Analytic hierarchy process in selecting Bioretention Cells in urban residential settlement: Analysing hydrologic and hydraulic metrics for sustainable stormwater management

This study aims at evaluating the role of bioretention cells (BRCs) in supporting sustainable stormwater management and reducing flood risk, focusing on urban residential settlements. For this purpose, an analytic hierarchical process (AHP) is employed to select the optimal BRC configuration (in terms of spatial settings and footprints). The optimal BRC spatial footprint is assessed for specific rainfall conditions and BRC spatial settings by considering 5 relevant criteria: the hydrologic (Volume Reduction - VR; Peak Flow Reduction - PR) and hydraulic metrics (Node Flooding Reduction - NFR; Network Stress Reduction - NSR) and the total cost. The modelling framework to evaluate the hydrologic-hydraulic metrics of the urban settlement is implemented by the TRIG Eau DST platform (http://www.trigeau.servergis.it/), a web-GIS based application that incorporates the SWMM v.5.1 (Stormwater Management Model). The simulation scenarios are defined based on five key variables: 4 precipitation regimes, 3 return times, 4 degrees of imperviousness, 2 BRC settings, and 4 BRC footprints, resulting in a total of 384 modelling scenarios. Simulation results, examined based on the hydrologic and hydraulic performance metrics, reveal that BRCs are effective in controlling runoff, with negligible overflow observed solely in limited cases. Furthermore, the BRC impact at the urban residential settlement is confirmed by the average values of the PR and VR ranging from 0.15 to 0.35 and 0.16 to 0.32, respectively. Focusing on the affecting factors, the impact of rainfall intensity on the effectiveness of BRC is moderate, whereas the degree of imperviousness has a significant effect. Findings of the AHP analysis demonstrate that for high precipitation regimes, BRC with 15% footprint is optimal, while BRC with a smaller footprint (equal to 10%) is more appropriate for low precipitation regimes. These results underscore the significance of strategic BRC placement and customization to improve the sustainable stormwater management practices in urban areas. Future research may incorporate other benefits of BRC (e.g., water quality metrics) as well as investigate a broader range of BRC designs (e.g., underdrains). The proposed methodology based on AHP analysis may support the implementation of sustainable urban drainage solutions (besides BRCs) within the existing urban areas.