The benefits of engineered solutions for treating road and highway runoff
Manufactured or engineered devices for treating surface water runoff from highways can provide designers and maintenance operatives with cost-effective, efficient and reliable stormwater treatment.
Hydro International are experts in removing solids from liquids using hydrodynamic vortex separation, and have over 40 years’ experience in doing this for stormwater, wastewater and combined sewer flows.
The first advanced hydrodynamic vortex separator that National Highways (then the Highways Agency) tested for highway runoff was the Downstream Defender®, where units were installed along a stretch of the M25.
Following this testing, advanced vortex separators were then deemed to be suitable for removing pollutants from highway and road runoff and were included in the Design Manual for Roads and Bridges (CD528).
Since then, we have continued to test and develop our separators, and in 2022 launched our latest generation of advanced hydrodynamic vortex separator for stormwater treatment – the Downstream Defender® Select.
Designed specifically for treating runoff from highways and roads in urban areas, the Downstream Defender® Select is our most flexible and customisable separator to date.
With three models to choose from, a wide range of chamber sizes, and options for improved retention, design engineers can select which level of performance they need, depending on the application. This customisable performance makes it ideal in meeting treatment objectives such as the CIRIA SuDS Manual’s Simple Index Approach (C753)
With over 200 units for over 50 road or highway projects across the UK, Hydro International’s advanced vortex separators have a proven track record and our most popular option for preventing pollution from surface water runoff.
Using the energy inherent in the flow, the Downstream Defender® Select removes and retains a variety of pollutants including:
The floatable pollutants are stored in a zone at the top of the unit and settleable sediments are stored in the sump, away from the active separation zone.
With options for enhanced sediment and hydrocarbon retention, Downstream Defender® Select keeps what it captures – for up to four times the design flow rate without washout!
Up until recently there were no UK test protocols for proprietary systems, so US or Europe protocols, such as the New Jersey Department for Environment Protection (NJDEP) or the Deutsches Institut für Bautechnik (DIBt) were followed.
In 2016 British Water launched a code of practice the “Assessment of Manufactured Treatment Devices Designed to Treat Surface Water Runoff”, the first such testing protocol in the UK. Its robust testing approach enables verification of the capture and retention capabilities of proprietary devices for a range of pollutants and enables designers and local authorities to select the best device for a given application.
The Downstream Defender® Select has been tested in accordance with the British Water code of practice, and the two higher performing models, the Vortex Plus and Advanced Vortex have also been verified by the WRc. Data from the testing and the WRc declaration can be found on the British Water website.
Alternative sizing methods, especially those based on coarse sediments or a set particle size (eg. OK110 test sediment) may not represent accurate storm conditions and may result in undersized units. At high flow rates a unit which is too small may not remove/ retain typical pollutants found in urban runoff. This will potentially cause carry over and allow contamination to pass further downstream meaning highly polluted silts and sediments could eventually end up in watercourses. Engineers that are looking for reliable, repeatable performance data should not rely on alternative sizing methods such as these.
Try out your own designs
Free online design tool
Have a go at customising your own Downstream Defender® Select with the free online design tool.
Log in or register for the online tool at: hydro-int.design
Tight spaces and retrofit
With its compact design and small footprint, the Downstream Defender® Select can be fitted into existing drainage lines in the highway boundary. This also makes it ideal for retrofitting.
Installation
For quicker, safer installation, the Downstream Defender® Select is delivered pre-installed inside a concrete chamber so that, once positioned, it can be directly connected to pipework.
Supplied as standard in a concrete chamber, for sites where access for heavy plant may be restricted or where fast installation is required the Downstream Defender® Select can also be supplied in a plastic chamber.
Single or reduced points for maintenance can save time at the roadside, reducing the risk for maintenance teams.
Using a Downstream Defender® Select can also reduce frequency of maintenance for other drainage components.
For instance, if discharging into a detention basin or a pond, siting a Downstream Defender® Select upstream can ensure that the storage capacity isn’t compromised by the deposition of silts and can also help preserve the biodiversity of a pond by removing oils, sediments and their associated pollutants from the flow.
A Hydro-Logic® Smart Maintenance package can be added to the Downstream Defender® Select which will deliver automated maintenance alerts, helping to ensure that maintenance is carried out in a targeted way, and only when required. This can help with maintenance planning and also lessen risk and costs by reducing the need for regular inspection visits for units installed alongside the highway.
The package can also be retrofitted into existing Downstream Defender® separators.
Case study - Richmond Park
As part of Beverley Brook Catchment Partnership plans to improve the status of the Beverley Brook, in Richmond Park, London, a range of restoration and mitigation measures have been carried out in the park by the South East Rivers Trust (SERT) over several years.
As part of this project a Downstream Defender® is removing pollutants from urban road runoff to help protect the Beverley Brook, capturing circa 7 m3 per year of contaminated sediment. It’s the first unit to have the Hydro-Logic® Smart Maintenance package installed and can be monitored remotely and sends alerts when it needs emptying.
Watch the video about Richmond Park
We're happy to help with design and sizing
If you'd like assistance with a project, please get in touch
Book a CPD training session on Sustainable Drainage for Highways
Find out about our range of stormwater treatment solutions for highway runoff and how our flow control solutions can help you control flows and prevent flooding. Book a training presentation for you and your colleagues.
