Introduction and Objective: The main objective of this article is to simulate the hydraulics of the Haraz River and the impact of floods with different return periods on fish farms along the river and to investigate the risks and consequences of their occurrence, so that flood-resistant farms can be designed in this way. It identified the riverbed and boundary and provided assistance in flood warning systems for necessary measures to reduce potential losses. Flood risk assessment and management of potential loss reduction require hydraulic simulation of river flow, and by identifying fish farms at risk, solutions can be provided to reduce flood damage with different return periods.
Materials and Methods: Haraz River is one of the three permanent and high-flowing rivers in the north of the country, and its average flow rate is 40 m³/s. Due to access to suitable water, more than 30 cold-water fish farms are operating upstream and on the banks of this river, which has the largest share of cold-water fish production in Mazandaran province in terms of number of farms and production rate. The highest density of fish farms is in intervals 1, 2 and 3. In the present study, an analysis method based on the integration of HEC-RAS and the geographic information system GIS has been used in the study of flood risk. This method involves the use of geomorphological, topographic, boundary and hydraulic data. The results obtained from this method include the preparation of flood depth and area maps and provide valuable information for reducing flood risk. Using ArcMap software, a digital elevation model with a resolution of 2 meters was prepared for the three study intervals that had the highest density of fish farms on the banks of the Haraz River. The maps were drawn in the GIS software environment and the hydraulic model was prepared in the HEC-RAS 6.5 software. Using the RAS Mapper section of the HEC-RAS model subprograms to separate the main river channel from its banks, the river banks layer was drawn and then the flow path dimensions layer was prepared. This layer was used to determine the dimensions of the hydraulic flow path in the main flow channel and its left and right banks in the floodplain area. The main key to flood simulation is the cross sections, which were drawn in the direction of flow, perpendicular to the flow path from the left bank to the right bank. In order to analyze the flow, the discharge values ​​with return periods of 2, 10, 25, 50 and 100 years for the hydrometric station known as After the Spring received from the regional water reports of Tehran province and the Manning roughness coefficient values ​​of the bed and walls were used from the reports of the Mazandaran Provincial Regional Water Company.
Findings: In the HEC-RAS model, parameters such as water level, including the outlet of cross sections, the longitudinal profile of the river, changes in water velocity in all sections and the discharge-shear curve and hydraulic characteristics of the flow in different return periods were obtained. The expanded area of ​​the floodplain on the fish farms along the Haraz River in the study periods was calculated using GIS software according to the discharge with return periods of 2, 10, 25, 50 and 100 years. The results showed that more than 60 percent of the fish farms along the Haraz River are at risk of flooding with different return periods. According to the results, the risk of a 25-year flood was about 29.5 percent and a 100-year flood was 33.3 percent, which makes flood control necessary to reduce losses.
Conclusion: The results obtained indicate the high efficiency and sensitivity of the HEC-RAS hydraulic model for flood zoning. By using GIS and HEC-RAS software, the depth, flood velocity, and floodplain areas can be obtained in different locations.