FLOOD AFTER FIRE CALIFORNIA TOOLKIT A RESOURCE FOR TECHNICAL SPECIALISTS TO ASSESS FLOOD AND DEBRIS FLOW RISK AFTER A WILDFIRE September 2020 Version 1 Cover Photos courtesy of Ventura County: CENTER: Flooded road OUTSIDE, CLOCKWISE: Bird’s eye view of the Thomas Fire A culvert plugged by debris A car lifted by a debris flow Large rocks deposited in a road A gate holding back debris ii This Flood After Fire: California Toolkit is a collaborative, living document written by the California Silver Jackets Team. Silver Jackets is a partnership program that brings together Federal, State, local, and Tribal agencies to find collaborative solutions to complex flood risk management issues. Agencies that contributed to this guide include: Bureau of Land Management California Department of Forestry and Fire Protection California Department of Transportation California Department of Water Resources California Geological Survey California Office of Emergency Services County of Lake, California, Water Resources Federal Emergency Management Agency National Aeronautics and Space Administration National Ocean and Atmospheric Administration National Park Service National Weather Service Natural Resources Conservation Service Santa Barbara County, California U.S. Army Corps of Engineers, Engineer Research and Development Center U.S. Army Corps of Engineers, Sacramento District U.S. Forest Service U.S. Geological Survey Ventura County, California, Public Works Agency What is in This Toolkit? • A collection of tools, methods, and other resources – grouped into chronologically distinct periods of a flood after fire response timeline – to help assess the risks associated with flooding and debris flow after a fire. • Basic checklists and generalized procedures, written to encourage an interdisciplinary response to post-fire modeling and analysis. • Appendices to help guide those who do not frequently respond to fire events. For more experienced emergency response officials or those who become familiar with this toolkit, the matrices provided can act as a “quick reference” to commonly used models and data. • References and discussions on the roles different agencies of varying levels of government may have in response to wildfire. • Technical resources that are useful for well-trained and experienced technical specialists, not the general public or communities impacted by wildfires and the floods and debris flows that could follow them. The information provided is specific to California. Who is This Toolkit For? • GIS specialists, hydrologists, hydraulic engineers, or those with similar backgrounds. • Geohazard specialists, geologists, mitigation planners, soil scientists, or other natural resource professionals may find this toolkit informative, but of limited use. • Wildfire support staff such as Emergency Managers and those above who are responding to wildfires in the State of California. How is This Toolkit Used? • This toolkit is designed to be used on a computer, and uses links to accompanying documents, files, and websites/data sources that are built into the text. However, a hardcopy can be printed and referenced if the user has ample and adequate access to data. • For maximum benefit, this toolkit should be reviewed during the offseason (Chapter 2), or when there is not an emergency, so the reader becomes familiar with its structure and content. That said, this toolkit can be used during an emergency by relying heavily on the table of Contents and headings to take the reader to the most relevant sections. • Those who do not frequently assess flood risk after a wildfire should follow the chapters and sections in order, beginning with Chapter 3 (Fire Event and Pre-Flood). • Experienced emergency response officials or technical support staff can use the toolkit in the order they judge to be appropriate, based on what period of the fire response timeline they are in and what risk(s) they need to analyze and identify. • Experienced modelers familiar with how interagency teams in California cooperate and respond to wildfires may find that the appendices are a useful “quick reference”. In that case, much of the main text of the toolkit could be skipped, but used as a refresher. ii Table of Contents List of Tables ............................................................................................................................. 5 List of Figures ............................................................................................................................ 5 List of Acronyms and Abbreviations .............................................................................................. 6 1. Introduction ...................................................................................................................... 8 1.1. Fire Timeline and Response ..........................................................................................12 2. Pre-Fire (Offseason)...........................................................................................................14 2.1. GIS Preparedness ........................................................................................................14 2.1.1. Spatial Data and Products Library: Organization .......................................................15 2.1.2. Spatial Data: Collection and Updating .....................................................................17 2.1.3. The “Brick” – A Portable Data Library ......................................................................17 2.1.4. Pre-Event Assessment/Analysis and Cartographic Products ........................................18 2.1.5. Field Applications.................................................................................................19 2.2. H&H Impacts and Response..........................................................................................20 2.2.1. Software Updates, Maintenance, and Training .........................................................21 3. Fire Event/Pre-Flood (Time Tier 1) .......................................................................................22 3.1. BAER and WERT ..........................................................................................................24 3.2. GIS (Time Tier 1) .........................................................................................................35 3.2.1. Event Data: Collection and Organization ..................................................................37 3.2.2. Event Status: Initial Assessments & Analysis.............................................................38 3.2.3 Event Status: Cartographic Products .......................................................................40 3.3. H&H Event Checklist ....................................................................................................41 3.3.1. Watershed Model Setup .......................................................................................45 3.3.2. Initial Modeling: Pre-Event Conditions ....................................................................48 4. Post-Fire/Pre-Flood (Time Tier 2 & 3)...................................................................................49 4.1. GIS (Time Tier 2 & 3)....................................................................................................51 4.1.1. Event Data and H&H Model Preprocessing...............................................................51 4.1.2. Event Updates: Assessments and Analysis ...............................................................52 4.1.3. H&H Post-Modeling Processing and Cartographic Products ........................................53 4.2. H&H Products & Deliverables........................................................................................54 5. Post-Fire & Post-Flood .......................................................................................................56 5.1. GIS Reports ................................................................................................................57 5.2. Long-Term Responsibilities ...........................................................................................58 iii 5.3. Conclusion .................................................................................................................59 6. Appendices.......................................................................................................................60 6.1. Resource Timeline Matrix (LINK)....................................................................................60 6.2. Spatial Data Matrix (LINK) ............................................................................................60 6.3. H&H Model Matrix (LINK).............................................................................................61 6.4. GIS and H&H Output Products Matrix (LINK) ...................................................................61 7. References .......................................................................................................................62 7.1. Case Studies ...............................................................................................................68 iv List of Tables Table 1. General classification of flow behavior (modified from Lancaster et al., 2015)........................11 Table 2. Selected BAER and WERT post-fire flow estimation methods (see Kinoshita et al., 2013). ........29 Table 3. H&H data checklist. .......................................................................................................44