A Tsunami in Lisbon Where to run? Daniel André Silva Conde Dissertação para obtenção do Grau de Mestre em Engenharia Civil Júri Presidente: Prof. Doutor António Jorge Silva Guerreiro Monteiro Orientador: Prof. Doutor Rui Miguel Lage Ferreira Co-Orientador: Prof. Doutor Carlos Alberto Ferreira de Sousa Oliveira Vogal: Prof. Doutora Maria Ana Viana Baptista Vogal: Engenheira Maria João Martins Telhado Outubro 2012 To my parents, Armando e Guilhermina. Thank you. Aos meus pais, Armando e Guilhermina. Obrigado. Acknowledgments This dissertation was developed at Instituto Superior Técnico - Technical University of Lisbon, Portugal, under the guidance of Professors Rui M. L. Ferrira and C. Sousa Oliveira. During this time, part of the work was supported by CEHIDRO - Centro de Estudos de Hidrossistemas - with two research initiation scholarships, also under the guidance of Professor Rui M. L. Ferreira. For the great opportunities that were given to me with no hesitation and for all the support, knowledge and motivation transmitted throughout this year, my sincere gratefulness to Professor Rui M. L. Ferreira. And I really do mean sincere. My many thanks to Ricardo for all the support and valuable help with STAV-2D. And of course to Edgar, for keeping the morale high when odds weren’t. Also, to Professora Maria Ana Baptista, my sincere thanks for all the kindness and availability. Without her contribution this work wouldn’t be possible. To Professor C. Sousa Oliveira for the thoughtful insights about various topics on seismicity and tsunamis. To my dear colleagues, specially André Marques and Pedro Pinotes, for making those hardworking hours as enjoyable as they could have been. Also to my fellow colleagues and friends at the Residência Engo Duarte Pacheco for providing the most hilarious 5 years that one could have had. My non-translatable-to-words gratitude to my parents. To my mother, Mira, and my father, Armando, for the constant support, guidance and love throughout my entire existence. To my grandfather, Joaquim, for the sensitive human being that he is and inspires to be. To my grandmother, Celeste, for being the craziest grandmother on this earth. And I mean this as the truest compliment. To my grandmother, Alcínia, for all the support and welcoming affections every single time she laid eyes on me. To my godparents, Fátima and Sérgio, for all the support, affection and enjoyable moments that we have had together so far. Also, my affectionate gratitude to my older "godfather", Sérgio, whose memory will last forever. A very special place for the younger family members. To Zi and Lino for having the most inspiring relation that can be seen between two brothers. Everyone feels better if you’re around. Also, to the rising star in the game (football!), Miguel for the sincere feelings and affections. To Catarina for the special i connection we share. No matter how long or how far I am away from all of you, I will never cease to have four brothers. And that’s about it. Oh wait... (ahah!) my loving gratitude to my girlfriend, Dora, for making the last 5 years probably the best ones that I have had so far. Thank you for fulfilling a long lasting void. It would take forever to thank everyone I owe some part of myself or my life. To all those I have not mentioned, my apologies and sincere thanks. ii Resumo Uma revisão recente do histórico de tsunamis em Portugal mostrou que o estuário do Tejo foi afetado por vários tsunamis catastróficos ao longo dos últimos dois milénios. Dada esta herança histórica, e a crescente consciencialização devida a fenómenos recentes com mediatização mundial, o presente trabalho procura fornecer informação relevante quanto à exposição das zonas ribeirinhas do estuário do Tejo a um tsunami semelhante ao ocorrido em 1 de Novembro de 1755. Novas abordagens, teóricas e metodológicas, foram usadas para modelar um cenário de Tsunami, com especial enfase para a propagação em terra. Um dos aspetos mais relevantes desta fase de um tsunami é a sua capacidade de incorporar detritos, sejam eles de origem natural, como sedimentos ou vegetação, ou artificial, como ruínas de infraestrutura construída ou outros equipamentos do quotidiano humano. Um modelo conceptual específico para escoamentos deste tipo - debris flows - foi revisto e ampliado com um flexível esquema de condições de fronteira. O modelo numérico contempla as mais recentes técnicas de discretização matemática e uma implementação computacional eficiente. Os seus fundamentos teóricos são apresentados a um nível introdutório enquanto que as novas funcionalidades são exaustivamente explicadas, demonstradas e discutidas. Um esforço muito considerável foi direcionado para a discretização da cidade de Lisboa. O ambiente con- struído deixa de ser um simples pano de fundo para visualizar resultados e passa a definir, explicitamente, a superfície do terreno. Todas as estruturas relevantes foram adequadamente modeladas com modelos digitais de terreno e malhas computacionais muitíssimo finas para a escala do problema em mão. Os resultados são apresentados em vários níveis diferentes, desde perspetivas abrangentes a análises detalhadas ao nível de cada arruamento. Nestas últimas, é fornecida informação pormenorizada quanto aos tempos de chegada do tsunami, as suas propriedades hidrodinâmicas e os padrões de deposição de detritos subsequentes à inundação. Este estudo demonstrou que vários locais na frente ribeirinha do estuário do Tejo são especialmente preocupantes no que a um cenário de Tsunami diz respeito. Este documento fornece informação relevante para apoiar o planeamento das respostas de socorro e eventual evacuação da cidade, constituindo mais um passo na promoção da segurança dos cidadãos de Lisboa. Palavras-Chave: Tsunamis, modelação matemática, estuário do Tejo, Lisboa iii iv Abstract A recent revision of the catalogue of tsunamis in Portugal has shown that the Tagus estuary has been affected by catastrophic tsunamis numerous times over the past two millennia. Provided this historical heritage, and the growing awareness due to recent events worldwide, the present work aims at providing relevant data on the exposure of the Tagus estuary waterfront to a tsunami similar to the one occurred on the 1st November of 1755. New theoretical and methodological approaches to tsunami modeling were employed, with special empha- sis given to propagation over dry land. One of the most relevant features of this stage of the tsunami is its ability to incorporate debris, either natural sediment incorporated from the bottom boundary or remains of human built environment. The increased mass and momentum of the run-up can inflict tremendous damage and, regrettably, severe human losses. A conceptual model specifically suited for describing debris flows is reviewed and extended with flexible boundary conditions. The employed numerical tool features the most up to date mathematical dis- cretization techniques and an efficient computational performance. The theoretical fundamentals of the numerical model are presented at an introductory level while the new features implemented are given a thorough explanation and discussion. A very considerable effort was directed to Lisbon’s topology discretization. The built environment is no longer seen as a simple background layer for result visualization, it actually explicitly defines the terrain surface. All relevant structures are adequately modeled with very fine elevation models and computational meshes, provided the scale of the problem at hand. The results are provided at different levels, ranging from generic overviews to street-level analysis on designated areas. At these locations detailed data on wave arrival times, hydrodynamic features of the advancing inundation front and urban debris scattering patterns are provided. This study has shown that several locations on the Tagus estuary waterfront are especially worrisome in what respects to a tsunami impact scenario. The present document provides relevant information to support the design of emergency response plans, comprising one further step in promoting the safety of Lisbon’s citizens. Keywords: Tsunamis, mathematical modelling, Tagus estuary, Lisbon. v vi Notation A Cell area [L2] C Sediment concentration [−] CL Homogenous, depth-averaged sediment concentration in layer L [−] Cf Friction coefficient [−] c Shallow water wave velocity [ms−1] −1 c~ik Approximate c in k edge [ms ] ds Reference sediment diameter [m] (n) −1 e~ik n eigenvector [ms ] E Flux vector fsij Stress tensor [P a] F~ Generic force [N] F Flux vector in x G Flux vector in y g Gravitic acceleration [ms−2] H Source terms vector h Fluid height [m] H Average depth [m] hL Thickness of layer L [m] hL Fluid height on the left side of a shock [m] hR Fluid height on the right side of a shock [m] ~n Unit normal to a plane [m] 1=3 −1 Ks Manning-Strickler coefficient [m s ] L Wavelength (KdV notation) [−] Ll Lower interface of a given layer [−] Lu Upper interface of a given layer [−] p Bed porosity [−] p Hydrostatic Pressure [P a] PL Depth-averaged hydrostatic pressure in Layer L [P a] 3 −1 qs Solid discharge [m s ] ∗ 3 −1 qs Solid discharge capacity [m s ] R Friction source term vector s Specific sediment gravity [−] S Shock speed [ms−1] tik Unit tangent to k edge, in natural rotation from nik [m] T Bottom slope source terms numerical flux matrix Tij Depth integrated turbulent tensions tensor [P a] −1 uφ Velocity associated with the vertical mass flux [ms ] −1 uI Interface velocity [ms ] uL Velocity on the left side of a shock [m] uR Velocity on the right