Investigation of effective factors on flooding of Mahneshan-Angoran basin, Iran

Understanding flood phenomena and estimating flood potential play an important role in flood management and forecasting in any region. Due to the flooding of Mahneshan-Angoran basin, located in Zanjan province, Central Iran, in this study, the effective factors on flooding of this basin were investigated. For this purpose, first the basin curve number map was created by combining soil maps, land use, Digital Elevation Model and Look up table involving GIS environment. Then, using AHP Hierarchical Analysis method and based on the combined effects approach, appropriate weights were assigned to each of the slope factors, slope direction, land use, curve number, branch ratio, drainage density, precipitation, basin length and basin lithology. A flood risk map was prepared from the overlap of the weighted layers in the GIS environment. The results of AHP method showed that the highest weight among the effective factors is equal to 0.326, which belongs to the factor of the basin Curve Number. Other effective factors are: land use, slope, rainfall, drainage density, branching ratio, basin length, slope direction and lithological factor, which respectively have weights affecting flooding equal to 0.174, 0.142, 0.118, 0.090, 0.051, 0.042, 0.042 and 0.016. According to the obtained flood plan, it was observed that the western parts of the basin have a higher risk than other parts of the basin due to higher altitude and more rainfall, which is itself a proof of the accuracy of the calculations.