The natural disasters that form part of the nature of our environment usually occur so severely that they usually cause many casualties and losses. The ordinary conditions of everyday life of human beings and the social structures and infrastructure of the region suddenly become disrupted and people suffer and are left in distress. As a result, the affected community is at once in serious need of food, clothing, shelter, medical and health care, and protection against adverse environmental factors (Abedi, Ghodratollah, 1998; p. 53). The natural disasters of Iran fall into three categories:
A - Climatic disasters like flood - drought - storm - avalanches – extremely cold weather – snowstorm - frost - thunderstorms - severe heat and cold - forest fires (Gilan, Mazandaran, Golestan) - sand storm.
B. Dangers from some geological and tectonic processes (earthquake, landslide, debris flow, mud flow).
C - Environmental hazards including extension of salt pans, desertification, environmental degradation.
According to the scientists’ climatic division, our country is part of the arid and semi-arid climate of the world. One of the characteristics of this type of climate is the imbalanced distribution of precipitation in time and space, so that in one year it suffers from low degree of precipitation, or, in other words, from drought, and in another year it is struck by abnormal and untimely increase of precipitation, and as a result the overflow of seasonal and permanent rivers and consequently formation of flooding, causing extensive damage to agricultural land and urban and rural facilities. In coastal areas of the Caspian Sea, the risk of sea water penetration and the operation of waves are among other natural disasters causing damage to the north of the country (National Committee for Natural Disaster Mitigation; 1998; p. 4). The flood in Gilan province is a major threat from both life loss and economic point of view, and all economic and communication infrastructures including dams, irrigation canals, roads, bridges and other investments in agricultural and non-agricultural sections have been exposed to threat and destruction. In this regard, the objectives of this paper are to identify the causes of flood and its undeniable effects in the region.