A novel framework for prioritization and spatial suitability assessment of Blue-Green infrastructure for urban pluvial flood resilience

Abstract

Blue-Green Infrastructure (BGI) is amongst the most promising solutions to urban pluvial flooding. Optimum siting of BGI for maximum efficiency based on demand–supply assessment is a challenging problem investigated by earlier researchers. However, risk-based demand assessments focus on system vulnerabilities and often overlook the inherent system capacity to absorb and adapt to floods. A more effective approach would involve a resilience-based need assessment to optimize the use of available resources for maximum efficiency. In this research, a resilience-based framework is developed for BGI spatial planning in four modules to prioritize areas requiring intervention, assess spatial suitability, validate and optimize the proposed BGI. In Kochi City of Southern India, indicators of Normalized Difference Vegetation Index, Normalized Difference Water Index, Topographic Wetness Index, Soil Potential Retention, and Patch Cohesion Index are weighted and applied for prioritization using weighted overlay analysis. Spatial suitability is assessed using land-use classification, plot size, and accessibility. A decentralized detention storage facility is proposed as the optimum BGI for the city which is simulated for a 24-hour event with a 25-year return period using Personnel Computer Storm Water Management Model (PCSWMM). ‘Duration Factor’ is examined to understand the effect of flood duration and depth on the city’s functionality. The sizes of BGI facility are optimized using non-dominated sorting genetic algorithm. The results of the flood modelling indicate a significant reduction in average flood duration by around 24% and flood depth by around 28% with the detention storage system, which is further improved by the optimization of detention storages sizes. Key contributions of this study are a methodological framework for site prioritization, suitability mapping, and a typological classification for small to medium-scale urban flood storage facilities. The proposed framework has important implications in identifying, prioritizing, optimizing and placing BGI for improved urban flood resilience.