Stormwater

The drainage systems within school facilities includes all the associated pipework and services for the removal and disposal of sanitary drainage and stormwater management in two separated systems. This section covers the Stormwater drainage system.

Refer to DG / DRAINAGE (& TRADE WASTE)

The stormwater drainage services is to be designed from a “Whole of Life” (WOL) perspective to provide:

• Value for Money
• Fit for purpose
• Long term reliability
• Minimal maintenance requirements
• Low maintenance costs
  Refer to DG / WHOLE OF LIFE
   
• Drainage is to be designed to prevent flash flooding entering into buildings and covered ways and to ensure that site facilities are available for students use in  all weather conditions up to a 1:100 ARI storm event.
• Design Drainage to channel stormwater away from buildings and facilities and to provide a backup system in case of blockages.
• Ensure that stormwater is designed to ensure the safety of students and staff.
• Design the stormwater system to compensate for movements in the foundations caused by moisture variations and subsidence.
• Ensure electrical pits and slabs beneath sprung timber floors, are graded to outlets connected to the stormwater system, to remove moisture/seepage. Incorporate reflux valves to prevent backflow.
• A Water Cycle Management Study is to be included with the design documents for all education facility developments. 
• Stormwater drainage is not to effect adjacent properties.
• Treat stormwater to remove foreign matter.
• Generally all underground drainage systems within the site area are to be CCTV inspected after installation and submitted as part of the work as executed submission.
• Avoid placing grated drainage pits to the centre of grassed free play areas where they can become a safety hazard.
• Support sustainable design principles including reducing water consumption and waste production.
• Appropriately treat any waste to ensure minimal environmental impact
• Be accessible and serviceable - easy to maintain with minimal impact on school use when maintenance is being performed
• Use products with a long life span – many drainage services are concealed so durability is essential.

• Design a reticulated primary inground piped stormwater and subsoil drainage system to collect and dispose of stormwater running onto and off the developed site.
• Design a secondary stormwater drainage overland flow system to safely and effectively dispose of stormwater, preferably over finished and natural ground, in the event of partial or complete blockage of the primary system.
• Design the inground drainage piped system for a 20 year ARI Storm event or to the requirements of the Local Council whichever is more severe. Provide above ground overland flow paths for 100 year ARI storm events in accordance to NSW Floodplain Management Manual (2001).
• Provide scour protection to head walls, pipe outlets and overflows.

Refer to NATSPEC 0821 Stormwater – Buildings for acoustic treatment of piping.

Refer to NATSPEC 0821 Stormwater – Buildings for Stormwater detention tanks & pumps requirements

Refer to DG/ WATER Section for rainwater reuse considerations.

• Design a drainage on-site detention/retention system (OSD) for the site to requirements of the Local Council.  An above ground OSD or adsorption system is preferred, where practical.
• Design a discharge control pit with an orifice plate and trash screen to be incorporated into the above ground OSD system
• Design a silt arrestor pit to be incorporated into the adsorption system.
• Water level height for OSD basin above ground is a maximum 200mm

GUIDE NOTE: Refer to NATSPEC 0821 Stormwater – Buildings for trenching, bedding & surrounds requirements.

• Connect all subsoil drainage lines to stormwater system.
• Minimum fall of the subsoil drainage system should be 1%
• Provide a Geotextile sleeve to all subsoil drainage lines.
• Where soil conditions are expansive, provide subsoil drains to the high side of flexible pavements.
• Provide subsoil drains to drain boggy ground.
• Provide subsoil draings to all retaining walls above 300mm in height.

Provide:

• Pits at changes of direction of pipe runs carrying ground surface water.
• Ensure that debris cannot enter the stormwater system.
• A pit along straight pipe runs at 100 metres max.
• 225mm-diameter minimum size of outflow pipe from grated pits.
• Scour protection to head walls, pipe outlets and over flows.
• Section of subsoil drainage line to all stormwater pits, on the upstream face, to remove sub-ground moisture from the trenches.
• Flap type or duckbill type reflux valves to stop stormwater back flow into the trenches.
• Litter baskets to carpark and driveway stormwater gullies.
• Where possible, avoid locating in circulation and play areas in order to prevent trip hazards

GUIDE NOTE: Provide dilapidation report prior to the commencement of work.

• Provide suitable methods to maintain existing structures adjacent to new works in a stable condition.
• Provide for safe access to occupied buildings adjacent to new work.

95.11.01 Water Cycle Management Study

The Water Cycle Management Study is to include the following considerations:

• Rainwater reuse
• On Site Retention and Detention
• Erosion Control
• Litter, pollution and sediment control
• Maintenance requirements