Water Sensitive Urban Design
Traditional urban development alters landscapes surfaces from being permeable to water so that they become impermeable. This causes large stormwater runoffs with harmful impact on the environment by soil erosion and by carrying suspended solid pollutants into lakes, creeks, rivers and the ocean. A major source of pollutants in the Derwent Estuary is stormwater runoff from urban development.
Water sensitive urban design (WSUD) seeks to reduce this pollution from suspended solids. We aim to limit the environmental impact of North Bay so as to protect our Saltmarsh, Ralphs bay and the Derwent river. We now have two Swales. We achieve this by a variety of WSUD measures.
The grassed areas overlie a bed of sand and deep to that porous stormwater drains. This is a filtering mechanism removing suspended solids from stormwater.
We build rain gardens which are similar to Swales but use shrubs as well as grass.
Domestic water tanks are mandatory in North Bay and these reduce stormwater runoff. In addition they save the homeowner money by reducing water bills. Alone this measure reduces stormwater runoff by 25%.
We are now constructing a freshwater wetland near the stormwater outfalls to further clean the runoff.
None of these measures are planning requirements and they do add significant cost to the development.
A Swale at North Bay
How a Rain Garden Works
Rain Garden at North Bay
Building a Swale
This is the continuation of the swale in Enchantress Street below. The second photo shows an agricultural drain being laid. This picks up water that has soaked through a sand layer below the lawn that will be planted on the surface. This mechanism purifies storm water prior to discharge into the river by filtering out the suspended solids, the main pollutant in storm water.