Stormwater Management in Illawarra

Stormwater management is the planning, design, installation and ongoing maintenance of systems that collect, control and safely dispose of rainwater runoff from roofs, driveways, paved surfaces and landscaped areas. In Illawarra, stormwater management is particularly critical because the region receives 1,200-1,400mm of annual rainfall with intense coastal storms capable of delivering 50-100mm in a single event. A properly designed stormwater system includes roof gutters and downpipes feeding into underground stormwater pipes (minimum 90mm diameter for residential), stormwater pits or junction boxes at collection points ($800-$2,000 installed), pipe runs graded at minimum 1:60 fall connecting to the street kerb, council easement or natural watercourse ($1,500-$5,000), and where required by council, on-site detention (OSD) tanks that temporarily store peak runoff and release it at a controlled rate ($3,000-$8,000). Illawarra councils — Wollongong City Council, Kiama Municipal Council and Shellharbour City Council — each have specific stormwater management requirements for development applications. New homes typically require a stormwater management plan showing how runoff is collected, conveyed and discharged without increasing flow to neighbours or downstream properties. Properties with inadequate stormwater management experience yard flooding, foundation undermining, retaining wall failure, driveway erosion, and disputes with neighbours receiving redirected runoff. Complete stormwater management systems for new Illawarra homes cost $5,000-$15,000 depending on site conditions, pipe run length and council requirements.