Brisbane City Hall Green Parking Lot


The landscaped area in the Brisbane City Hall parking lot is actually an engineered system for treating stormwater runoff. This area, called a rain garden or bioretention area, collects stormwater runoff from both the parking lot and building roof. Runoff is treated as it filters through the specially-selected vegetation and soaks into the ground. Drain lines buried in the rain garden (the underdrain system) collect the treated water and send it through the City's stormdrain system to Brisbane Lagoon and out into the Bay.
The rain garden uses a special soil mixture to help runoff soak into the ground and plants that do well in wet conditions.

The bioswale along Valley Drive also collects and treats stormwater runoff.

Another stormwater treatment system, called a bioswale, is located on the opposite side of City Hall along Valley Drive. In this system, parking lot and roof runoff is treated as it gradually flows along the length of the bioswale, being filtered by the grass and soaking into the ground before reaching the City's storm drain system and flowing to Brisbane Lagoon and out into the Bay. These treatment systems help keep pollutants from our cars out of the Bay.

The underdrain system beneath the rain garden carries treated stormwater runoff to the Brisbane Lagoon and out to the Bay.

During very heavy storms, runoff ponds up and eventually overflows into the storm drain inlet to prevent flooding.