Evaluation of hydrogeomorphometric parameters of Bastam watershed with emphasis on flooding

Problems of watersheds and their water resources require comprehensive planning and integrated management in this natural open system, which is necessary to be prioritized in national and regional plans to achieve the sustainable development goals, flood risk and crisis management, and solving water shortage issues. Purpose of this research is the evaluating and analyses of hydrogeomorphometric components in Bastam watershed systematically to understand environmental, flood and erosion issues. In this regard, parameters of the height distribution, average height, altimetry and hypsometry curves, slope, aspect, watercourse rating, branching ratio, drainage density, watercourse boundary, main watercourse length, concentration time, perimeter, area, basin shape, Gravilius coefficient and equivalent rectangle was evaluated. Results showed that study basin with an average height of 2085.341 meters and an average slope of 21.788% is a mature and relatively smooth basin, and its upstream slopes at altitudes of more than 2100 meters are exposed to exploration due to the roughness youth. Maximum extent of the basin with 24.53% belongs to the southeast aspect. Shape of the basin is like a rectangle with a length of 91.842 km and a width of 19.175 km, which has a medium to small flood capacity. Components of branching ratio 3.528, drainage density 0.2985 and compression coefficient 0.09352 indicate the low to moderate flooding of this basin. Its concentration time in the main waterway with a length of 62.675 km is equal to 6.066 hours, which has the maximum flood with 6-hour rains.