From design intent to operational performance: monitored evidence from three stormwater attenuation systems

ABSTRACT This article evaluates what different monitoring configurations can reveal about the operational performance of stormwater storage assets across neighbourhood, household, and site scales. Three proof-of-concept sustainable drainage systems and stormwater storage trials in southern England were analysed: slow-drain leaky tanks at Havenstreet, smart and leaky rain tanks in Deal, and a below-ground attenuation tank at the University of Exeter Sportspark. The analysis used rainfall, spill occurrence, tank water depth, overflow thresholds, and monitored water-level records to assess rainfall-response behaviour, storage activation, overflow occurrence, drawdown, and indicative storage utilisation. At Havenstreet, pre-intervention spills were most clearly associated with short-duration rainfall intensity, while no spills were observed during the short post-installation period considered. At Deal, smart tanks maintained storage availability more effectively than leaky tanks, with two smart systems recording no overflows during the monitoring period, while leaky systems recorded frequent overflows and blockage issues. At Exeter's Sportspark, monitoring confirmed active filling and drawdown, with the peak calculated water depth reaching 98 mm, equivalent to 8.2% of the recorded 1.2 m tank depth. Across the three case studies, the strength of performance interpretation depended on both the monitoring data collected and the availability of supporting asset information, including contributing area, storage geometry, reference levels, control characteristics, and operational condition. The cross-case synthesis indicates that monitoring can reveal operational behaviour not apparent from design information alone, while progressively stronger storage and hydraulic assessment requires more complete supporting asset data.