Water Sensitive Urban Design

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Water Sensitive Urban Design 3 | Attainment of the Stormwater Quality Targets Figure 1 - Examples of bioretention systems in planter boxes, in parks and in the streetscape Stormwater quality targets can be met through stormwater treatment systems, such as bioretention systems, swales and wetlands. Landcom’s stormwater pollution reduction targets require a 45% reduction in the mean annual load of total nitrogen, 65% reduction in the mean annual load of total phosphorus and an 85% reduction in the mean annual load of total suspended solids. The stretch targets are for stormwater pollution load reductions are of 65%, 85% and 90% respectively. Stormwater quality targets can be met through stormwater treatment systems, such as bioretention systems, swales and wetlands, which can be incorporated into public open space, streetscapes or on lots. Further information on these devices is contained within the NSW Government document Managing Urban Stormwater: Treatment Techniques. 3.1 Bioretention Systems Bioretention systems filter stormwater runoff through a vegetated soil media layer. The treated stormwater is collected at the base of the system via perforated pipes, from where it flows to downstream waterways or storages for reuse. Temporary ponding above the vegetated soil media provides additional treatment. Bioretention systems are not intended to be infiltration systems where treated stormwater would discharge into groundwater. Typically flood flows bypass the system thereby preventing high flow velocities that can dislodge collected pollutants or scour vegetation. Bioretention systems can be installed at various scales, for example, in planter boxes, in parks or in streetscapes integrated with traffic calming measures. (Figure 1). 3.1.1 Street trees Recovery Pipeline Porous Pavement Filtration Media Street tree bioretention systems are small bioretention systems that take the place of traditional street trees. These systems can be integrated into high-density urban environments and can take on a variety of forms (Figure 2). A typical arrangement of a street tree bioretention system is shown above. The filtration media should be at least 0.8 m deep to allow for root growth of the tree, therefore substantial depth is required between the inlet and outlet. 14 Book 2 | planning and management
Water Sensitive Urban Design Figure 2 - Example of street tree bioretention systems Figure 3a - Example of bioretention raingarden Raingardens can be incorporated in a range of locations, as they can be any shape and size. 3.1.2 Raingardens Example raingarden concept design Temporary ponding Growing Media (filter) 1:6 Perforated under drain Geofabric Overflow Pit Vegetation Raingardens can be incorporated in a range of locations, as they can be any shape and size. Typical locations include pocket parks, traffic calming measures and between parking bays. Examples and a typical raingarden arrangement is shown in Figures 3a & 3b. g Pipe 0.15m 0.8m minimum if tree planted 0.2m (drainage layer) 3.1.3 Bioretention swales Swale bioretention systems provide both stormwater treatment and conveyance functions. A bioretention system is installed in the base of a swale, whereby the swale provides stormwater pretreatment to remove coarse to medium sediments. The bioretention system can be installed in part of a swale, or along the full length of a swale, depending on treatment requirements. Runoff can be directed into conveyance bioretention systems either through direct surface runoff (eg. with flush kerbs) or from an outlet of a pipe system. An example of these systems is shown in Figure 4. 0.2-.5 m 1-3 m 0.3-0.7 m Filter media (sandy loam) Perforated collection pipe Possible impervious liner 0.1 m 0.15-0.2 m Transition layer (coarse sand) Drainage layer (coarse sand/ gravel) 0.6-2.0 m Figure 4 - Example of bioretention swales Book 2 | planning and management 15
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Water Sensitive Urban Design

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