Optimization of urban stormwater systems: a multi-criteria approach to sustainable and cost-effective LID implementation

Rapid urbanization has dramatically increased impervious surfaces, exacerbating flood risks in cities globally. Low-impact development (LID) practices are effective in reducing urban runoff, but selecting optimal combinations based on cost, performance, and service benefits remains crucial. This study presents a comprehensive framework for optimizing urban stormwater management by integrating a simulation-optimization module, which consists of stormwater management model-SUSTAIN models, with a multi-criteria decision-making module. To guide decision-makers, it introduces two novel criteria - sustainability index, derived from reliability, resiliency, and vulnerability indices, and vegetated LID coverage to account for LID's extra environmental benefits such as air quality improvement and aesthetics, alongside cost. The proposed methodology is applied to Tehran's District 11, where four LID scenarios, including green roofs (GR), rain barrels (RB), bioretention cells (BC), porous pavements (PP), and vegetated swales (VS), are evaluated using the WASPAS method. Scenario 2 (RB, BC, and VS) is identified as the most favourable due to its cost-effectiveness, even though it has lower vegetated LID coverage than two of the other scenarios. This study offers a practical tool to balance multiple objectives in urban stormwater system design and management, promoting sustainability and cost-efficiency.