Impact of Floods on Heritage Structures

Abstract

Miloš Drdácký Photo by Miroslav Kučera, with permission Throughout human history, floods have played a very important role, mainly due to their adverse impacts on cultural heritage. Floods lead to the loss of historical monuments, devastation of historic sites, changes in the cultural landscape, and also to the disappearance or substantial distortion of intangible heritage. Due to periodic changes in climatic conditions over recent years, we have witnessed increasingly frequent major floods and related events that pose a substantial threat to cultural heritage worldwide. These include the floods in Central Europe in 2002, the New Orleans flood in 2005, numerous floods in South Asia in 2007 and 2009, as well as severe floods in Central Europe again in 2010. Engineering experience acquired during the course of major floods has provided comprehensive knowledge and reliable data about the impact of flooding on historic objects and sites. This experience can serve as a basis for establishing guidelines and recommendations for the effective protection of cultural heritage in emergency situations. River floods are the most common type of natural disaster in many European and Asian regions. Recent European studies have pointed to a significant increase in the frequency and severity of river floods due to the apparent development of global warming. However, floods, being highly impactful phenomena, are well documented with details including social and economic impacts. Data on the height of water during the flood culmination are usually well documented in situ, in various types of high water line records. Such data show that flooding is a natural occurrence, and has been a frequent loading factor for historic buildings along rivers and historic bridges. For example, a detailed evaluation of the water gauge of the Lahn River in Germany shows that the bridges suffered 60 floods between 1255 and 1984, averaging a flood every 12 years. Of these, 22 were major floods. A review of the impact of floods on cultural heritage objects has therefore been chosen as a useful subject for this special issue. Another reason for choosing this topic is the shortage of systematic information on the damage and failure mechanisms of flooded historic structures and materials. Various reports evaluate the threat to densely urbanized river or coastal regions posed by a rise in sea level. These works typically focus on the impact of floods on human life, housing, and productive infrastructure. However, there is no doubt that the damage will increase significantly due to the loss of cultural and natural heritage assets. The rising sea level and increasing human exploitation of land along rivers have increased the occurrence of floods in areas that have seldom or never experienced them. Quite dangerous for cultural heritage, namely archives and museums, are so-called flash floods, characterized by a rapid rise and fall of floodwaters with peak flows occurring within hours of heavy rain. The occurrence of this hazard, almost forgotten in recent centuries due to rather favorable climatic situations, now seems to be on the rise. Taking into account this probable increase in threats to cultural heritage sites in Europe, the European Commission EC has decided to support a joint research project on Cultural Heritage Protection against Flooding, under the acronym CHEF. The project gathered data on the impact of floods on both moveable and immoveable cultural heritage objects and sites, establishing a sound source of information for further dissemination. This contributed to the decision of the Journal's editor Ken Carper to prepare a special issue. Though the main goal of the EC CHEF project was to provide suggestions for preparedness and prevention of damage and loss of cultural heritage, a substantial part of the project was devoted to an analysis of flood impacts. This special issue presents some of the results of the analysis and categorization of damage to materials and structures. The aim is to categorize adaptation strategies and design guidelines for preventive and remedial measures. The outputs include scientific references to specific flood phenomena for professionals, and clearer guidelines and recommendations for nonprofessional readers, mostly owners or managers of architectural or cultural heritage sites. The sequence of papers follows a scheme, starting with a rather general paper on a methodology to predict the probability of the occurrence of floods, followed by descriptive papers on the effects of floods on materials and structures. Finally, there is a review of some tools for damage assessment, illustrated by a case study of a historic bridge. The introductory paper Holický and Sýkora proposes a general framework for flood risk assessment, with special reference to cultural heritage issues of risk optimization and decision-making about protective measures. It suggests a theoretical model suitable for predicting the flows and the extent of future floods