Evaluation of Fuzzy Logic Relative to other Conceptual Models in Zoning of Flooding with Emphasis on Geomorphological Aspects

The nature has always shown its destructive face with the phenomena such as floods، volcanoes، earthquakes and…These risks have been always considered as a threat to human activities. Davarzan basin as a case study has been studied from this approach. This basin is located in west of Sabzevar Plain. The area of this basin is equal to 498. 69 kilometers. The issue under study is that every year a large portion of the river water is wasted and damages to agricultural activities. The research aim is to determine the flooding zones by zoning maps. Lack of hydrometric station، hydrological data and statistics and impassable of the areas at upstream of the basin for field works and the necessity for long term measurements have been the main problems of this research. In this study، GIS software and conceptual models have been used as the main tools. In determining the flooding zones، several factors are involved and each with different degrees of importance impact on zoning، thus، the natural condition like slope، lithology، morphometry، soil type، CN and vegetation condition are the main data of research. However، fuzzy algebraic sum operator as recognized 91. 03% of the basin with very high flooding and 0. 13 percent with flooding and therefore davarzan basin has low flooding sensitivity. Thus the fuzzy gamma operator among all operators in the models studied in GIS، has the high accuracy in flood zoning of basins in davarzan basin. This model also has determined 18. 82 percent of the basin located in high zone of flooding and 24. 62 percent of basin is placed in very high flooding. Units that are consistent with low flooding shall have the lowest weight. So that 19. 32 percent has been identified as low flood and 37. 24 percent as moderate flood. Finallt، the final result has been presented in the form of zoning maps.