Drainage infrastructure under scrutiny: economic and operational evaluation of sustainable and grey systems based on rainfall time series

ABSTRACT Stormwater management is essential to safeguard communities, ecosystems and the environment from floods. Although SuDS on hypothetical and conceptual catchments are available in the literature, feasible and integrated systems based on large real-world urban catchments are lacking. Also, failure to incorporate economic analyses considering life-cycle costing is inveterate, and systemic omission of maintenance costs at project inception distorts life-cycle economics, misguides policy priorities and accelerates infrastructure aging and disrepair through neglected upkeep. Therefore, this article evaluated the life-cycle costs and operational performance of grey drainage infrastructure and SuDS in a large urban catchment on a greenfield site of 17.67 acres, for a proposed residential development comprising 780 dwellings across 52 three-storey blocks. Rainfall time series with multiple storm scenarios were developed for the drainage infrastructure design and post-design hydrologic and hydraulic simulations. The operation and maintenance costs contributed over 35% of the total drainage infrastructure cost, demonstrating the fundamental importance of life-cycle costing at project inception. The research found that the SuDS design standards were lagging. Additionally, the combination of fixed safety allowances in the design standards and probabilistic rainfall modelling resulted in overdesign and high marginal costs. The SuDS achieved runoff attenuation regulatory compliance and represented superior economic value.