can be divided into primary hazards that occur due to contact with water secondary efffects that occur because of the flooding such as disdisruption of services, health impacts such as famine and disease and tertiary effects such as changes in the position of river channels. Throughout the last century flooding has been one of the most costly disasters in terms of both property damage and human casualties. Major floods in chaina,for example,killed about 2 million people in 1887 , nearly 4 million in 1931 , and about 1 million in 1938 The 1993 flood on the upper Mississippi river and Midwest killed only 47 people, but the U.S. Army Corps of Engineers estimates the totle economic loss at between 15 and 20 billion dollars(see U.S. Army Corps' web site)