Flood zonation of Agerloo Cay Basin using the L-THIA method and fuzzy logic

A flood is a very simple natural phenomenon that occurs when a body of water rises to overflow land that is not normally submerged (Ward, 1978). At the same time, a flood is a very complex phenomenon that connects the natural environment, people, and the social systems of their organization. Flood is the most expensive and devastating natural hazard (Wilby and Keenan 2012; Sanyal and Lu 2004), and it continues to be a concern in many parts of the world (Jha et al. 2012; Kundzewich et al. 2010; Chang and Franczyk 2008). Scenarios of future climate indicate a likelihood of increased intense precipitation and flood hazard in many areas (cf. Kundzewicz et al., 2010). Floods are currently one of the greatest threats to social security and sustainable development, and it is estimated that floods affect around 20–300 million people every year (Hirabayashi and Kanae 2009). In recent decades many studies have been carried out on floods that mainly approached to flood risk management. Flood inundation models are defined as the tools which could simulate the rivers hydraulic and also occurred floods in flood plains (Horrit, 2007, 61). Modern flood management should attempt to analyses the full scope of a flood event, using integrative concepts and taking into account multifaceted expertise from diverse fields. Reliable flood risk assessment and the development of effective flood protection measures require thorough knowledge about flood frequencies at different points in a catchment. In this research, quantitative approaches in order to flood zonation were used for the Ajirloo Chay Basin. Topographic maps with scale of 1: 50,000, digital elevation model (DEM) with 27 m resolution, and satellite imagery (Landsat 3 and 4 :2013) are most important materials in this research. In this study for flood hazard zonation were used the L-THIA method and fuzzy logic quantitative approaches. Fuzzy theory is inaccurate and ambiguous concepts and a variable makes the math. In this study, the operator sum, algebraic product and gamma are used. In order to run the model and research used from a series of climatology data, geomorphology and land surface coating. In flooding zonation an area can be considered many physiographic parameters that can influence. Among these parameters we select nine factors as the most important factors that influence in flooding. These nine factors are: drainage density, hydrologic soil groups, slope, climate, land use, run off, land units, altitude, and lithology.It is important for preventing and decreasing the effect of flood to avoiding expounding these risks. Zonation flooding that can be adopted. In this study we used LHTIA models and fuzzy logic in Ajirloo Chay basin. For this research we got help nine factors includes (altitude – climate – land units – slope – lithology – drainage density –hydrologic soil groups – run off and land use). In this area the results show that more than flood zonation are in very low, low and mediums risk classes (about 65/6 %) that these area are located in western and bathetic water shed and the most high risk area located in the eastern half and the northeast. The high class of land drainage density are in this area of land that is the factor of being prone to flooding The concentration of run off in the Ajirloo chay basin is in the eastern portion and in the upstream of the basin. Natural factors such as high slopes and high altitudes and poor vegetation can aggravated the flooding of the eastern portion of the basin and increase the flood hazard in this portion of the basin. Percent of high risks land is in much and too much potential that included (34/4%) of total area which is remarkable. According to the final map obtained from flooding zonation and for the sustainable development should be prevented from constructions in area with very high and high risk.The concentration of run off in the Ajirloo chay basin is in the eastern portion and in the upstream of the basin. Natural factors such as high slopes and high altitudes and poor vegetation can aggravated the flooding of the eastern portion of the basin and increase the flood hazard in this portion of the basin. Percent of high risks land is in much and too much potential that included (34/4%) of total area which is remarkable. According to the final map obtained from flooding zonation and for the sustainable development should be prevented from constructions in area with very high and high risk.The concentration of run off in the Ajirloo chay basin is in the eastern portion and in the upstream of the basin. Natural factors such as high slopes and high altitudes and poor vegetation can aggravated the flooding of the eastern portion of the basin and increase the flood hazard in this portion of the basin. Percent of high risks land is in much and too much potential that included (34/4%) of total area which is remarkable. According to the final map obtained from flooding zonation and for the sustainable development should be prevented from constructions in area with very high and high risk.