The rate of movement of people from rural areas to large settlements (cities) in recent time has increased, and most large settlements have developed near large rivers or on the coast. The proximity to rivers of large settlements is no accident as the river provides water and also a navigational channel for trade. Harbours along the coast have also become large settlements as ships dock for trade. Unfortunately, natural disasters tend to affect coastal and river areas more severely. Hurricanes, tropical storms and tsunamis are all natural disasters that disproportionately affect coastal areas. Flooding of rivers often inundates settlements on the river flood plain.