Determination of design flow rate for flood control according to economic criteria

Flood is one of the most effective naturel disasters. The magnitude and the frequency of floods are essential for designing hydraulic structures. Floods are the most complicated problems of engineering hydrology. Therefore, the characteristics of project floods must be determined accurately in order to build reliable hydraulic structures.The relation between the characteristics of a flood and the areas that may be effected from it must be studied in detail as floods are the reason of the serious damages and losses in our country and in the most parts of the world. A detailed study on floods and flood zones requires the time and spatial analysis of hydrological, hydraulic, topographic and other related factors. Recently, modeling techniques for the determination of flood zone are widely used to observe the place of flood and its frequency. By virtue of this method flood predictions can be made more quickly and more accurately and the borders of the flood zones observed more precisely.In this study, using hydraulic and hydrologic modeling softwares, flood risk analysis are performed on Karacaali Creek which is one of the branches of Küçükmenderes River Turkey. Flood risk maps are obtained and the optimum frequencies of flood control discharges determined by using three different flood control method.In this study, modeling of topography and presentation of results are performed on ArcGIS 9.3.1 and hydrologic analyses undertaken by using Hydrologic Engineering Centers River Analysis System (HECRAS) 4.1. Topographic data that develop terrain surface are assured from 1/25000 scale maps that belong to Turkish General Command of Mapping and utilized in the study of protecting agricultural terrains of Tire district from floods of Karacaali Creek performed by General Directorate of State Hydraulic Works (DSI). In this way 3D model of terrain is created by using ArcGIS. All topographic data taken from this model is transferred into HEC-RAS by the HEC-GeoRAS module that is executed on ArcGIS. Discharge rates that have various frequencies are carried from Mockus method. By this way water levels are determined as a result of entering discharges to the model. The flood risk maps are obtained after the results into ArcGIS by HEC-GeoRAS.Under various flood circumstances, total damage loss is calculated by transferred taking into account of vegetation pattern of agricultural lands to be impounded according to flood risk maps. To control those floods, various structures such as rock lined embankment with toe berm, trapezoidal earth channel and rock lined trapezoidal channel are designed as different exercises having estimating the construction cost of each structure minimum value of summation of annual average damage loss and annual project cost of option is determined to obtain the optimized project flood frequency. Finally recommendations are made to invoke further studies.