ABSTRACT
Flooding is a very common environmental hazard with over 3,000 disasters recorded in the CRED database since 1900. This is because of the widespread distribution of river floodplains and lowlying coasts and their long-standing attractions for human settlement. Each year, floods claim around 20,000 lives and adversely affect at least 20 million people worldwide, mostly through homelessness. These figures are inexact because floods are linked to other environmental processes and can be difficult to classify. For example, floods can be the consequence of storms and tsunamis but they are also the cause of some epidemics and landslides. Although flood-related deaths and homelessness are concentrated in the LDCs, industrialised countries – which invest heavily in flood defence and emergency measures – suffer large economic losses. The degree of flood hazard is dependent on factors such as the depth and velocity of the water, the duration of the flood and the load (sediment, salts, sewage, chemicals) carried. Figure 11.1 shows some approximate hazard thresholds for depth and velocity. People and cars can be washed away in about 0.5 m of fast-flowing water. Buildings, and other obstructions, create turbulent scour effects and many buildings start to fail at velocities of 2 m sec1. The
physical stresses on structures are greatly increased when rapidly flowing water contains debris such as rock or ice. The collapse of sewerage systems and storage facilities for products like oil or chemicals means that flood waters create pollution hazards. In November 1994 over 100 people were killed in Durunqa, Egypt, when floods destroyed a petroleum storage facility and carried burning oil into the heart of the town.
