Floods of the Tiber in Ancient Rome

Introduction

Introduction Floods and History 1 ∫ loods and civilization have always been companions.1 The earliest civilizations, such as those in Mesopotamia, arose along rivers in floodplains. The reasons for settling in such hazardous regions were obvious; rivers offer routes of communication , and the floods themselves can deposit and renew the soil, increasing agricultural yields. The very factors that make these areas attractive for settlement are the same ones that make them vulnerable to devastation caused by floods. The flat floodplains between the Tigris and Euphrates provided fertile ground for the type of intensive agricultural cultivation that would produce the surpluses necessary to support cities and empires, but these lands were also subject to sudden and destructive floods. The most dramatic example of the beneficial effects of floods is, of course, the civilization of ancient Egypt, whose entire economy was based upon the regular annual flooding of the Nile. Throughout history human populations all around the world have tended to cluster most densely along riparian corridors, many of which are prone to violent flooding. Although farmlands situated in such areas may suffer the loss of a crop during a flood yet retain much of the property’s intrinsic value once the waters have receded, heavily urbanized areas are a different matter. Not only is population density much higher in urban as opposed to rural set- tings (with concomitant potential for greater loss of life), but the physical structures of cities themselves represent enormous investments of capital that are vulnerable to a flood’s destructive power. Devastating floods are not just a problem of the ancient world, however. As people continue to settle in floodplains, and as cities grow ever larger and more densely populated, the damage caused by floods continues to rise.2 In the United States, for example, where there have been decades’ worth of massive civil engineering projects aimed at controlling or diverting floods, the annual economic losses from floods are still increasing at a rate of 4% per year in real terms. From 1925 to 1994, the annual damages from floods in the United States, even when converted into 1990 dollars, have steadily increased from an average of around $100 million to more than $3 billion per year.3 The desire to live in prime real estate and the increasing size and technological complexity of cities have simply provided a richer landscape of expensive targets for natural disasters. In addition, all the technological innovations of the past several centuries and the gigantic and costly efforts at flood control have proved futile against the force of major floods, as evidenced by the catastrophic Mississippi floods of 1993, which inundated 20 million acres in nine states, destroyed 50,000 homes, and flooded 75 towns. The damage from this one meteorological event was approximately $20 billion, resulting from a combination of destruction and harm to property and infrastructure, disruption of transportation, and agricultural losses.4 In the latter part of the 20th century, more than 80% of the presidentially declared natural disasters in the United States were caused by floods.5 A study by the U.S. Office of Foreign Disaster Assistance concluded that since 1964, floods outside the United States have killed more than 130,000 people , rendered 70 million homeless, and negatively affected more than 1 billion.6 Moving water has huge power. Floodwaters easily have the force to sweep away bridges, topple buildings, and lift boulders weighing several tons. Some idea of the potential power in water can be gauged by the yardstick formula that 1 inch of rainfall dropping from 1,000 feet over 1 square mile has a potential energy equivalent to 60,000 tons of TNT (three times the power of the Hiroshima nuclear bomb).7 Not least of a flood’s harmful effects are the difficulties involved in cleanFloods of the Tiber in Ancient Rome 2 ing up after the waters recede. Added to the physical task of clearing away the debris carried about by the waters are health hazards caused by backed-up sewers spreading dangerous bacteria as well as by the disposal of the corpses of animals and humans killed by the flood. Floods often leave behind vast quantities of silt and mud. The wellknown Florence flood of 1966, for example, left the city coated in an estimated 600,000 tons of viscous, stinking mud.8 In areas without effective warning systems, the potential for loss of life from floods...