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Guidance for Flood Risk Analysis and Mapping

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Guidance for Flood Risk Analysis and Mapping Guidance for Flood Risk Analysis and Mapping Levees December 2020 Requirements for the Federal Emergency Management Agency (FEMA) Risk Mapping, Assessment, and Planning (Risk MAP) Program are specified separately by statute, regulation, or FEMA policy (primarily the Standards for Flood Risk Analysis and Mapping). This document provides guidance to support the requirements and recommends approaches for effective and efficient implementation. The guidance, context, and other information in this document is not required unless it is codified separately in the aforementioned statute, regulation, or policy. Alternate approaches that comply with all requirements are acceptable. For more information, please visit the FEMA Guidelines and Standards for Flood Risk Analysis and Mapping webpage (www.fema.gov/flood-maps/guidance-partners/guidelines-standards). Copies of the Standards for Flood Risk Analysis and Mapping policy, related guidance, technical references, and other information about the guidelines and standards development process are all available here. You can also search directly by document title at www.fema.gov/multimedia- library. Levees December 2020 Guidance Document 95 Page i Table of Revisions The following summary of changes details revisions to this document subsequent to its most recent version in November 2019. Affected Section or Date Description Subsection December Section 1.2.4, 1.2.5 Corrected minor alignment of wording. 2020 December Added more details to describe the National Levee Safety Section 1.3.1 2020 Program. December Section 4.1.10.2 Updated web links. 2020 Section 4.2 and December Updated to reflect FEMA and USACE data sharing processes. subsections 2020 Section 4.4, 6.12, and December Minor wording revisions to address revised standards and 6.19 2020 introduction of evaluation lines for 2-D based floodways. December Section 5.5.2 Corrected expiring PAL guidance to align with new standard. 2020 December Section 6.19 Updated Zone D information and minor alignment of wording. 2020 December Added text for inclusion into the FIS when Freeboard Deficient Section 6.21.1 2020 approach is used and when Zone D is used. Levees December 2020 Guidance Document 95 Page ii Table of Contents 1.0 Levees Overview ................................................................................................................ 1 1.1 Prior Guidance Documents ............................................................................................ 2 1.2 Flood Hazard Mapping and Levees ................................................................................ 2 1.3 Summary of Recent Legislation and Recommendations ................................................ 5 1.4 Levee-Related Communication and Community Engagement ....................................... 6 1.5 Chapter Overviews ......................................................................................................... 7 2.0 Glossary ............................................................................................................................. 9 3.0 Levee Data Inventory ....................................................................................................... 16 3.1 Background .................................................................................................................. 16 3.2 National Levee Database ............................................................................................. 17 3.3 Identification and Mapping of Levees in Flood Hazard Studies and Map Revisions .... 17 3.4 FEMA Regulatory Levee Data ...................................................................................... 19 3.5 Tracking Levee Accreditation Status ............................................................................ 20 3.6 Reporting Levee System Updates ................................................................................ 20 3.7 Levee Data Storage Standards .................................................................................... 21 4.0 Accredited Levee Systems ............................................................................................... 22 4.1 44 CFR 65.10 Requirements ........................................................................................ 24 4.2 Additional Levee Accreditation Considerations ............................................................ 37 4.3 Levee Accreditation Reviews ....................................................................................... 46 4.4 Accredited Levee Mapping and Notes .......................................................................... 52 5.0 Provisionally Accredited Levee Systems ......................................................................... 55 5.1 Provisional Levee Accreditation Overview ................................................................... 55 5.2 PAL Eligibility Requirements ........................................................................................ 56 5.3 Considerations for Offering PAL to PAL Eligible Levee Systems ................................. 57 5.4 PAL Communication and Coordination Processes ....................................................... 60 5.5 PAL Mapping and Notes ............................................................................................... 66 6.0 Non-Accredited Levee Systems ....................................................................................... 67 6.1 Non-Accredited Levee Systems Defined ...................................................................... 67 6.2 Other Considerations .................................................................................................... 68 6.3 Levee Analysis and Mapping Procedure ...................................................................... 69 6.4 Levee Data Collection and Stakeholder Engagement (Figure 11, Element 200) ......... 72 Levees December 2020 Guidance Document 95 Page iii 6.5 Local Levee Partnership Team (Figure 11, Element 300) ............................................ 80 6.6 Local Levee Partnership Team Meetings (Figure 11, Element 300) ............................ 82 6.7 Levee Analysis and Mapping Plan (Figure 11, Element 400) ....................................... 84 6.8 Additional Data Collection (Figure 11, Element 410) .................................................... 85 6.9 System-Wide Analysis and Mapping Procedures (Figure 11, Element 610) ................ 86 6.10 Levee Reach Analysis and Mapping Procedures (Figure 11, Element 620) ................ 88 6.11 Natural Valley Procedure (Figure 11, Element 620) ..................................................... 90 6.12 Structural-Based Inundation Procedure (Figure 11, Element 620) ............................... 94 6.13 Overtopping Procedure (Figure 11, Element 620) ...................................................... 100 6.14 Freeboard Deficient Procedures (Figure 11, Element 620) ........................................ 105 6.15 Sound Reach Procedure (Figure 11, Element 620) ................................................... 106 6.16 Flood Hazards Evaluated by Flooding Source (Figure 11, Element 630)................... 108 6.17 Hydrograph Development ........................................................................................... 108 6.18 Regulatory Floodways ................................................................................................ 112 6.19 Hydraulic Modeling on Landside of the Levee ............................................................ 123 6.20 Flood Hazard Mapping ............................................................................................... 126 6.21 Guidance Regarding Flood Insurance Study Report Standards ................................ 130 6.22 Documentation ........................................................................................................... 132 6.23 Review Procedures .................................................................................................... 132 7.0 Non-Levee Reaches and Non-Levee Features .............................................................. 134 7.1 Non-Levee Reach ....................................................................................................... 135 7.2 Non-Levee Features ................................................................................................... 136 7.3 Communication of Risk ............................................................................................... 137 8.0 FEMA and Other Federal Agency Coordination ............................................................. 138 8.1 USACE ....................................................................................................................... 138 List of Figures Figure 1: Example Levee System A ............................................................................................ 23 Figure 2: Freeboard Determination ............................................................................................. 26 Figure 3: Freeboard Near Structures .......................................................................................... 26 Figure 4: Wave Runup ................................................................................................................ 29 Figure 5: Levee System Designed to End in the Absence of High Ground ................................ 38 Levees December 2020 Guidance Document 95 Page iv Figure 6: Levee System Tying into Non-Levee Reach ..............................................................
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