Flood is a common natural disaster that causes immense damage to the natural environment, construction and casualties worldwide every year. The control factors of the flood are power, magnitude, and frequency, duration of the flow and changes of cross-sections. In this research, the quantitative fringe of Gamasiyab River (located in the Kermanshah province) has been investigated using DLSRS model. The DLSRS is the first mathematical model for calculation of quantitative fringe according to the rules and regulations of the country. First, the cross-sections were extracted by the HEC-GeoRAS extension in GIS software. Then the quantitative fringe of Gamasiyab River has been calculated for 130 cross-sections by five indexes including discharge (25 years return period), location of the river, stability of the bed and bank, flow regime and social tension. The results of the model show that the quantitative fringe was 3 to 13 meters on average in different reaches so that the highest value of the fringe in the Gamasiab River was in the reach 1 and the lowest was in the reach 11. Also results show that this model was not suitable for all of the rivers in the country and it is suitable for the rivers that have different stream orders. Therefore the results of this model will not be acceptable for the Gamasiyab River (the stream order of this river is 5th). This model is suitable for the rivers which have bare and non-proprietary riparian.

Introduction The main purpose of this research is to identify the behavior of rivers in the area of Lashtghan shrimp breeding site and to provide technical solutions to organize and prevent flood risks there.   Materials and methods In this study, HEC-RAS was used to perform hydraulic flow calculations based on unsteady flow. Calculations were done with changes in flood flow with different return periods. To determine the flood zone for the 25-year return period, the water height was transferred to ArcGIS. Using the HEC-Geo-RAS extension, the flood zone was determined in ArcGIS. To present the proposed natural bed line, satellite images at different time intervals were analyzed and the proposed bed line was extracted after verifying the flood zone with these images. The amount of technical protection was calculated using the DLSRS (Discharge Location Stability Regime Social Tension) method. The flood return period for the design was considered to be 100 years, based on economic, social, and climatic conditions. Considering the project's purpose, domain of usage, and technical and economic conditions, an earthen dike was selected for the land protection plan against floods. In Civil 3D software, the protective dike project line was defined and, according to the 100-year flood water level, the protective dike was designed.   Results and discussion The boundary for modeling the flow of rivers and canals leading to the Lashtghan site was established upstream of the hydrograph and downstream of the water level (2.9 meters, or 76% of the duration of the course is less than this value), based on justification studies. The observed minimum height is approximately 0.65 meters, the maximum height is 5.7 meters, and the average height is approximately 1.6 meters; these measurements are insufficient to ascertain the height of the dike. The height reached its highest and lowest values every six hours. In the northern region of the site, the maximum water level, maximum flow depth, and maximum flow speed were more apparent. The water level fluctuated between 1.2 and 35 meters, the maximum flow depth increased from 0.001 to 40 meters, and the maximum flow velocity improved from 0.00033 to 1.8 meters per second.   Conclusion The model output included characteristics of the maximum flow level, depth of flow, and maximum flow velocity in the study area. It was observed that the built dike has no effect on the surrounding residential areas. Due to the topography, the earthen dike acts like a reservoir in some places, preventing downstream flow and storing water behind the dike. This reservoir has a volume of about 3 million cubic meters for a 100-year return period flood. By constructing a borrow pit near the dike, a significant part of the water can be transferred downstream. Finally, the height of the dike, the slope of the body, and the width of its crown were calculated, with the cost estimated at 72,925,000,000 million Rials.