This study presents the design and optimization of the grade line for stormwater drainage pipes installed under the side ditches of Aliartos town bypass road, Greece. The project focuses on optimizing the excavation depth, which is directly related to construction cost, while adhering to constraints on the maximum and minimum allowable pipe depths. The slope of the pipes must be downhill and confined within specified limits to ensure efficient drainage performance. A custom optimization framework was developed, designed to be compatible with standard optimization routines available in Matlab. The formulation of this problem posed unique challenges due to the multiple constraints and the need for a robust solution methodology. Various optimization algorithms, including Simulated Annealing and Particle Swarm Optimization, were evaluated to identify the most effective and computationally efficient approach. The proposed method was used on the design of 69 pipes along the Aliartos bypass, resulting in highly satisfactory performance. The optimized pipe grade lines demonstrated significant reductions in excavation depth while ensuring compliance with depth and slope requirements. The results confirm the effectiveness of the chosen optimization technique, offering a reliable and cost-efficient solution for similar stormwater drainage projects.