DRAINS is a multi-purpose Windows program for designing and analysing urban stormwater drainage systems and catchments. DRAINS can model drainage systems of all sizes, from small to very large (up to 10 km2 using multiple sub-catchments1 with ARR 2016 and ILSAX hydrology, and larger using storage routing model hydrology). Working through a number of time steps during the course of a storm event, it converts rainfall patterns to stormwater runoff hydrographs and routes these through networks of pipes, detention basins, channels and streams. In this process, it integrates:

• design and analysis tasks,
• hydrology (five alternative models) and hydraulics (two alternative procedures),
• closed conduit and open channel systems,
• headwalls, culverts and other structures,
• stormwater detention systems, and
• large-scale urban and rural catchments.

Within a single package, DRAINS can carry out hydrological modelling using ARR2016, ILSAX, rational method and storage routing models, together with unsteady hydraulic modelling of systems of pipes, open channels, and in the premium hydraulic model, surface overflow routes. It includes an automatic design procedure for piped drainage systems, connections to CAD and GIS programs, and an in-built Help system.