This paper discusses numerical modelling approaches for three different types of measures commonly used in the Netherlands: green roofs, swale filter drainage systems (swales), and infiltration-transport drainage systems (IT-drains). A combination of physically based and empirical formulae as well as urban hydrologic and hydraulic modelling software was used to assess the effectiveness of the measures.

The analysis has shown that these systems are promising, especially at the scale of the individual measures (a single IT-drain pipe, swale or green roof). Due to non-linearity issues, the up-scaling of such measures to city and neighbourhood levels remained a challenge, thus further research is required. The modelling concepts for green roofs and swales were applied in a synthetic case study to illustrate the possible effects of SUDS on the reduction of inundation volumes in urban areas. The case study consisted of an imaginary urban area with properties resembling average urban areas in the Netherlands.

These storm water infiltration systems have been developed to reduce flooding risk or to increase groundwater recharge. As a consequence, software modelling for urban drainage systems enabled water authorities and municipalities to assess the impact of sustainable urban drainage measures ‘SUDS’ on local flood hazards.