Design features.

This study introduces an integrated urban flood mitigation framework specifically tailored for Andean valley cities with complex river systems and steep topography, addressing a critical gap in hydrodynamic modeling for such challenging urban watersheds. Through a case study in Loja, Ecuador, high-resolution topographic surveys, distributed hydrological modeling (HEC-HMS), and two-dimensional hydraulic simulations (HEC-RAS) are employed to evaluate stormwater behavior across micro-watersheds for return periods of 10, 25, 50, and 100 years. The methodology informs the design of stormwater detention tanks, floodable parks, and parallel conduits to the existing U-shaped channel, forming a context-specific hybrid green-gray infrastructure strategy calibrated for extreme topographic gradients and constrained urban development patterns. Simulation results demonstrated the effectiveness of these interventions in preventing flooding under a 50-year return period and reducing flood-prone areas by 70% during a 100-year event. Importantly, this research introduces a transferable design framework for mountainous urban environments where conventional flood control is constrained by topography and land-use patterns. By integrating hydrodynamic modeling with scalable, low-footprint interventions, the approach offers practical solutions for climate-resilient urban planning in high-relief regions. This work contributes to Sustainable Development Goals (SDG 11.5, 11.B, and 13.1.1) by reducing flood-prone areas by 70% and protecting approximately 15,000 citizens. It further supports SDG 13 (Climate Action) through a 25.10% reduction in peak flow discharges, as demonstrated by hydrodynamic simulations. Limitations include assumptions inherent to static models and the absence of real-time hydrometeorological data. Future studies should incorporate sensor-based monitoring, refined climate projections, and economic assessments to enhance predictive capacity and long-term resilience planning.