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HomeMy WebLinkAboutFDP202000005 Review Comments Appeal to BOS 2020-08-20NATIONAL FLOOD INSURANCE PROGRAM FEMA PRODUCTION AND TECHNICAL SERVICES CONTRACTOR Mr. Jim Taggart, P.E. Director of Engineering Roudabush, Gale & Associates 999 Second Street SE, Suite 201 Charlottesville, VA 22902 Dear Mr. Taggart: August 14, 2020 IN REPLY REFER TO: Case No.: 20-03-1246P Community: Unincorporated Areas of Albemarle County, VA Community No.: 510006 This responds to your request dated May 29, 2020, that the Department of Homeland Security's Federal Emergency Management Agency (FEMA) issue a revision to the Flood Insurance Rate Map (FIRM) for Albemarle County, Virginia, and Incorporated Areas. Pertinent information about the request is listed below. Identifier: Red Hill Quarry Floodplain Flooding Sources: North Fork Hardware River and Unnamed Tributary to North Fork Hardware River FIRM Panel Affected: 51003CO405D The data required to complete our review, which must be submitted within 90 days of the date of this letter, are listed on the attached summary. If we do not receive the required data within 90 days, we will suspend our processing of your request. Any data submitted after 90 days will be treated as an original submittal. FEMA receives a very large volume of requests and cannot maintain inactive requests for an indefinite period of time. Therefore, we are unable to grant extensions for the submission of required data/fee for revision requests. If a requester is informed by letter that additional data are required to complete our review of a request, the data/fee must be submitted within 90 days of the date of the letter. LOMC Clearinghouse, 3601 Eisenhower Avenue, Suite 500, Alexandria, VA 22304 / PH: 1-877-FEMA MAP Compass, under contract with the Federal Emergency Management Agency, is a Production and Technical Services provider for the National Flood Insurance Program Page 2 of 2 If you have general questions about your request, FEMA policy, or the National Flood Insurance Program, please contact the FEMA Map Information eXchange (FMIX), toll free, at 1-877-FEMA MAP (1-877-336-2627). If you have specific questions concerning your request, please contact your case reviewer, Mr. Wade Godman, by e-mail at godmanwg@cdmsmith.com or by telephone at (303) 383- 2372, or the Revisions Coordinator for your state, Ms. Ellie Pitney, by e-mail at pitneyej@cdmsmith.com or by telephone at (303) 383-2318. Sincerely, Benjamin Kaiser, P.E., CFM Revisions Manager Compass PTSJV Attachments: Summary of Additional Data Legal Notice Templates cc: Mr. Frank Pohl, P.E., CFM Floodplain Administrator/County Engineer Albemarle County Mr. Alexander Flint Roudabush, Gale & Associates 316-AD Case No.: 20-03-1246P NATIONAL FLOOD INSURANCE PROGRAM Case No.: 20-03-1246P FEMA PRODUCTION AND TECHNICAL SERVICES CONTRACTOR Summary of Additional Data Required to Support a Letter of Map Revision (LOMR) Requester: Mr. Jim Taggart, P.E. Community: Unincorporated Areas of Albemarle Community No.: 510006 County, VA The issues listed below must be addressed before we can continue the review of your request. 1. Our review revealed that the second signature block on the online Letter of Map Change (LOMC) application form was not signed by the Albemarle County official. Please submit the online application summary page again with the Albemarle County official signature included. If MT-2 Form 1, entitled "Overview and Concurrence Form" will be submitted then ensure that all three signature blocks in Section D have been signed. All forms and instructions are available for your information on the FEMA website at hMs://www.fema.gov/library/viewRecord.do?id=1493. 2. Our review revealed that a hydrologic analysis was not submitted for North Fork Hardware River. Please send us the hydrology used to develop the discharges in the HEC-RAS hydraulic model and all necessary backup information, including a certified drainage area map, land use and soils information, and time of concentration calculations. Please include clearly labeled contours, time of concentration calculations, and soil and land use characteristics. Please refer to https://www. fema. gov/hydrologic-models-meeting-minimum-requirement-national-flood-insurance- program to view "Hydrologic Models Meeting the Minimum Requirements of the National Flood Insurance Program," and submit a hydrologic analysis using one of these FEMA-accepted approaches. 3. Our review of the submitted HEC-HMS 4.3 hydrologic model along Unnamed Tributary to North Fork Hardware River revealed the following issues. Please submit a revised hydrologic analysis that corrects these issues and provide digital copies of the input and output files for this model. a. Our review revealed the pond at the upstream end of the Unnamed Tributary to North Fork Hardware River is not included in the hydrologic model. Please submit a revised hydrologic analysis that includes the pond and provide an explanation if the pond is controlling the flows in the watershed. If the pond is controlling flow, please provide an Operations and Maintenance plan for the pond and an explanation that it is dedicated to flood storage. b. Please provide supporting information for the percent impervious value used in the hydrologic analysis. 4. Our review of the HEC-HMS hydrologic model and HEC-RAS hydraulic model revealed the discharge value of 680.2 cubic feet per second (cfs) used along the Unnamed Tributary to North Fork Hardware River in the HEC-RAS model is not supported by the hydrologic analysis. If the intent is to have a flow change location along the flooding source, please split the watershed in the HEC-HMS model into multiple sub basins. Please correct the appropriate files to ensure the models are consistent and provide the revised files. LOMC Clearinghouse, 3601 Eisenhower Avenue, Suite 500, Alexandria, VA 22304 / PH: 1-877-FEMA MAP Compass, under contract with the Federal Emergency Management Agency, is a Production and Technical Services provider for the National Flood Insurance Program Page 2 of 4 5. Our review of the submitted existing conditions Hydrologic Engineering Center's River Analysis System HEC-RAS 5.0.7 hydraulic analysis revealed the following issues. Please submit a revised hydraulic analysis that corrects these issues and provide digital copies of the input and output files for this model. a. Our review revealed that the HEC-RAS model uses the junction option as the downstream boundary condition for the Unnamed Tributary to North Fork Hardware River. Please remove all junctions from the submitted hydraulic model. This option should only be used if the tributary and main stream have coincident peaks. Please model the tributary independent of North Fork Hardware River, using normal depth (i.e., the slope -area method) as the downstream boundary condition, or provide engineering data and calculations to support a coincident peak with North Fork Hardware River. Please be certain to use the backwater effects of the North Fork Hardware River to map the confluence. b. Our review revealed the Unnamed Tributary to North Fork Hardware River crosses Red Hill Road near the confluence with North Fork Hardware River. Please revise the model to include the structure at Red Hill Road or provide an explanation as to why this is not necessary. If modeled, please provide certified as -built plans or certified survey plans to verify the inverts and dimensions of the structures and road elevations used in the model. Please also ensure that the Structure sections 2 and 3 are placed appropriately as per the HEC-RAS Hydraulics Reference Manual and contraction and expansion coefficients are updated as per the manual. Additionally, please fill out and submit Form 3, entitled "Riverine Structures Form." All forms and instructions are available for your information on the FEMA website at hfts://www.fema.gov/libLW/viewRecord.do?id=1493. c. Our review revealed that a levee condition exists on the right overbank of Cross Section 3659 along the Unnamed Tributary to North Fork Hardware River. Please provide an explanation that the high -ground is naturally occurring and that the low -ground is not hydraulically connected to the main floodplain or map the area behind the high -ground as being inundated by the base flood. If the levee condition is due to man-made conditions (i.e., fill placed in the floodplain), then the project must meet all parts of Section 65.10 of the NFIP regulations in order to provide protection from the base flood. d. In the submitted HEC-RAS model one profile entitled " PFI" is included. For clarity, please rename the profile to have a descriptive and clear name such as "100-yr." e. An ineffective flow area is defined as the area of a cross section that will contain water that is not actively being conveyed. It is used to describe portions of a cross section in which water will pond, but the velocity in the downstream direction is close to zero. Our review of the submitted existing conditions hydraulic analysis revealed that ineffective flow should be used at Cross Sections 3887 and 1233 along North Fork Hardware River and Cross Section 3659 along the Unnamed Tributary to North Fork Hardware River. Please revise the submitted HEC-RAS model at the above -mentioned cross sections to account for ineffective flow areas, or provide an explanation why this is not necessary. f Our review of the submitted hydraulic analysis revealed a hydraulic jump in the 1-percent- annual-chance (base) water -surface elevation (WSEL) along North Fork Hardware River from Cross Section 1552 to 1233. Please revise the submitted model to remove this hydraulic jump or provide an explanation why this cannot be removed. . g. Our review of the submitted hydraulic analyses revealed numerous locations of excessive reach 316-AD Case No.: 20-03-1246P Page 3 of 4 length between modeled cross sections along the Unnamed Tributary and North Fork Hardware River. Additional cross sections in the hydraulic models may be appropriate to more accurately analyze the WSELs at these locations. Please add additional cross sections between cross sections with reach lengths exceeding 500 feet, or explain why this is not necessary. h. Our review revealed WSELs higher than the end points of Cross Sections 3818, 3659, and from Cross Section 178 to Cross Section 32 in the submitted existing conditions hydraulic model along the Unnamed Tributary to North Fork Hardware River. Please revise the cross section geometry coordinates so that the end points of all cross sections are equal to, or extend higher than, the corresponding WSELs. Please ensure the cross sections near the confluence are oriented appropriately so that they do not intersect one another or with any cross section of North Fork Hardware River within the revised base floodplain delineation. i. Our review revealed a consistent Manning's "n" across each cross section in the existing conditions hydraulic model and do not appear to be indicative of natural conditions. Typically, the overbank values are higher than the channel, please provide justification for the same n values used along the overbanks of Unnamed Tributary to North Fork Hardware River and North Fork Hardware River as the channel or revise the model as appropriate. 6. The submitted topographic work map, entitled "Certified Topographic Work Map," prepared by Roudabush, Gale & Associates, Inc., dated May 5, 2020, does not provide some of the essential information required to complete our review of this request. Please submit a revised topographic work map, certified by a registered Professional Engineer (P.E.), that shows all applicable items listed in Section C of Application/Certification Form 2, entitled "Riverine Hydrology and Hydraulics Form," including the following information: a. Please clearly label the topographic contours close to the revised floodplain delineation to ensure the delineations can be easily verified. b. Please ensure that the cross section labels shown on the work map are consistent with the cross section labeled in the submitted existing conditions hydraulic model along both flooding sources. c. Please ensure to update the base floodplain at the confluence based on the backwater elevation from the North Fork Hardware River along Unnamed Tributary to North Fork Hardware River until the hydraulic model elevation is higher than the backwater elevation. d. The revised floodplain topwidths and reach lengths were not able to be verified on the above referenced work map at all cross sections. Please revise the above -referenced work map to show the cross sections and streamline more clearly. It is recommended to use different colored lines for the cross sections, topography, base floodplain delineation, and streamline. Please do not show the effective or revised floodplain as shading/hatching. Please show them in different line type and color to easily distinguish between them. e. Our review revealed the revised base floodplain does not adequately tie-in to the effective floodplain at the upstream and downstream end of North Fork Hardware River. Please show logical tie-ins between the revised and effective flood hazard boundary delineations at the upstream and downstream ends of the revision area. The upstream graphical tie-in should be upstream of the upstream -most cross section within the revision area where vertical tie-in is achieved, and the downstream graphical tie-in should be downstream of the downstream -most cross section within the revision area. f. Please ensure consistency between the information presented on the work map and in the 316-AD Case No.: 20-03-1246P Page 4 of 4 hydraulic models, including the following: i. The geometry used in the hydraulic models should match the topography shown on the work map. ii. The topwidths of the delineated floodplain should match those computed in the hydraulic models. iii. The distance between cross sections measured along the channel flow line on the work map matches the Downstream Reach Lengths used in the HEC-RAS hydraulic models. To aid in accuracy and to expedite the mapping process, please provide Geographic Information System (GIS) data along with the certified topographic work map submittal. If this is not available, please provide digital Computer -Aided Design (CAD) along with the work map. Please ensure the digital data is spatially referenced and cite what projection (coordinate system, example: UTM/State Plane) was used. The important data to show on the digital work map are the contour information, the stream centerline, the cross section lines, the effective and revised flood hazard delineations and the tie-in locations. Everything should be clearly labeled, and all information should be contained within the drawing and not externally referenced. 8. Please submit annotated FIRM panels that are consistent with the changes requested in the items above. 9. Please submit a copy of the newspaper notice distributed by Albemarle County stating their intent to revise or establish the flood hazard information (i.e., base flood elevations/base flood depths, and base flood floodplain) along North Fork Broad Run and the unnamed tributary to North Fork Broad Run, or submit documentation that individual legal notices were sent to all the property owners affected by any increases in or establishment of flood hazard information. Documentation of legal notice may take the form of a copy of the letter sent along with certified mailing receipts or a mailing list. The newspaper notice or individual legal notices must include contact information for any interested parties. Please submit a draft copy of the notification for verification of content, prior to publication or distribution. The attached templates may be used to prepare the draft notification. 10. To support the waived fee for this LOMR, please provide supporting documentation that demonstrates no man-made changes have been made in the floodplain since the effective FIRM panel dated December 16, 1980. If man-made changes such as fill placement or any new bridge/culvert modeling have been made to the floodplain since the date of the FIRM published for this flooding source, please submit a fee in accordance with the fee schedule on the FEMA website at hfts://www.fema.gov/plWpreventtfbm/frm fees.shtm. Please send the required data directly to your case reviewer via email/FTP. Alternatively, please upload the required data using the Online LOMC website. https://hazards.fema.gov/femqportal/onlinelomc/signin. For identification purposes, please include the case number referenced above on all correspondence. 316-AD Case No.: 20-03-1246P