The Downstream Defender® has unique flow modifying components that have been optimised to deliver unsurpassed capture and retention of pollutants during both frequent and extreme rainfall events. 

The Downstream Defender® delivers high removal of pollutants through advanced hydrodynamic vortex separation across a wide range of flows, achieving a long, stable flow path to maximise pollutant capture from surface runoff.   

The device is able to tackle an assortment of pollutants including gross debris, litter, hydrocarbons, coarse sediments, fine sediments and particulate organics. In the field, pollution captured by the Downstream Defender® has been shown to be as fine as the pollutants captured in much larger settling ponds.

Targeted Pollutants
		Fine particles
		Gross pollutants
		Liquid and sediment bound hydrocarbons
		Sediment bound heavy metals
		Sediment bound nutrients

Applications

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

It is also widely used to control siltation upstream of wetlands, ponds and basins, for example as an alternative to a sediment forebay, and can help to reduce the maintenance burden of natural SuDS features.

No Risk of Pollutant Wash Out

The Downstream Defender® has proven ability to prevent washout of captured pollutants.  Carefully designed internal components isolate the pollution storage areas ensuring what is captured is retained, even during, even during peak storm events.

Easy to Install and Maintain

The Downstream Defender® is delivered to site as a pre-cast concrete manhole chamber with internal components already installed.  Installation is therefore similar to any other manhole.

Maintenance is significantly easier than for diffuse solutions (such as swales or trenches) or large management structures (such as ponds or wetlands) by offering long maintenance intervals also consolidating activity to a single point within the drainage system.  Maintenance of the device is carried out from the surface using a standard vacuum tanker and personnel are not required to enter the device.

Adaptable

The Downstream Defender® can accommodate a change in outlet pipe direction to suit site specific requirements, meeting Building Regulation requirements without the need to construct a second manhole.  

A Proven Track Record

Hydro International’s Downstream Defender® has a proven track record with regulatory agencies around the world, including:

• US Environmental Protection Agency’s Environmental Technology Verification
• Massachusetts Stormwater Technology Evaluation Project (MASSTEP)
• State of Washington Department of Ecology
• New Jersey Department of Environmental Protection
• Wisconsin Department of Commerce
• Ontario Ministry of the Environment
• The City of Calgary
• New York State Department of Transportation

Treatment Processes

•  Enhanced sedimentation.

•  Flotation.

Operation

The Downstream Defender® internal components are designed to enhance the separation process by minimising turbulence and head loss, increasing efficiency and preventing wash out of captured pollutants.

Contaminated surface water runoff entering the chamber is directed downwards and around the periphery of the chamber.

Oils, litter and other floatable material is initially captured at the inlet and transferred to the oil storage zone as flows increase.  The oil storage zone is protected from the treatment flow path and so prevents captured floatable material from wash out during peak flow­s.

As the flow continues to spiral around the periphery of the chamber, low energy vortex motion directs settleable solids into the base of the unit.  The internal components isolate the base of the chamber from the treatment flow path preventing wash out of captured solids.

The treated water exits the chamber via the orientated outlet pipe after ensuring the longest possible retention time within the unit.

Excess flows by-pass the vortex treatment chamber and also both the sediment and oil storage zones.  These excess flows pass forward untreated via the orientated outlet pipe.

Frequently Asked Questions

Q. When do I use a First Defense® for surface water treatment instead of a Downstream Defender®?

When the treatment flow of a site is small, the First Defense® may be a more suitable treatment device. The First Defense® may also be a more suitable alternative when the influent will be entering the device via a storm grate on the surface. Try our Surface Water Treatment Selection Tool to help you decide on an appropriate treatment package for your given application or contact our Design Support Team on 01275 337955.

Q. What sizes are available? Which size should I use?

The Downstream Defender® is available as a 1.2 m, 1.8 m, 2.55 m and 3.0 m diameter unit.  The unit size needed for your application depends upon a number of factors including the level of treatment desired, the target pollutant, the water quality flow rate and the peak drainage system flow rate. Contact our Design Support Team on 01275 337955 for technical assistance.

Q. What size inlet/outlet pipe is acceptable?

The 1.2 m diameter unit accepts connection of 300 mm ID inlet and outlet pipes.

The 1.8 m diameter unit accepts connection of 450 mm ID inlet and outlet pipes.

The 2.55 m diameter unit accepts connection of 600 mm ID inlet and outlet pipes.

The 3.0 m diameter unit accepts connection of 750 mm ID inlet and outlet pipes.

Q. Can the Downstream Defender accept two inlet pipes?

No, the internal components are designed to enhance the separation process and isolate the pollutant storage zones.

The angle of the outlet pipe is variable through a 180 degree arc (from 90 degrees to 270 degrees to the inlet pipe).  2-3 m of straight pipe should be connected to either side of the Downstream Defender® unit before any further changes in angle or pipe dimension are made.

Q. Can the units be modified from the specifications shown in the brochure?

No. The internal components within the Downstream Defender® unit act to enhance the separation process and to isolate the captured pollutants from the treatment flow path in order to prevent wash out.  As the separation process is driven entirely by the hydraulic processes within the unit, the Downstream Defender® relies on certain critical dimensions and fixed pipe sizes in order to function correctly and these cannot be modified.

The angle of the outlet pipe is variable through a 180 degree arc (from 90 degrees to 270 degrees to the inlet pipe).  2-3 m of straight pipe should be connected to either side of the Downstream Defender® unit before any further changes in angle or pipe dimension are made.

Q. What is the maintenance procedure?  Is confined space entry required?  How often is maintenance needed?

Watch our maintenance video to see how easy the Downstream Defender® maintenance is.

Maintenance is safe and easy and can be carried out from the surface using a standard vacuum tanker.  No man entry is required.  Maintenance consists of removing sediments from the sump and floatable oils, grease, litter and other debris from the floatables capture zone.

The maintenance interval will depend on the type of catchment, the water quality and peak flow rates and the pollutant load seen by the device.  Contact our Design Support Team on 01275 337955 for an estimation of maintenance intervals for your site.

Q. What is removal efficiency of the different size units?

Removal efficiency is dependent upon the particle size and specific gravity of the pollutant, in addition to the water quality and peak flow rate of the runoff.  Contact our Design Support Team on 01275 337955 for technical advice.

Q. Does installation of the Downstream Defender® require any special equipment or experience?

The installation process of a Downstream Defender® is similar to installing a standard manhole as all the internal components are supplied ready fitted into the chamber.  Full installation guidelines can be obtained from our Design Support Team on 01275 337955.

Q. Is the Downstream Defender® an equivalent to an oil interceptor?

The Downstream Defender® has been independently tested and found to meet the removal requirements for a Class II oil interceptor under certain flow conditions.  However, oil interceptors are only designed to tackle liquid hydrocarbons.  Various research studies have shown that up to 98% of hydrocarbon pollution in urban waters is attached to sediment particles.  As the Downstream Defender® is specifically designed to remove sediment, it will also remove the attached hydrocarbons.