Thursday, 2 February 2012

Continuous Deflection Separation (CDS)

This week we wanted to find out more about stormwater quality treatment technologies, so we contacted The Shaw Group. They have installed over 150 Continuous Deflection Separation (CDS) systems across the Maritimes. CDS units improve water quality of stormwater runoff by removing sediment, floatables, oil and grease. 

CDS unit (
CDS units have a screen filter that removes all floatable materials and a separate treatment chamber which captures sediment and hydrocarbons. Due to potential high volumes of trapped pollutants, maintenance on these systems is very important. At a minimum they should be maintained twice per year, which includes sucking out the floatable debris and sediment with a vacuum truck.

We went to visit Portland Hills Estates, a large development surrounding Russell Lake, where several CDS units are installed at different stormwater outfalls around the Lake. We saw a ‘56/40 unit’, the largest CDS system which can filter up to 56 cubic feet of water per second.  This system is designed to capture the 1 in 25 year storm (as opposed the 1 in 100 year storm), and as a result it functions very effectively 80% of the time. The other 20% of the time surplus flows through a by-pass valve. 

Let's life the lid and see what is inside!

Wow! Tennis balls, water bottles and several other floatables from the development and neighbouring school are trapped by the CDS. These items would otherwise eventually end up in Russell Lake.
The stormwater outfall is virtually garbage-free!
The impetus for filtering stormwater came from the Russell Lake community group who were concerned about how the Portland Hills Estates development would impact lake water quality. This concern lead to the developer, Clayton Development, including the purchase and installation of these systems into the development agreement. Using these CDS systems is now common practice for Clayton Development.


  1. While an excellent stormwater treatment system, they are only effective when they are cleaned on a regular basis. Unfortunately, the reality is that many owners neglect to clean them. They are often clogged with sediment and rendered inefficient.

  2. You are absolutely right. Without proper maintenance, these systems are ineffective. Shaw recommended cleaning the system a minimum of twice a year, but depending on the location maintenance may be needed more often.
    Please email us with any other filtering systems you know about so we can check them out:

  3. adriancbarker@gmail.com29 February 2016 at 22:33

    This is a non argument - a 'strainer' style filter requires much more maintenance and removal and replacement time than a unit which a single contractor can do with appropriate size lift equipment. The cleaning of the CDS unit can be either done on site or a replacement catchment cage lowered into place while the full one is taken to recyclers or a disposal location for emptying. I doubt that Anonymous has seen the system in operation.

  4. I really like your writing style, great information, thankyou for posting.
    vacuum truck