The world's population has more than doubled in the last 50 years (from 2.52 billion in 1950 to 6 billion in 2000). Furthermore, the United Nations (1999) estimates that 97% of growth occurs in the least developed countries, with Africa being the fastest growing area. Cities such as Bombay, Calcutta, Karachi, Jakarta, Nairobi, Manila, Lagos and Cairo are examples of rapid human concentration. This makes current planning strategies insufficient and ineffective (if they exist at all). Consequently, slums, squatters and informal settlements in those cities are the expression of the marginalization of a large and growing segment of city dwellers (Sietchiping 2000). It is undeniable that land use is constantly evolving. The rate of urbanization, deforestation, agricultural drainage, and plowing of natural grasslands have increased the potential for flooding (Ward 1978). Informal settlements are usually located in vulnerable and undeveloped areas such as deep valleys (Nairobi), river banks (Bombay), abandoned landfills (Manila) or dangerous slopes (Yaounde). They are known as disaster-prone areas (floods, landslides and health risks). It originated from difficult problems related to housing, immigration rates, politics, spatial planning, landlessness and employment in urban areas (Sietchiping 2000). Many build their homes and grow their food on river floodplains in cities (Douglas 2008). Flooding along some of the low-lying floodplains adjacent to major rivers can be widespread and long-lasting (Zillman 1999). In the case of the Ganges-Brahmaputra-Megna river system in Bangladesh, 110 million people are relatively defenseless in the floodplain of South Asia's most flood-prone river system (Smith 1996 p. 258). But risks are also great for settlements in small river basins subject to sudden flash flooding and along low-lying coasts where storm surges associated with cyclones can produce marine inundations several meters deep (Zillman 1999). Davis and Hall (1999) argue that poverty can push people to settle and work in precarious places, such as unstable riverbanks in agricultural areas. Of the large population of Asia, 89% of the working population of Thailand, 73% of that of Korea, 70% of that of Burma, 69% of that of the Philippines, and 67% of that of India are engaged in agricultural production (Bureau of Flood Control 1950). Alluvial river valleys and river deltas constitute the most suitable area for agriculture. The flat topography of these areas lends itself well to agriculture (Bureau of Flood Control 1950). In