RIVERINE EROSION HAZARD AREAS Mapping Feasibility Study

<ul style="display: flex;"><li style="flex:1">F</li><li style="flex:1">E</li><li style="flex:1">M</li><li style="flex:1">A</li></ul>EDERAL MERGENCY ANAGEMENT GENCY TECHNICAL SERVICES DIVISION HAZARDS STUDY BRANCH RIVERINE EROSION HAZARD AREAS Mapping Feasibility Study September 1999 <ul style="display: flex;"><li style="flex:1">F</li><li style="flex:1">E</li><li style="flex:1">M</li><li style="flex:1">A</li></ul>EDERAL MERGENCY ANAGEMENT GENCY TECHNICAL SERVICES DIVISION HAZARDS STUDY BRANCH RIVERINE EROSION HAZARD AREAS Mapping Feasibility Study September 1999 Cover:House hanging 18 feetoverthe Clark Fork RiverinSanders County, Montana, afterthe rivereroded its bank inMay 1997. PhotographbyMichaelGallacher. Table of Contents Report Preparation........................................................................................xi Acknowledgments.........................................................................................xii Executive Summary......................................................................................xiv <ul style="display: flex;"><li style="flex:1">1. </li><li style="flex:1">Introduction........................................................................................1 </li></ul>1.1. Description of the Problem...........................................................................................................1 1.2. Legislative History.........................................................................................................................1 1.2.1. 1.2.2. 1.2.3. 1.2.4. National Flood Insurance Act (NFIA), 1968 .......................................................................3 Flood Disaster Act of 1973 ...............................................................................................4 Upton-Jones Amendment, 1988........................................................................................4 National Flood Insurance Reform Act (NFIRA), 1994........................................................7 1.3. Extent of the Problem...................................................................................................................7 1.4. Purpose and Scope of the Study...............................................................................................10 1.4.1. 1.4.2. Purpose..........................................................................................................................10 Scope.............................................................................................................................11 1.5. Mapping of Riverine Erosion Hazard Areas..............................................................................12 <ul style="display: flex;"><li style="flex:1">2. </li><li style="flex:1">Background of Riverine Erosion......................................................14 </li></ul>2.1. Fluvial Systems ...........................................................................................................................14 2.2. Factors Affecting Alluvial Channels...........................................................................................15 2.3. Channel Types ............................................................................................................................16 2.4. Channel Form and Processes....................................................................................................19 2.4.1. 2.4.2. 2.4.3. 2.4.4. 2.4.5. 2.4.6. 2.4.7. Definitions........................................................................................................................19 Geomorphic Characteristics............................................................................................20 Planforms........................................................................................................................22 Cross Section.................................................................................................................25 Slope ..............................................................................................................................26 Roughness and Bed Configuration..................................................................................27 Mechanics of Sediment Transport...................................................................................29 i2.5. Evaluation Methods for Channel Response to Imposed Changes.........................................30 2.5.1. 2.5.2. 2.5.3. Equilibrium Approaches...................................................................................................31 Fluvial Hydraulics.............................................................................................................32 Streambank Stability .......................................................................................................34 2.6. Computational Models................................................................................................................36 2.6.1. 2.6.2. 2.6.3. 2.6.4. 2.6.5. Modeling Approach.........................................................................................................37 Hydraulics .......................................................................................................................38 Sediment Transport ........................................................................................................39 Stability of Streambanks .................................................................................................39 Future Directions.............................................................................................................41 3. 4. Literature Review..............................................................................43 3.1. Research Sources and Search..................................................................................................43 3.2. Literature Summary....................................................................................................................43 3.3. Selected Documents...................................................................................................................43 Analysis of Case Studies..................................................................44 4.1. AMAFCASediment and Erosion Design Guide........................................................................46 4.1.1. 4.1.2. Overview.........................................................................................................................46 Detailed Description........................................................................................................46 4.1.2.1. Level 1 -- Geomorphic and Other Qualitative Analysis..........................................47 4.1.2.2. Level 2 – Quantitative Geomorphic and Basic Engineering Analysis .....................48 4.1.2.3. Level 3 – Quantitative Analysis Using Numerical Models.......................................51 4.1.2.4. Prudent Line Analysis ...........................................................................................51 4.1.3. 4.1.4. 4.1.5. 4.1.6. 4.1.7. 4.1.8. 4.1.9. Applicability .....................................................................................................................52 Limitations.......................................................................................................................53 Relevant References.......................................................................................................53 Mappability......................................................................................................................54 Cost................................................................................................................................54 Regulatory Potential........................................................................................................54 Summary........................................................................................................................55 4.2. Inventory and Analysis of Stream Meander Problems in Minnesota......................................56 4.2.1. 4.2.2. Overview.........................................................................................................................56 Detailed Description........................................................................................................56 4.2.2.1. Data Collection and Preparation...........................................................................57 4.2.2.2. Shift Measurement...............................................................................................57 4.2.2.3. Results Summary.................................................................................................58 4.2.2.4. Relationships Between Stream Parameters and Measured Results.....................58 <ul style="display: flex;"><li style="flex:1">4.2.3. </li><li style="flex:1">Applicability .....................................................................................................................58 </li></ul>ii 4.2.4. 4.2.5. 4.2.6. 4.2.7. 4.2.8. 4.2.9. Limitations.......................................................................................................................58 Relevant References.......................................................................................................58 Mappability......................................................................................................................59 Cost................................................................................................................................59 Regulatory Potential........................................................................................................59 Summary........................................................................................................................59 4.3. Probabilistic Spatial Assessment of River Channel Instability.................................................60 4.3.1. 4.3.2. Overview.........................................................................................................................60 Detailed Description........................................................................................................60 4.3.2.1. Methodology ........................................................................................................60 4.3.2.2. Case Study ..........................................................................................................62 4.3.3. 4.3.4. 4.3.5. 4.3.6. 4.3.7. 4.3.8. 4.3.9. Applicability .....................................................................................................................62 Limitations.......................................................................................................................62 Relevant References.......................................................................................................63 Mappability......................................................................................................................63 Cost................................................................................................................................63 Regulatory Potential........................................................................................................63 Summary........................................................................................................................63 4.4. Geomorphology and Hydrology of the Santa Cruz River, Southeastern Arizona.................64 4.4.1. 4.4.2. 4.4.3. 4.4.4. 4.4.5. 4.4.6. 4.4.7. 4.4.8. 4.4.9. Overview.........................................................................................................................64 Detailed Description........................................................................................................64 Applicability .....................................................................................................................66 Limitations.......................................................................................................................66 Relevant References.......................................................................................................66 Mappability......................................................................................................................67 Cost................................................................................................................................67 Regulatory Potential........................................................................................................67 Summary........................................................................................................................67 4.5. San Diego County Alluvial Studies.............................................................................................69 4.5.1. 4.5.2. Overview.........................................................................................................................69 Detailed Description........................................................................................................69 4.5.2.1. Computer Modeling..............................................................................................69 4.5.2.2. Definition of Hazard Areas....................................................................................70 4.5.3. 4.5.4. 4.5.5. 4.5.6. Applicability .....................................................................................................................70 Limitations.......................................................................................................................71 Relevant References.......................................................................................................71 Mappability......................................................................................................................71 iii 4.5.7. 4.5.8. 4.5.9. Cost................................................................................................................................72 Regulatory Potential........................................................................................................72 Summary........................................................................................................................72 4.6. City of Austin Technical Procedures for Watershed Erosion Assessments .........................73 4.6.1. 4.6.2. Overview.........................................................................................................................73 Detailed Description........................................................................................................73 4.6.2.1. Introductory Material.............................................................................................73 4.6.2.2. Impervious Cover Computation.............................................................................74 4.6.2.3. Watershed "Vital Statistics" ..................................................................................74 4.6.2.4. Urbanization Effects..............................................................................................75 4.6.2.5. Stream Inventory..................................................................................................75 4.6.2.6. Enlargement Potential...........................................................................................77 4.6.2.7. Nick Point and Meander Management..................................................................79 4.6.2.8. Prioritization of Erosion Problems .........................................................................79 4.6.2.9. Stream Management Recommendations.............................................................80 4.6.3. 4.6.4. 4.6.5. 4.6.6. 4.6.7. 4.6.8. 4.6.9. Applicability .....................................................................................................................80 Limitations.......................................................................................................................80 Relevant References.......................................................................................................80 Mappability......................................................................................................................81 Cost................................................................................................................................81 Regulatory Potential........................................................................................................81 Summary........................................................................................................................81 4.7. River Stability Studies for Virgin River, Santa Clara River, and Fort Pierce Wash, Utah ......83 4.7.1. 4.7.2. Overview.........................................................................................................................83 Detailed Description........................................................................................................83 4.7.2.1. Historical Evaluation, Virgin River ..........................................................................83 4.7.2.2. Geomorphic Evaluation, Virgin River.....................................................................84 4.7.2.3. Conclusion............................................................................................................86 4.7.2.4. Santa Clara River.................................................................................................87 4.7.2.5. Fort Pierce Wash.................................................................................................87 4.7.2.6. Recommended Management Plans.....................................................................88 4.7.3. 4.7.4. 4.7.5. 4.7.6. 4.7.7. 4.7.8. 4.7.9. Applicability .....................................................................................................................88 Limitations.......................................................................................................................89 Relevant References.......................................................................................................89 Mappability......................................................................................................................90 Cost................................................................................................................................90 Regulatory Potential........................................................................................................90 Summary........................................................................................................................90 4.8. Hydrologic and Geomorphic Studies of the Platte River Basin, Nebraska............................91 4.8.1. 4.8.2. Overview.........................................................................................................................91 Detailed Description........................................................................................................91 iv

RIVERINE EROSION HAZARD AREAS Mapping Feasibility Study

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