Flood risk assessment using a combination of cellular automated and SCS models In the northern slopes of Central Alborz (Case study: Lavijrood watershed)

Population growth, accumulation of capital and the expansion of urbanization in places prone to danger, lead to the emergence of urban society with high vulnerability to accidents. The increasing development of societies and the complexity of their internal and external relations, the importance of management and planning in reducing disasters and their effects on human settlements is becoming increasingly apparent.The northern slopes of the Central Alborz, especially the Lavijrood watershed, mainly due to topographic and physiographic conditions, climatic conditions, non-compliance with technical specifications in the construction of roads and technical buildings and encroachment on the river, geology and other factors affecting runoff, have The potential for flood production is at certain times of the year. In this research, we investigated the performance of the cellular automata (CA) and SCS model as a suitable estimation method, and examined the possibility of integrating the method with the ArcGIS application to simulate the flood hazards and the hydrograph flow for the Lavijrood. The runoff height and the flood hazard were obtained through the SCS method. The flood simulation using the SCS method requires the data of land use, hydrologic groups of soils, Digital Elevation Map (DEM), rainfall, and the roughness coefficient of the basin. The raster format of all these layers was prepared with cell sizes of 30×30 m. A large part of the Lavijrood watershed belongs to the hydrological groups C and D, which have a very low permeability. This means that a large volume of rainfalls converts into runoffs. Due to the low permeability and the vicinity to the watershed outlet, the northern half, especially in the northwest of the watershed, has a very high runoff depth and height. Also, the flood risk is high in Lavijrood River route and its surrounding area especially at the downstream. The runoff simulation in this watershed showed that land use, soil, permeability, slope, and the geographical distribution of rainfalls are the most important factors that control runoffs and their movement to downstream locations to produce floods