Multiobjective optimisation and cluster analysis in placement of best management practices in an urban flooding scenario

Abstract

This research is being carried out to study how best management practices (BMPs) can mitigate the negative effects of urban floods during extreme rainfall events. Strategically placing BMPs throughout open areas and rooftops in urban areas serves multiple purposes of storage of rainwater, removal of pollutants from surface runoff and sustainable utilisation of land. This situation is framed as a multiobjective optimisation problem to analyse the trade-offs between multiple goals of runoff reduction, construction cost and pollutant load reduction. Output includes a wide range of choices to choose from for decision makers. Proposed methodology is demonstrated with a case study of Greater Hyderabad Municipal Corporation (GHMC), India. A historical extreme rainfall event of 237.5 mm which occurred in 2016 and extreme rainfall event of 1,740.62 mm corresponding to representative concentration pathway (RCP) 2.6 were considered for analysis. Two multiobjective optimisation algorithms, namely non-dominated sorting genetic algorithm-III (NSGA-III) and constrained two-archive evolutionary algorithm (C-TAEA) are used to solve the BMP placement problem, following which the resulting Pareto-fronts are ensembled. K-Medoids-based cluster analysis is performed on the resulting ensembled Pareto-front. The proposed ensembled approach identified ten possible BMP configurations, with costs ranging from Rs. 4:30 × 109 to 2:08 × 1010, surface runoff reduction ranging from 0:37 × 107 m3 to 1:45 × 107 m3, and pollutant load removal ranging from 25:5 tonnes to 99:8 tonnes. Use of BMPs in future events has the potential to reduce surface runoff from 0:13 × 108 m3 to 1:08 × 108 m3, while simultaneously removing 42:4 to 305:4 tonnes of pollutants for cost ranging from Rs: 0:20 × 1010 to Rs :2:10 × 1010. The proposed framework forms an effective and novel way to characterise and solve BMP optimisation problems in context of climate change, presenting a view of the urban flooding scenario today, and the likely course of events in the future.