Attenuation can bring about a reduction in the force of stormwater by carefully controlling the level of flow. Attenuation involves holding back large amounts of rainwater in a geocellular crate system and allowing the discharge rate to be controlled by a flow control at a discharge control point. 

Temporary storage and discharge – holding stormwater in cellular storage crates and then a reduction in the force exiting the structure by controlling the flow of water with a flow control unit. The slow-rate of discharge enables local authorities to avoid downstream flooding and the erosion of waterways due to heavy flows. 

In this application, Rainsmart geocellular crates are used with an impermeable membrane and relevant flow control in order to achieve attenuation. 

Step by Step Attenuation

  • Stage 1 - Stormwater flows into a silt trap (or catchpit) to catch debris, improve water quality & prevent blockages further in the system
  • Stage 2 - The filtered stormwater enters the pre-built geocellular crate system at a size that will hold the required level of stormwater
  • Stage 3 - Stormwater is held in the tank which is wrapped in an impermeable membrane liner - this can be purchased by the roll or as a pre-built shoebox.
  • Stage 4 - A flow control chamber then manages the discharge rate of stormwater into the main surface water drainage network.