- nated by the CEO. Should the CEO refuse to submit such a request on behalf of another party, FEMA will agree to review it only if written evi- dence is provided indicating the CEO or designee has been requested to do SO. 151 FR 30313, Aug. 25, 19861 65.5 Revision to special hazard area boundaries with no change to base flood elevation determinations. (a) Data requirements for topograph- ic changes. In many areas of special flood hazard (excluding V zones and floodways) it may be feasible to ele- vate areas with earth fill above the base flood elevation. Scientific and technical information to support a re- quest to gain exclusion from an area of special flood hazard of a structure or parcel of land that has been elevat- ed by the placement of fill shall in- clude the following (1) A. copy of the recorded deed indi- cating the legal description of the property and the official recordation information (deed book volume and page number) and bearing the seal of the appropriate recordation official (e.g., County Clerk or Recorder of Deeds). (2) If the property is recorded on a Plat map, a copy of the recorded plat indicating both the location of the property and the official recordation information (plat book volume and page number) and bearing the seal of the appropriate recordation official. If the property is not recorded on a plat map, copies of the tax map or other 44 CFR Ch. 1 (14 -1 -88 Edition) suitable maps are required to aid FEMA in accurately locating the prop- erty. (3) If a legally defined parcel of land is involved, a topographic map indicat- ing present ground elevations and date of fill. F'EMA's determination as to whether a legally defined parcel of land is to be excluded from the area of special flood hazard shall be based upon a comparison of the ground ele- vations of the parcel with the eleva- tions of the base flood. If the ground elevations of the entire legally defined Parcel of land are at or above the ele- vations of the base flood, the parcel may be excluded from the area of spe- cial flood hazard. (4) If a structure is involved, a topo- graphic map indicating structure loca- tion and ground elevations including the elevations of the lowest floor (in- cluding basement) and the lowest ad- jacent grade to the structure. FEMA's determination as to whether a struc- ture is to be excluded from the area of special flood hazard shall be based upon a comparison of the elevation of the lowest floor (including basement) and the elevation of the lowest adja- cent grade with the elevation of the base flood. If the entire structure and the lowest adjacent grade are at or above the elevation of the base flood, the structure may be excluded from the area of special flood hazard. (5) Data to substantiate the base flood elevation. If FEMA has complet- ed a Flood Insurance Study (FIS), that data will be used to substantiate the base flood. Otherwise, data provid- ed by an authoritative source, such as the U.S. Army Corps of Engineers, U.S. Geological Survey, U.S. Soil Con- servation Service, state and local water resource departments, or technical data prepared and certified by a regis- tered professional engineer may be submitted. If ' base flood elevations have not previously been established, hydraulic calculations may also be re- quested. (6) Where fill has been placed to raise the ground surface to or above the base flood elevation and the re- quest to gain exclusion from an area of special flood hazard includes more than a single structure or a single lot, It must be demonstrated that fill will 352 Federal Emergency h. agement Agency not settle below the elevation of the base flood, and that the fill is ade- quately protected from the forces of erosion, scour, or differential settle- ment as described below: (D Fill must be compacted to 95 per- cent of the maximum density obtain- able with the Standard Proctor Test method issued by the American Socie- ty for Testing and Materials (ASTM Standard D -698). This requirement applies to fill pads prepared for resi- dential or commercial structure foun- dations and does not apply to filled areas intended for other uses. (ii) Fill slopes for granular materials are not steeper than one vertical on onz -and- one -half horizontal unless substantiating data justifying steeper slopes is submitted. (iii) Adequate protection is provided fill slopes exposed to flood waters with expected velocities during the occur- rence of the base flood of five feet per second or less by covering them with grass, vines, weeds, or similar vegeta- tion undergrowth. (iv) Adequate protection is provided fill slopes exposed to flood waters with velocities during the occurrence of the base flood of greater than five feet per second by armoring them with stone or rock slope protection. (7) A revision of flood plain delinea- tions based on fill must demonstrate that any such fill has not resulted in a floodway encroachment. (b) New topographic data. The pro- cedures described in paragraphs (a) (1) through (5) of this section may be also followed to request a map revision when no physical changes have oc- curred in the area of special flood hazard, when no fill has been placed, and when the natural ground eleva- tions, as evidenced by new topographic maps, more detailed or more accurate than those used to prepare the map to be revised, are shown to be above the elevation of the base flood. (c) CertVication requirements. The items required in paragraphs (a) (3) and (4) and (b) of this section shall be certified by a registered professional engineer or licensed land surveyor. Items required in paragraph (a)(6) of this section shall be certified by the community's NFIP permit official, a registered professional engineer, or an accredited soils engineer. Such certifi- cations are subject to the provisions of § 65.2. of this subchapter. (d) Submission procedures. All re- quests shall be submitted to the appro- priate FEMA Regional Office servicing the community's geographic area. (51 FR 30313, Aug. 25, 19861 353 § 65.6 § 65.6 Revision of base flood elevation de- terminations. (a) General conditions and data re- quirements. (1) The supporting data must include all the information FEMA needs to review and evaluate the request. This may involve the re- questor's performing new hydrologic and hydraulic analysis and delineation of new flood plain boundaries and floodways, as necessary. (2) To avoid discontinuities between the revised and unrevised flood data, the necessary hydrologic and hydrau- lic analyses submitted by the map re- vision requestor must be extensive enough to ensure that a logical transi- tion can be shown between the revised flood elevations, flood plain bound- aries, and floodways and those devel- oped previously for areas not affected by the revision. Unless it is demon- strated that it would not be appropri- ate, the revised and unrevised base flood elevations must match within one -half foot where such transitions occur. .(3) Revisions cannot be made based on the effects of proposed projects or future conditions. Section 65.8 of this subchapter contains provisions for ob- taining conditional approval of pro- posed projects that may effect map changes when they are completed. (4) The datum and date of releveling of benchmarks, if any, to which the elevations are referenced must be indi- cated. (5) Maps will not be revised when discharges change as a result of the use of an alternative methodology or data for computing flood discharges unless the change is statistically sig- nificant as measured by a confidence limits analysis of the new discharge es- timatres. (6) Any computer program used to perform hydrologic or hydraulic analyses in support of a flood insurance map re- vision must meet all of the following criteria: (i) It must have been re- viewed and accepted by a governmental agency responsi- ble for the implementation of programs for flood control and /or the regulation of flood plain lands. For com -. puter programs adopted by non - Federal agencies, certi- fication by a responsible `A Federal Emergency Management Agency Community Washington, D.C. 20472 CERTIFICATION OF FILL COMPACTION Property I hereby certify that fill placed on the property to raise the ground surface to or above the Base (100 -year) Flood Elevation in order to gain exclusion from a Special Flood Hazard Area (100 -year floodplain) meets the criteria of Title 44 of the Code of Federal Regulations, Part 65.5(x)(6), listed below. For proposed fill, I hereby certify that it is designed in accordance with these criteria. Note: Any modifications or additions to this form will render it void. 1. That the fill has been compacted to 95 percent of the maximum density obtainable with the Standard Proctor Test method or an acceptable equivalent method for (check one of the following): a. Fill pads prepared for the foundations of residential or commercial structures. b. Entire legally defined parcel (Note: If the location of fill pads has not been determined, the fill over the entire legally defined parcel must be compacted to the above criteria) 2. That fill slopes for granular materials are not steeper than one vertical on one - and - one -half horizontal (steeper slopes must be justified); and 3. That adequate erosion protection is provided for fill slopes exposed to moving flood waters (Slopes exposed to flows with velocities of up to 5 feet per second (fps) during the 100 -year flood must, at a minimum, be protected by a cover of grass, vines, weeds, or similar vegetation; slopes exposed to flows with velocities greater than 5 fps during the 100 -year flood must, at a minimum, be protected by stone or rock riprap). Signature Date Community Official's Title or Engineer's Seal January 1990