Green infrastructures and their impact on resilience: spatial interactions in centralized sewer systems

Resilience in urban drainage infrastructure management has gained traction in the last few years, where systems need to adapt and recover from failure in face of deep uncertain threats. Green infrastructures, on-site nature-based stormwater strategies, are a promising concept that has proven to be effective in increasing the overall resilience performance in sewer systems. However, the improvement is not always significant or guaranteed. There is a lack of understanding of the local effects of these infrastructures and the spatial components of the impact on resilience in the network. In this work, the spatial interactions between GI placement and improvements in the centralized sewer networks resilience were studied, whilst considering a wide range of design storms. Resilience is assessed using two metrics: flood volume and flood duration. The scenarios simulated were baseline scenarios with no green infrastructure for each rainfall (scenarios type 1) and a placement scheme using critical component analysis (scenarios type 2). The spatial interactions were analysed through three main points, the magnitude of the impact, the number of affected nodes and the location of the impact in the network. This analysis was applied in a case-study in the United Kingdom. Regarding the magnitude of the impact, even though at a system level the impact is not high, at a node level the impact can be significant. Also, the impact is higher in shorter duration and lower return period storms. Regarding the number of affected nodes, most of the nodes remain unchanged. When all the scenarios are considered, there are as many nodes with an increase, as there are with a decrease in flooding volume and duration. Regarding the location of the impact, the nearest nodes to the outlet show the highest reduction in flood volume and flood duration. Subcatchments upstream the network and with highest areas seem to be the most impactful in the flood volume change. For flood duration, the subcatchments with smaller areas and generally in a middle region in the network cause the highest changes. This study is a first approximation to understand spatial considerations regarding the impact on resilience based on different green infrastructure location in the network.