A Novel and Practically Applicable Simulation–Optimization Framework for River Cross-Section Modification: Integrating the HEC-RAS Simulation with the Grasshopper Optimization Algorithm

Enhancing river cross sections is one of the most critical structural measures to regulate flow and mitigate flood damage. Given the importance of cost control in river engineering projects, this study integrates hydraulic simulation with metaheuristic optimization to develop a new and practically oriented framework for cost-effective river cross-section modification to reduce losses from flooding. The Zayanderud River in Iran was simulated using a digital elevation model and the RAS Mapper tool in the Hydrologic Engineering Center’s (HEC) River Analysis System (HEC-RAS) software to extract cross-section geometry and flow characteristics. A new objective function was then formulated that simultaneously considers dredging costs and flood loss mitigation. Using this function, the grasshopper optimization algorithm (GOA) was employed to optimize river cross sections under a 50-year flood return constraint. To demonstrate robustness, GOA was benchmarked against the gray wolf optimizer, genetic algorithm, and particle swarm optimization. Results confirmed the superiority of GOA, which reduced optimization time by 50% (500 iterations) and achieved the lowest dredging cost of $15,578 for a 200-m segment—3.55% to 17.80% lower than competing algorithms. Importantly, the present approach prevented incurring damages amounting to 35.14 times the dredging cost. Furthermore, the hydraulic simulation improved the accuracy of the optimization, leading to an 8.29% additional cost reduction. Such savings are substantial in real-world river engineering projects, contributing to effective flood control and reduction of flood-related damages and demonstrating the practical applicability of the proposed methodology for stakeholders seeking cost-effective yet hydraulically feasible solutions.