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Installation of two CDS hydrodynamic separators.

CDS® Hydrodynamic Separator

The CDS hydrodynamic separator uses swirl concentration and continuous deflective separation to screen, separate and trap trash, debris, sediment, and hydrocarbons from stormwater runoff. CDS captures and retains 100% of floatables and neutrally buoyant debris 4.7 mm or larger, effectively removes sediment, and incorporates a non-blocking screen.
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The CDS Hydrodynamic Separator - Superior Stormwater Trash and Sediment Removal

The CDS is a hydrodynamic separator that uses continuous deflective separation – a combination of swirl concentration and indirect screening to screen, separate and trap debris, sediment, and hydrocarbons from stormwater runoff. The indirect screening capability of the system allows for 100% removal of floatables and neutrally buoyant material debris 4.7mm or larger without binding. CDS retains all captured pollutants, even at high flow rates, and provides easy access for maintenance.

CDS is used to meet trash Total Maximum Daily Load (TMDL) requirements, for stormwater quality control, inlet and outlet pollution control, and as pretreatment for filtration, detention/infiltration, bioretention, rainwater harvesting systems, and Low Impact Development designs.

How the CDS Hydrodynamic Separator Treats Stormwater

  • Stormwater enters the CDS through one or multiple inlets and/or a grate inlet. 
  • The inlet flume guides the treatment flow into the separation chamber where water velocities within the chamber create a swirling vortex.
  • Water velocities in the swirl chamber continually shear debris off the treatment screen.
  • The combination of swirl concentration and indirect screening force floatables and solids to the center of the separation chamber trapping 100% of floatables and neutrally buoyant debris larger than the screen aperture.
  • Sediment settles into an isolated sump while floatables and neutrally buoyant pollutants are captured in the separation cylinder. All pollutants remain in these sections of the unit until they are removed during maintenance.
  • Stormwater then moves under the hydrocarbon baffle, and the treated water exits the system. The baffle acts as a wall for hydrocarbon containment. It contains previously captured hydrocarbons and prevents the agitation of hydrocarbons when high-flows spill over the diversion weir.
  • During high-intensity events, the internal diversion weir directs a portion of flows greater than the design storm around the treatment chamber and over an internal bypass weir.
  • Treated stormwater exits the CDS via the outlet pipe.

CDS Hydrodynamic Separator Features and Benefits

FEATURES BENEFITS
Captures and retains 100% of floatables and neutrally buoyant debris 4.7mm or larger Superior pollutant removal
Self-cleaning screen Ease of maintenance
Isolated storage sump eliminates scour potential Excellent pollutant retention
Internal bypass Eliminates the need for additional structures
Multiple pipe inlets and 90-180º angles Design flexibility
Numerous regulatory approvals Proven performance

The Contech Design Center

The Contech Design Center provides engineers unparalleled flexibility in the layout and configuration of a detention or infiltration storage system. Our latest release includes options previously unavailable in a free, web-based design tool:

  • A 2D/3D design environment with high-resolution graphics, including BIM model output.
  • The ability to import a PDF site plan and design a system to scale over the plan.
  • Provide instant access to customized, project-specific drawings.
  • Design multiple systems per project and save for future use.
  • Digitally collaborate using the new “Project Collaboration” feature. Share your project easily with anyone through the new project management page.
Contech Design Center

Select CDS Certifications

  • Washington Department of Ecology (GULD) - Pretreatment
  • Canadian ISO 14034 Environmental Management – Environmental Technology Verified (ETV)
  • California Statewide Trash Amendments Full Capture System Certified*

State of Washington TAPE GULD Pretreatment

*The CDS System has been certified by the California State Water Resources Control Board as a Full Capture System provided that it is sized to treat the peak flow rate from the region specific 1-year, 1-hour design storm, or the peak flow capacity of the corresponding storm drain, whichever is less.

CDS Configurations

  • Inline, offline, grate inlet, and drop inlet configurations available
  • Internal and external peak bypass options are available

CDS Maintenance

  • CDS provides unobstructed access to stored pollutants, making it easy to maintain.
  • Maintaining a CDS is a simple process that can be easily accomplished using a vacuum truck, with no requirement to enter the unit.
  • Contech has created a network of Certified Maintenance Providers to provide maintenance on stormwater BMP’s.
Installation of a CDS hydrodynamic separator to pretreat a corrugated metal pipe stormwater detention system.
Pretreatment to Storage

Our hydrodynamic separators are frequently installed upstream of detention and infiltration systems as pretreatment devices.  By capturing the majority of sediment, hydrocarbons and trash and debris upstream of the storage system, maintenance becomes much easier as material is congregated into a smaller device with clear access for cleanout.  Additionally, by utilizing pretreatment upstream of infiltration systems, sediment that would have clogged the stone voids in the storage envelope surrounding the storage chamber can be captured before entering the storage system thus extending the longevity of the entire system.

CDS Water Quality unit.
Hydrodynamic Separation for Water Quality

Our hydrodynamic separation products (including the CDS, Cascade Separator, SciCloneX, Vortechs, and Stormceptor Systems) are reliable, easy to install, and offer high-performance, proven, stormwater pollutant removal. The systems are widely accepted for effective solids removal and can be designed to achieve your site treatment goals - including TMDL requirements for TSS and trash.

Trash collected from a CDS hydrodynamic separator.
Trash Removal

Keep trash and debris out of your lakes, streams and oceans by installing one of our technologies at the inlet or outlet of your drainage system.  Our systems - which include the CDS, Cascade Separator, SciCloneX, DSBB, Vortechs, and Stormceptor Systems are most effective on removing sediments, trash and debris, and oil and grease from storm water runoff.

Installation of two CDS hydrodynamic separators.
High Volume Applications

Designing, manufacturing and installing high-volume stormwater detention and treatment systems requires expert engineering, planning, and logistical support to manage costs and keep the project on schedule and under budget. When you need a proven, large scale stormwater management system, “Go Big” with Contech.

Large black drainage pipes installed in a trench at a construction site, surrounded by dirt and barriers.
Pretreatment for Rainwater Harvesting

Our hydrodynamic separation products are ideal solutions for preatreatment to rainwater harvesting.  Not only do they improve the overall water quality, they also provide protect the pumps and controls from being overburdened with material that could clog and damage the mechanical system. 

CDS Solutions Brochure

Hydrodynamic Separator Products Brochure

CDS-vs-Traditional Configuration Flier

Trash Collection Brochure

CDS FAQs

CDS stands for Continuous Deflective Separation. It is a stormwater treatment technology that combines swirl concentration with indirect screening to separate and capture trash, debris, sediment, and hydrocarbons from stormwater runoff.

     An online hydrodynamic separator is installed directly in the storm drain flow path. This allows flows larger than the treatment-design storm to pass through the unit, eliminating the need for a separate bypass structure.

     For more information, please refer to this blog post - Hydrodynamic Separation Devices: Online Vs. Offline 

Vector control in Contech systems is managed through practical design measures that reduce mosquito access while maintaining inspection and maintenance access. Access prevention options include non-vented manhole covers, screened system vents, and mosquito inserts for existing manhole covers. Where standing water or debris may be stored, systems should include inspection and treatment access points. These measures help limit vector access while allowing owners and maintenance providers to inspect, clean, or treat areas of concern without confined-space entry whenever feasible.

CDS units should be visually inspected at least twice per year, with inspections commonly recommended after the spring and fall storm seasons. Cleaning is needed when sediment reaches 75% of the isolated sump capacity or when there is a noticeable accumulation of hydrocarbons, trash, or debris.

Sediment levels can be checked with a calibrated dipstick, tape measure, or similar measuring device. For more information, please refer to the CDS Maintenance Manual. 

Specify CDS when the project requires field-based testing, full trash capture, or trash retention in addition to sediment removal.

If the project is primarily focused on sediment, or TSS, a Cascade Separator may be a good fit depending on local regulations and approval requirements. Contact your local Contech Stormwater Consultant to confirm the best technology for your project.

Proper sizing of a hydrodynamic separator, or HDS system, should begin with a review of applicable local and state stormwater regulations. In many cases, regulations will define the required sizing method and may also identify which products are approved for use.

If there are no specific regulatory requirements, the engineer should first identify the target pollutants, such as trash, sediment, or hydrocarbons, and the required removal performance.

HDS systems are commonly sized using one of two methods: the Point on a Curve method or the Net Annual method. For more detailed information, please refer to our blog posts on these sizing approaches.

Common Sizing Methodologies for Hydrodynamic Separators Part 1: Point on a Curve

Common Sizing Methodologies for Hydrodynamic Separators Part 2: Net Annual Sizing

CDS inlet and outlet pipe sizes vary by unit model, pipe material, and site-specific requirements. Your local Contech Stormwater Consultant can help review the project conditions and confirm the appropriate configuration

CDS units do not require a physical drop from inlet to outlet. In many applications, the inlet and outlet pipes can be set at the same invert elevation.

Hydraulic grade line impacts can vary based on the unit model, flow rate, pipe configuration, and site conditions, so project-specific hydraulic data should be reviewed during design.

Yes, CDS units may be used in tailwater conditions, depending on the tailwater elevation, required treatment rate, hydraulic grade line, and overall site conditions.

Because these factors are project-specific, contact your local Contech Stormwater Consultant to confirm whether CDS is appropriate for your application.

No. The CDS 92 series is only available with a 4,700-micron screen aperture.

Determining where to use a CDS vs a Vortechs is dependent on local regulatory requirements, site conditions, and treatment and bypass flow rates that can impact the size and type of HDS unit.  

CDS is typically the ideal solution for removing and retaining sediment (TSS), trash and debris, and hydrocarbons making it a natural starting point for most preliminary site designs.  

Vortechs offers many of the same benefits as CDS within a shallower and wider footprint.  That shallow footprint makes vortechs a great fit for sites where you may not be able to put a deeper manhole like a CDS.  

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