Stormwater Management and Water Sensitive Urban Design

About this course.

Stormwater management matters because rain that falls on a developed site, if not properly controlled, causes harm well beyond that site: it can flood the property and its neighbours, erode land and drainage channels, and carry sediment and pollutants into the creeks, rivers, wetlands and bays that ultimately receive it, degrading their health. Development makes this worse by replacing absorbent ground with hard, impervious surfaces, so more rain runs off, faster, than the land would naturally shed. Responsibility for regulating stormwater is shared and varies by location: local councils typically control drainage and development requirements, water authorities may manage larger drainage and waterway assets, and environmental regulators oversee pollution of waterways. Because these arrangements and their rules differ from place to place, requirements must always be confirmed for the specific site.

To understand the problem, start with what development does to the water cycle. On undeveloped land, a large share of rainfall soaks into the soil, is taken up by vegetation, or evaporates, and only a portion runs off, slowly, into natural drainage lines. When a site is developed, roofs, paving, driveways and compacted ground replace soil and vegetation with impervious surfaces. Water can no longer soak in, so far more of it runs off, and it runs off faster because smooth hard surfaces and piped drainage speed its journey. The result is a larger volume of runoff arriving more quickly and with sharper peaks than the natural catchment ever produced. Multiplied across a whole suburb, this transformation is why urban areas are so prone to the drainage problems that stormwater management exists to address.