Modelling Infiltration Systems' Performance for Efficient, Sustainable or Circular Urban Water Drainage

A typical infiltration system (IS) consists of an urban sub-catchment that works in synergy with an engineered pervious sub-catchment (e.g., a trench). ISs for sustainable urban drainage meet multiple design objectives: returning water resources to the environment (circularity) and reducing hydraulic risk. ISs, by necessity, are realized in the public spaces which belong to historical city centers, industrial zones, densely populated urban areas or areas of recent urbanization. Available space conditions the shape of impervious drainage sub-basins and downstream trenches that hold and release runoff volume to the subsoil. Catchment shape and rainfall intensity have received relatively less attention in the designing and decision-making processes than rainfall volume. A hydrodynamic model (HM) offers the opportunity to systematically investigate the efficiency of ISs as shape and rain intensity change, overcomes the limits of the widespread bucket modelling approach, which is narrowly focused on rain volume, trench storage capacity and exfiltration capacity, and links the shape of IS to its efficiency and to the residual risk that occurs when events of intensity greater than the design event occur. The results of a systematic sensitivity analysis, conducted by the use of HM, suggest new criteria for evaluating whether ISs are suitable for achieving the design objectives, within the constraints of the available urban public space.