Performance Evaluation of Topographical-based HAND in the Estimation Flood Inundation Maps

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Introduction: Floods are a natural disaster that threatens the lives of millions of people every year. Obtaining the flood zone and consequently obtaining the flood zone map for current with a specific return period for a desired basin is one of the important results obtained from different models. Therefore, extraction of flood zone is one of the basic needs in the design of water structures, a basic step for management and planning to reduce economic and social flood damage, use to determine the amount of insurance for residential areas along the river and also identify high risk areas of the river In terms of flood status and flood control measures. Evaluating the performance of the HAND model, which relies solely on topographic features, is one of the objectives of the present project. Methodology: In this study, the flood zone is determined using the HAND model with a calibrated coefficient of roughness. Seymareh River has been selected as a study area to challenge the performance of the model in relation to the observational data obtained from satellite images and also to evaluate it with the HEC-RAS hydraulic model. Also, the HAND model in low and high flows has been evaluated with a 1D and 2D hydraulic model to evaluate the performance of the model in different flow conditions. Results and Discussion: In the first part, the HAND model was evaluated using satellite images, which show the very good performance of the model in determining the flood zone. Further sensitivity analysis of Manning roughness coefficient showed that increasing and decreasing it by 25% had no effect on improving the performance of the HAND model and the roughness coefficient was properly calibrated. Finally, the model was evaluated with 1D and 2D hydraulic model in low and high input flow conditions. The results showed that the HAND model still has a good capability in comparison with hydraulic models in different flow conditions. Conclusions: The most important results can be summarized as follows: • The results obtained from the HAND model based on the calibration coefficient calibrated in Seimareh river indicate the proper performance of the model in obtaining flood zone. According to calculations, the rate of flood zone adaptation is higher than 92% compared to satellite images. Also, the average difference between the HAND model and satellite images for estimating flood zones during the study period of the river was about 8.5%. The occurrence of turbulence and rotational flows due to improper angle of connection between the channel and the freeway bridges in the future will have a significant impact on the hydraulic flow and sediment of the river, especially in the area of the bridges. • The results in Seimareh River show that increasing and decreasing the inlet flow does not change the performance results of the HAND model and also the model has a good capability compared to hydraulic models. According to calculations, the rate of adaptation of the flood zone in comparison with the hydraulic model in different discharges is always higher than 83%. Also, the average difference between the HAND model and hydraulic models for estimating flood zones during the study period of the river will be less than 13%. • Despite the very good performance of the HAND model in estimating the flood zone, in some intervals there are differences between the HAND model with satellite images and the hydraulic model, which can be done by using topographic maps with high resolution and river path inter Extraction of Rating-curves for each substrate greatly enhances the performance of the HAND model. • Hydraulic model has more error in estimating flood zone than HAND model. The main reason for this can be related to important factors such as: distance between cross sections, computational cell dimensions, numerical parameters used in the 2D hydraulic model (such as θ parameter and currant number), boundary conditions used in the hydraulic model Calibrate the time step and determine the Manning roughness coefficient for each cross section. In general, relatively more factors affect the performance of the hydraulic model and affect its output, while the HAND model experiences relatively better conditions in this regard, so that only by considering a coefficient of roughness for the whole The study interval and extraction of the Rating- curve can be used to obtain the flood zone. while the HAND model experiences relatively better conditions in this regard, so that only by considering a coefficient of roughness for the whole The study interval and extraction of the Rating- curve can be used to obtain the flood zone.