PORTADA:Maquetaci n 1 27/11/09 12:26 P gina 1 PUBLICATIONS OF THE GEOLOGICAL SURVEY OF SPAIN (IGME) Series: GEOLOGICAL HAZARDS/GEOTECHNICS No. 2 A Handbook on Flood Hazard Mapping Methodologies A Handbook on Flood Hazard Mapping Methodologies MAPAS DE PELIGROSIDAD (INGLES):Maquetacin 1 27/11/09 12:27 Pgina 1 A Handbook on Flood Hazard Mapping Methodologies Authors: A. Díez-Herrero L. Laín-Huerta M. Llorente-Isidro GEOLOGICAL SURVEY OF SPAIN Madrid 2009 MAPAS DE PELIGROSIDAD (INGLES):Maquetacin 1 27/11/09 12:27 Pgina 2 Series: GEOLOGICAL HAZARDS/GEOTECHNICS No. 2 Authors: A. Díez-Herrero L. Laín-Huerta M. Llorente-Isidro A Handbook on Flood Hazard Mapping Methodologies / Geological Survey of Spain. Area of Research in Geological Risks and Hazards; Díez-Herrero, A., Laín-Huerta, L., Llorente-Isidro, M. Madrid: Spanish Geological Survey, 2009 190 pgs; 86 figs; 29 cm (Geological Hazards/Geotechnics series) ISBN 978-84-7840-813-9 1. Flood hazard map 2. Floods. 3. Legend 4. Handbook. I. Geological Survey of Spain. II. Díez-Herrero, A. III. Laín-Huerta, L. IV. Llorente-Isidro, M. 556, 551.3, 911.2, 626, 627 This guide forms part of the products of the Geological Survey of Spain project entitled: “Investigación metodológica para la elaboración de cartografía de peligrosidad y riesgo ante avenidas e inundaciones (METAVENIDAS).” [Research on methodologies for flood hazard and risk mapping (METAVENIDAS)] directed by Luis Laín Huerta. No part of this book may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photography, record- ing or any information storage system without the prior written permission of the authors and publishers. Collaborators: Juan Antonio Ballesteros Cánovas, Virginia Ruiz Villanueva, María Jesús Mancebo Mancebo, Fernando Pérez Cer- dán, Ángel Martín-Serrano, Ángel Salazar Rincón, Francisco Nozal Martín and Miguel Mejías Moreno (IGME); An- tonio Cendrero Uceda (University of Cantabria); Jorge Olcina Cantos (University of Alicante); Antonio Jiménez Ál- varez and Concepción Marcuello Olona (CEDEX); Elena Fernández Iglesias (INDUROT, University of Oviedo); Mayte Rico Herrero (IPE-CSIC); José Francisco Martín Duque (UCM); Javier Lastra Fernández (Acunor); Montse- rrat Ferrer i Julià (Tecnosylva); Eduardo García Meléndez (University of León). Translation: Michael McCain Production and composition: Area of Research in Geological Risks and Hazards Department of Geoscientific Research and Prospective Geological Survey of Spain Layout: Soluciones Gráficas Chile S.L.L. Illustration: Cristóbal Aparicio Photomechanical reproduction and printing: Soluciones Gráficas Chile S.L.L. © GEOLOGICAL SURVEY OF SPAIN c/ Ríos Rosas, 23 – 28003 Madrid Tel.: +34 913495700. Fax: +34 914426216 Web: http://www.igme.es Laboratories: c/ La Calera, 1. 28760 Tres Cantos (Madrid) Tel.: +34 918032200. Fax: +34 918032200 I.S.B.N.: 978-84-7840-813-9 N.I.P.O.: 474-09-044-5 Depósito Legal: M-50313-2009 MAPAS DE PELIGROSIDAD (INGLES):Maquetacin 1 27/11/09 12:27 Pgina 3 INTRODUCTION Floods are the natural disasters with the greatest socio-economic impact after droughts, both globally and in Spain itself. Suffice it to recall the consequences of the floods which have in recent decades affected countries like Mozambique, the Philippines, China, Venezuela, the United States and Myanmar (Burma), to cite a few events which have received wide media coverage. In Europe, the great floods which took place in the centre of the continent in 2002 were an inflection point in the level of concern of European institutions with respect to this problem. In Spain, according to a study carried out by the Spanish Geological Survey (IGME) in collab- oration with the Consortium of Insurance Compensation1 in 2004, the direct economic losses resulting from floods during the period 1987-2002 reached nearly EUR 12 billion, that is to say, the equivalent of 0.1% of GDP. In addition, nearly EUR 26 billion in losses are predicted over the next 30 years. If we speak of the cost in terms of human life, there is a steady flow of victims each year (over 200 mortal victims in the past decade) due to events which have sparked profound social alarm. The floods in Biescas, with 86 mortal victims, Badajoz, with 21 victims, or Yebra (Guadalajara), with 10 victims, are proof of the latter point. Bearing this in mind, the action taken by public administrations must be steered towards adequate management of flood-related risks in an attempt to minimize them and mitigate their consequences. To achieve this, there are three traditional groups of measures: predictive, preventative and corrective. The predictive measures and techniques for floods are still in their incipient stages of development and include, among others, meteorolog- ical tracking of convective cells, or real-time hydrologic information systems. As regards the adoption of cor- rective measures, that is, post-catastrophe actions, or the financial assistance expressed through disaster zone declarations, it is clear that mere adoption per se unaccompanied any other type of measures logically results in social dissatisfaction. This is why most public administrations in developed countries have chosen, for decades, to focus their action on what we call preventative measures, which encompass those traditionally de- fined as ´non-structural´: spatial planning, assurance systems, civil protection and risk education. To be implemented, all of the measures, particularly non-structural preventative ones, require, as a preliminary and fundamental step in management, that a flood risk analysis be carried out, which involves a conducting de- tailed study of the risk elements (hazard, exposure and vulnerability). In this context, flood hazard mapping is a basic component in flood risk analysis studies as it permits the effective evaluation of the spatial distribution of the various elements of severity (such as water surface level, flow velocity, sediment transport, or character- istic times) and frequency (return periods or exceedance probability) of the flood phenomenon. Furthermore, they offer the utility of being able to link the maps and their associated databases to exposure and vulnerabil- ity maps in order to analyse and predict risk in an integrated manner using such tools as geographic informa- tion systems (GIS). In order for the production and publishing of these maps to fulfil the functions of accurate mapping and prac- tical utility, it is desirable to harmonise the methodologies used to make them, standardize the criteria and ar- rive at a consensus on which elements to represent and legends. To that end, a basic starting point in prevent- ing risk would be to draw up methodological guides which provide an inventory of the data-gathering and rep- resentation methods, map scales, zoning criteria and available computer programs. It is in this context that the publication of IGME’s “A handbook on flood hazard mapping methodologies” takes on its fullest meaning. José Pedro Calvo Sorando Director General of the Geological Survey of Spain 1 Consorcio de Compensación de Seguros. 3 MAPAS DE PELIGROSIDAD (INGLES):Maquetacin 1 27/11/09 12:27 Pgina 4 MAPAS DE PELIGROSIDAD (INGLES):Maquetacin 1 27/11/09 12:27 Pgina 5 FOREWORD In the past few decades, numerous plans, programmes, projects and systems for analyzing and mapping flood hazards have been implemented in Spain and in the rest of the developed countries. To cite a few examples in the international arena: the National Flood Insurance Program (NFIP) maps in the United States, the Flood Risk Prevention Plans in France2, or the recent European Community Directive 2007/60/EC on the assessment and management of flood risks, which lays down in its Chapter III the need to prepare flood hazard maps and flood risk maps for specific hydrographic areas by the year 2013. In Spain, the different public administrations at the government, Autonomous Region, county and local levels have implemented various initiatives, such as the National Flood Zone Mapping System3, promoted by the Di- rectorate-General of Water4 (Ministry of the Environment and Rural and Marine Affairs5), Autonomous Region master plan maps focused on spatial planning (PATRICOVA and Region of Murcia) and civil protection (Inun- cat, RICAM, Inunbal, Inungal), the compulsory natural risk maps in the environmental sustainability reports provided for in the Land Law (8/2007)6; in addition to other experiences in which potential flood-prone zones were mapped for different return periods (100 and 500 years), such as the LINDE and PICHRA programmes, the flood hazard studies by the River Basin Authorities for the protection of the public water domain7, etc. However, almost all of these initiatives lack clear and concise methodological handbooks making it possible to harmonise the resulting maps and thereby avoid inconsistencies and discrepancies in the administrative boundaries for which they were carried out. For this reason, what is lacking is an element of standardization, similar to the role played by the EXCIMAP exchange group in preparing the maps associated with the above- mentioned European Directive. Moreover, the Earth Sciences play an indispensable role in studying the origins and consequences of flash flood and flood inundation events. It is in this line of thought that the recent modification was made to the Royal De- cree on the Regulations on the Public Water Domain8 (RD 9/2008 of 11 January, Official Gazette9 No. 14 of 16 January 2008) which considers all of the methods valid with respect to delimitations since no priorities are es- tablished on this matter. In light of the above, this methodological handbook written by IGME on preparing flash flood and flood inun- dation hazard maps comes at an opportune moment as it provides methods and criteria pertinent to all of the abovementioned master plans and projects, as well as those to come in the short and middle term. Vicente Gabaldón López Director of the Department of Geoscientific Research and Prospective 2 Plan de prévention des risques d’inondation (PPRI).