Evaluation of Optimized Zayandehrud River Channel Dimensions to Mitigate Flood Damage

To provide critical insights into the channel geometry characteristics and hydraulic behavior, a comprehensive hydraulic simulation was conducted using the Hydrologic Engineering Center—River Analysis System (HEC—RAS) software. This analysis focused on the Zayandehrud River in Iran, aiming to enhance flood prevention and mitigate potential damage. As an innovative methodology, the calibrated HEC—RAS results were integrated with the Areal Difference Asymmetry Index (ADAI) and optimal geometric equations to derive the optimized dimensions of the river cross‐sections. After achieving optimal geometric parameters, such as width, depth, hydraulic radius, wet perimeter, bank profile, and areas, the optimum cross‐section indices (OCIs) were applied. This index quantified the numerical value of each river cross‐section relative to its optimal condition, enabling a comprehensive evaluation of cross‐sections based on their degree of optimization. On the basis of the watercourse assessment, the river width increased by 346.98%, whereas the depth decreased by 22.94% from upstream to downstream, and the downstream cross‐sections were more symmetrical than the upstream cross‐sections. The area of the calculated optimal cross‐sections gradually increased toward the downstream and was far from the optimal geometry. The increase in values of OCIs, ranging from 5% to 120% from upstream to downstream, indicated a greater need for channel modification in the downstream reaches.