ELEVATION DATA FOR
FLOODPLAIN MAPPING

Committee on Floodplain Mapping Technologies

Board on Earth Sciences and Resources

Division on Earth and Life Studies

NATIONAL RESEARCH COUNCIL OF THE NATIONAL ACADEMIES

THE NATIONAL ACADEMIES PRESS

Washington, D.C.
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Elevation Data for Floodplain Mapping ELEVATION DATA FOR FLOODPLAIN MAPPING Committee on Floodplain Mapping Technologies Board on Earth Sciences and Resources Division on Earth and Life Studies NATIONAL RESEARCH COUNCIL OF THE NATIONAL ACADEMIES THE NATIONAL ACADEMIES PRESS Washington, D.C. www.nap.edu

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Elevation Data for Floodplain Mapping THE NATIONAL ACADEMIES PRESS 500 Fifth Street, N.W. Washington, DC 20001 NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. This study was supported through endowment funds provided by the National Academies. The opinions, findings, and conclusions or recommendations contained in this document are those of the authors and do not necessarily reflect the views of the organizations or agencies that provided support for the project. International Standard Book Number-13: 978-0-309-10409-8 International Standard Book Number-10: 0-309-10409-2 Library of Congress Control Number: 2007927598 Additional copies of this report are available from the National Academies Press, 500 Fifth Street, N.W., Lockbox 285, Washington, DC 20055; (800) 624-6242 or (202) 334-3313 (in the Washington metropolitan area); Internet http://www.nap.edu. Cover: Top image shows a FEMA flood insurance rate map overlaid on aerial orthoimagery from the U.S. Department of Agriculture’s National Agriculture Imagery Program. (Note that the images are not orthorectified.) Bottom image shows a digital elevation model called a triangular irregular network (TIN). TIN courtesy Dr. Pankaj Agarwal, Duke University. Cover design by Van Nguyen. Copyright 2007 by the National Academy of Sciences. All rights reserved. Printed in the United States of America.

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Elevation Data for Floodplain Mapping THE NATIONAL ACADEMIES Advisers to the Nation on Science, Engineering and Medicine The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Ralph J. Cicerone is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Charles M. Vest is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Harvey V. Fineberg is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy’s purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Ralph J. Cicerone and Dr. Charles M. Vest are chair and vice chair, respectively, of the National Research Council. www.national-academies.org

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Elevation Data for Floodplain Mapping COMMITTEE ON FLOODPLAIN MAPPING TECHNOLOGIES DAVID R. MAIDMENT, Chair, University of Texas, Austin SCOTT EDELMAN, Watershed Concepts, Greensboro, North Carolina ELVIN R. HEIBERG III, Heiberg Associates, Inc., Arlington, Virginia JOHN R. JENSEN, University of South Carolina, Columbia DAVID F. MAUNE, Dewberry and Davis, Fairfax, Virginia KAREN SCHUCKMAN, URS Corporation, Gaithersburg, Maryland RAMESH SHRESTHA, University of Florida, Gainesville National Research Council Staff ELIZABETH A. EIDE, Study Director JARED P. ENO, Senior Project Assistant

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Elevation Data for Floodplain Mapping MAPPING SCIENCE COMMITTEE KEITH C. CLARKE, Chair, University of California, Santa Barbara ROBERT P. DENARO, NAVTEQ Corporation, Chicago, Illinois SHOREH ELHAMI, Delaware County Auditor’s Office, Delaware, Ohio JIM GERINGER, ESRI, Wheatland, Wyoming GEORGE F. HEPNER, University of Utah, Salt Lake City JOHN R. JENSEN, University of South Carolina, Columbia NINA S.-N. LAM, Louisiana State University, Baton Rouge LEWIS A. LAPINE, South Carolina Geodetic Survey, Columbia MARY L. LARSGAARD, University of California, Santa Barbara XAVIER R. LOPEZ, Oracle Corporation, Nashua, New Hampshire ROBERT B. MCMASTER, University of Minnesota, Minneapolis SHASHI SHEKHAR, University of Minnesota, Minneapolis NANCY TOSTA, Ross & Associates Environmental Consulting, Ltd., Seattle, Washington EUGENE TROBIA, Arizona State Land Department, Phoenix Staff PAUL M. CUTLER, Senior Program Officer JARED P. ENO, Senior Program Assistant

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Elevation Data for Floodplain Mapping BOARD ON EARTH SCIENCES AND RESOURCES GEORGE M. HORNBERGER, Chair, University of Virginia, Charlottesville GREGORY B. BAECHER, University of Maryland, College Park STEVEN R. BOHLEN, Joint Oceanographic Institutions, Washington, D.C. KEITH C. CLARKE, University of California, Santa Barbara DAVID COWEN, University of South Carolina, Columbia WILLIAM E. DIETRICH, University of California, Berkeley ROGER M. DOWNS, The Pennsylvania State University, University Park JEFF DOZIER, University of California, Santa Barbara KATHERINE H. FREEMAN, The Pennsylvania State University, University Park RHEA L. GRAHAM, Pueblo of Sandia, Bernalillo, New Mexico RUSSELL J. HEMLEY, Carnegie Institution of Washington, Washington, D.C. MURRAY W. HITZMAN, Colorado School of Mines, Golden V. RAMA MURTHY, University of Minnesota (retired), Minneapolis CLAYTON R. NICHOLS, Idaho National Engineering and Environmental Laboratory (retired), Standpoint RAYMOND A. PRICE, Queen’s University, Kingston, Ontario, Canada BARBARA A. ROMANOWICZ, University of California, Berkeley JOAQUIN RUIZ, University of Arizona, Tucson MARK SCHAEFER, Global Environment and Technology Foundation, Arlington, Virginia WILLIAM W. SHILTS, Illinois State Geological Survey, Champaign RUSSELL E. STANDS-OVER-BULL, BP American Production Company, Pryor, Montana TERRY C. WALLACE, JR., Los Alamos National Laboratory, New Mexico THOMAS J. WILBANKS, Oak Ridge National Laboratory, Oak Ridge, Tennessee National Research Council Staff ANTHONY R. de SOUZA, Director PAUL M. CUTLER, Senior Program Officer ELIZABETH A. EIDE, Senior Program Officer DAVID A. FEARY, Senior Program Officer ANNE M. LINN, Senior Program Officer ANN G. FRAZIER, Program Officer SAMMANTHA L. MAGSINO, Program Officer RONALD F. ABLER, Senior Scholar VERNA J. BOWEN, Administrative and Financial Associate

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Elevation Data for Floodplain Mapping JENNIFER T. ESTEP, Financial Associate CAETLIN OFIESH, Research Associate JARED P. ENO, Senior Program Assistant NICHOLAS D. ROGERS, Senior Program Assistant TONYA FONG YEE, Program Assistant

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Elevation Data for Floodplain Mapping Preface The creation of floodplain maps is an important part of the National Flood Insurance Program. Floodplain maps define flood hazard zones and are used to determine whether flood insurance is required for buildings located near streams and rivers. The Federal Emergency Management Agency (FEMA) is undertaking an ambitious five-year program to update and make digital the floodplain maps of the nation. Some concerns have been raised in Congress about the adequacy of the framework map data available to support this task. The Committee on Floodplain Mapping Technologies, appointed by the National Research Council, was asked to identify and review the available mapping technologies that can provide base and elevation data for floodplain maps. The committee comprises individuals with expertise in surveying and remote sensing, geospatial data processing and mapping, hydrology and hydraulic engineering, flood risk assessment, and floodplain mapping, specifically in the technologies used for collection of digital elevation data. These technologies include light detection and ranging (lidar), interferometric synthetic aperture radar (IFSAR), and photogrammetry. More information about the committee is available in Appendix A of this report. In addition to information derived from its own expertise, the committee asked researchers and practitioners from federal and state agencies, academic institutions, and the private sector to communicate their expert knowledge of the principles, strengths, and weaknesses of various mapping technologies and the application of the resulting data to floodplain mapping. These individuals provided testimony on which data were required, collected, and/or accessible and why they were or were not used for floodplain mapping under various circumstances. An overview of the workshop during which much of this external testimony was discussed can be found in Appendix B. The committee also examined the relevant scientific literature and other published materials, relying particularly upon FEMA’s public documents related to its Flood Map Modernization program. This report and its recommendations are a result of the consensus of the committee.1 The recommendations specifically address the statement of task and indicate which technologies are most appropriate to meet the standards required by FEMA in generating floodplain maps for flood hazard assessments. Because digital elevation data collection affects other federal agencies, some of whom also partner with FEMA, the information contained in this report is written to be useful for Congress, as well as for federal, state, and 1 This report was initially released under the title “Base Map Inputs for Floodplain Mapping.” This title was modified, and similar editorial changes made in the report text, to be consistent with standard use of the term “base map” in the federal emergency management community.

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Elevation Data for Floodplain Mapping local agencies and practitioners involved in digital elevation data collection and floodplain mapping. The committee would like to express its appreciation to the many qualified and enthusiastic individuals who provided testimony, data, and advice during the course of the study; in particular, the committee would like to thank the Topographic Sciences Program of the United States Geological Survey Center for Earth Resources Observation and Science, located in Sioux Falls, South Dakota, for its guidance on the characteristics of the National Elevation Dataset. The committee is also indebted to the American Society for Photogrammetry and Remote Sensing which provided us with access to Digital Elevation Model Technologies and Applications: The DEM Users Manual (2nd edition, 2007), which it published. This manual, prepared by a large group of authors and edited by one of our committee members, contains a wealth of technical information about the creation and application of digital elevation data. All members of the committee provided key insights and took part in the drafting of the report in a very condensed time period. We were assisted in our efforts by National Research Council staff, in particular Elizabeth Eide and Jared Eno, who supported the committee’s activity in a very able way. The accuracy of floodplain delineation is a serious matter to citizens who live and work in flood-prone areas. One of the principal benefits of reports of the National Academies is to better inform citizens of some aspects of what their government is doing for them. Flood Map Modernization is a complex process the goals of which have evolved and the methods of which have become more refined as the program has advanced. This report describes that process and the role that mapping technologies play in it. We hope that our assessment of the adequacy of the nation’s base map and elevation data will be helpful to Congress and the nation in assessing the investment needed to develop better floodplain maps. David R. Maidment Chair January 2007

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Elevation Data for Floodplain Mapping Acknowledgments This report was greatly enhanced by input from participants at the public committee meeting held as part of this study: Glenn Bethel, John Dorman, Dean Gesch, Mike Godesky, Sue Greenlee, David Harding, Scott Hensley, Michael Hodgson, David Key, John LaBrecque, Jeff Lillycrop, David Loescher, Alan Lulloff, Chris McGlone, John Palatiello, Paul Rooney, Paul Rosen, George Southard, Jason Stoker, and Kirk Waters. Their presentations and discussions helped set the stage for the committee’s deliberations in the sessions that followed. The committee and staff are also indebted to Roger Cotrell, David Key, and Gray Minton of Watershed Concepts, Inc., for their help in preparing many of the figures contained in this report. This report has been reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the National Research Council’s Report Review Committee. The purpose of this independent review is to provide candid and critical comments that will assist the institution in making its published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. We wish to thank the following individuals for their participation in the review of this report: Robert Dalrymple, Johns Hopkins University, Baltimore, Maryland Lloyd Duscha, Independent Consultant, Reston, Virginia David Ford, David Ford Consulting Engineers, Inc., Sacramento, California George Lee, U.S. Geological Survey, Menlo Park, California Riadh Munjy, California State University, Fresno James Plasker, American Society for Photogrammetry and Remote Sensing, Bethesda, Maryland Robert Gilmore Pontius, Jr., Clark University, Worcester, Massachusetts Jery R. Stedinger, Cornell University, Ithaca, New York Gary Thompson, North Carolina Geodetic Survey, Raleigh Although the reviewers listed above have provided many constructive comments and suggestions, they were not asked to endorse the conclusions or recommendations nor did they see the final draft of the report before its release. The review of this report was overseen by Barbara Buttenfield, University of Colorado, Boulder, and Frank H. Stillinger, Princeton University, New Jersey. Appointed by the National Research Council, they were responsible for making certain that an independent examination of this report was carried

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Elevation Data for Floodplain Mapping out in accordance with institutional procedures and that all review comments were carefully considered. Responsibility for the final content of this report rests entirely with the authoring committee and the institution.

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Elevation Data for Floodplain Mapping Contents     SUMMARY   1 1   INTRODUCTION   10      1.1  Creating Floodplain Maps,   12      1.2  Origin of This Study,   12      1.3  Statement of Task and Report Structure,   13      1.4  Limitations of This Study,   14 2   FLOOD MAPPING   16      2.1  Flood Modeling,   17      2.2  Flood Damage,   20      2.3  Flood Mapping,   21 3   FEMA’S MAP MODERNIZATION PROGRAM   24      3.1  The FEMA Flood Insurance Rate Map,   24      3.2  FEMA Engineering Study Types,   28      3.3  Flood Insurance,   33      3.4  FEMA’s Map Inventory,   37      3.5  FEMA’s Processes and Procedures—1972 to 2002,   38      3.6  FEMA’s Processes and Procedures—2002 to 2006 Flood Map Modernization,   39      3.7  Creation of FEMA’s Five-Year Plan—MHIP,   40      3.8  FEMA’s Method for Risk Determination and Mapping Prioritization,   41      3.9  FEMA Map Quality Standards,   44      3.10  FEMA’s Current Use of Elevation Data,   45      3.11  Bathymetry,   49      3.12  Models for Elevation Data,   50      3.13  DEM Versus TIN Mapping,   52      3.14  Hydro-enforced Streamlines,   54      3.15  Chapter Summary,   54 4   REMOTE SENSING TECHNOLOGIES FOR FLOODPLAIN MAPPING   57      4.1  Concepts and Terms,   57      4.2  Photogrammetry,   63

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Elevation Data for Floodplain Mapping      4.3  Light Detection and Ranging,   72      4.4  Interferometric Synthetic Aperture Radar,   78      4.5  Chapter Summary,   87 5   ASSESSMENT OF FLOODPLAIN MAPPING TECHNOLOGIES   89      5.1  Observations on FEMA’s Map Modernization Program,   89      5.2  Collection of Orthoimagery Base Maps,   91      5.3  Collection of Digital Elevation Data,   99      5.4  Chapter Summary,   112 6   CONCLUSIONS AND RECOMMENDATIONS   115      6.1  Adequacy of Base Map and Elevation Information,   115      6.2  Available Mapping Technologies,   117      6.3  Elevation for the Nation,   119     REFERENCES   121     APPENDIXES          A  Biographical Sketches of Committee Members and Staff   127      B  Workshop Agenda and Participants   132      C  Glossary   135      D  Acronyms   149