The Downstream Defender® is an advanced hydrodynamic separator that provides impressive and reliable removal of fine and coarse particles, hydrocarbons and floatable debris from surface water runoff, delivering high levels of stormwater treatment over a wide range of flow rates. 

Available in a range of sizes, it can function as either pretreatment or as a standalone device.  

Targeted Pollutants:

  • Fine particles
  • Floatable debris
  • Liquid and sediment bound hydrocarbons
  • Sediment bound heavy metals
  • Sediment bound nutrients


The Downstream Defender® reliably treats runoff from impermeable surfaces including highways, car parks and industrial areas.

  • As part of LID or LEED systems
  • Areas where high solids and trash capture are a must
  • Control of silting upstream of wetlands, ponds and basins


Designed for

Coarse particles

High flow

Oils & hydrocarbons

Trash & floatables


Save space and money

Downstream Defender® can treat high peak flows in as little as half of the footprint of other structural BMP systems. A smaller footprint means an easier install that's less expensive and less work.

The Downstream Defender® is proven to prevent wash out of captured pollutants. Carefully designed internal components isolate the pollution storage areas ensuring what is captured is retained, even during high flows.


The Downstream Defender® can accommodate a change in outlet pipe direction to suit site specific requirements. 

Cut headloss

Low headloss means more site flexibility and provides the option for a shallower site. 


How it works

The Downstream Defender® has internal components designed to enhance vortex separation by minimizing turbulence and headloss, increasing efficiency, and preventing washout of stored pollutants. 

1. Contaminated stormwater is introduced tangentially into the side of the vessel, generating a rotating flow that spirals around the outside of the dip plate.

2. Oils, trash and floatable debris rise to the water surface and are trapped in the oil and floatables storage volume.

3. As flow continues to spiral down around the dip plate cylinder, low energy vortex motion directs sediment inward along the benching skirt and into the protected sediment storage zone.

4. The benching skirt and center cone redirect the rotating flow up and inward between the center shaft and dip plate cylinder away from the stored sediment.

5. The outlet pipe discharges treated effluent from within the dip plate cylinder ensuring the longest possible residence time. 



Technical information

Unit sizes (diameter)

  • 4 ft
  • 6 ft
  • 8 ft
  • 10 ft
  • 12 ft

Performance characteristics          

Hydraulic capacity: 3.0 - 38 cfs

Oil storage capacity:  70-1770 gal

Technical Specifications Downstream Defender

*12-ft units not available in all areas.