The Downstream Defender® is an advanced hydrodynamic vortex 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 stand-alone device, providing engineers and contractors with a flexible, cost-effective stormwater management option.  

Targeted Pollutants:

  • Fine and coarse particles / total suspended solids (TSS)
  • Floatable trash and debris
  • Liquid- and sediment-bound oils and hydrocarbons
  • Sediment-bound heavy metals
  • Sediment-bound nutrients


The Downstream Defender® reliably treats surface water runoff from impermeable surfaces including highways, car parks, industrial areas and urban developments

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

Certifications & Verifications: 

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 requires less work.

The Downstream Defender® is proven to prevent washout of captured pollutants. Carefully designed internal components isolate the pollution storage areas, ensuring that 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 engineers with design options for shallower sites.

How it works

How it works

The Downstream Defender® stormwater treatment system is 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

Technical information

Unit sizes (diameter)

  • 4 ft / 1.2 m
  • 6 ft / 1.8 m
  • 8 ft / 2.4 m
  • 10 ft / 3.0 m
  • 12 ft / 3.7 m

Performance characteristics          

  • Hydraulic capacity: 3.0 - 38 cfs
  • Oil storage capacity:  70 - 1,770 gal
  • Sediment storage capacity: 0.7 - 14.7 cu yd

Technical Specifications Downstream Defender

*12-ft units are not available in all areas. Please contact us for further information. 



Case Studies

Case Studies