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CMP Stormwater Detention and Infiltration

CMP Stormwater Detention and Infiltration

Contech’s CMP stormwater detention and infiltration systems store stormwater and release it downstream at an allowable discharge rate or allow it to infiltrate into the surrounding soils. Systems can be sized and shaped to meet site-specific needs, and are available fully or partially perforated.

VoidSaver™ Stormwater Detention System

Stone void contamination is one of the leading threats to the long term reliability of underground stormwater detention systems. Contamination from solids can compromise stone void storage before site stabilization and present a compounding downstream flooding risk each year with long term accumulation.

Industry assumptions of stone voids available for storage are often incorrect in practice. A recent study found 39% of stone backfill samples taken had less than the commonly used 40% void ratio1. Also, construction site sediment runoff often fouls the stone before site stabilization, and one month without proper erosion and sediment management during construction can do more damage than years of sediment accumulation from a paved surface. 

The VoidSaver stormwater detention system alleviates these problems by containing the majority of storm events within the pipe, and only utilizing the stone void storage during infrequent events. As a result, solids are contained within the pipe, and not the stone.


How the VoidSaver Works 

As water fills the gasketed system, trash, debris, and suspended solids settle within the solid pipe rather than filling the stone void space and compromising the system. During large events, water fills the pipe, and the clean water discharges into the surrounding stone via the stone overflow vent. After the storm subsides, water within the pipe continues discharging, creating differential head pressure between the water within the pipe and water within the stone. This external driving head opens the one-way water return valves, allowing the pipe and stone to fully drain down together. 

VoidSaver Features and Benefits




1. Protects stone void space from solids contamination       

1. Protects long term storage capacity and reduces the opportunity for downstream flooding

2. Leverages stone storage to allow smaller system footprints

2. Lower system material and installation costs

3. Does not rely on fabrics for pretreatment to protect surround backfill.

3. No geotextile clogging and more reliable protection of stone voids

4. Provides easier access for maintenance compared to chamber systems.


4. Reduced long-term maintenance costs 


Long Term Reliability

The VoidSaver provides a long-term, reliable solution compared to pretreatment systems that use infiltration methods alongside geotextiles.

By their nature, lower structures such as chambers are naturally more sensitive to occlusion because a high percentage of the designed storage depends on stone voids protected by geotextile. Lab tests of geotextile pretreatment show that geotextiles allow 27-46% of TSS to pass into the voids.1 In addition, clay/silt particles can build up on and clog geotextiles over time requiring extensive and difficult maintenance. This buildup of clay/silt can then make its way over the weirs and into the surrounding backfill compounding the issue over the lifetime of the site. The VoidSaver stores the majority of storm events in the pipe and does not rely on fabrics for pretreatment to protect the surrounding backfill, thus providing a more reliable solution.

VoidSaver Maintenance

Like conventional pipe systems, inspection and maintenance are easily conducted through large access risers where trash and sediment can be removed manually or with a vacuum truck.

1 Cashatt, J.C. (2020), Viability of Stone Void Space in Underground Detention/Retention Systems, Proceedings of EWRI 2020, Henderson, NV, American Society of Civil Engineers

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.


HydroCAD Stormwater Modeling

Contech CMP Detention Systems can be easily modeled with the Hydrocad stormwater modeling system, allowing simplified analysis of the devices' behavior in a drainage and stormwater management system.  The Hydrocad chamber library includes detailed storage data for each Contech product allowing automatic determination of their unique stage-storage characteristics.. Click here for details.

Hydrocad® is a registered trademark of Hydrocad Software Solutions LLC.

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
CMP Stormwater Detention Systems

CMP stormwater detention systems store stormwater runoff exceeding a site’s allowable discharge rate and release it slowly over time. Installed below grade, stormwater detention systems maximize land usage and help meet water quantity requirements.

CMP for Stormwater Infiltration

Perforated CMP infiltration systems store stormwater runoff in the pipe and surrounding stone during a storm until it can be slowly released into the surrounding native soil. Perforated CMP is often used to meet Low Impact Development requirements.

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.

Low profile/Low drop

Small diameter or pipe-arch shaped CMP can maximize vertical storage space. The low, wide pipe-arch design allows for greater storage in a shallow profile than typical round pipe without losing any structural integrity.

Bioretention and Subsurface Infiltration with Perforated CMP

Perforated CMP stores stormwater runoff exceeding a site’s allowable discharge rate and releases it slowly over time. Various coatings are available to achieve 75-100 year design service life. Rectangular, L-shaped, and staggered cells are frequently used to design around existing utilities.

Technical information for this product is centrally located in the technical guides section.

View Technical Information

CMP Detention and Infiltration - Meet Stormwater Quantity and Runoff Reduction Requirements

Corrugated metal pipe (CMP) is the “go to” material for the majority of detention and infiltration projects. Contech’s CMP detention and infiltration systems and can be sized and shaped to meet site-specific needs. 

  • NCSPA service life guidance of 75+ years for certain materials in recommended environments. Please refer to the Corrugated Metal Pipe Detention Design Guide for additional information.
  • Various pipe coatings and materials are available to accommodate site-specific needs: Aluminized Steel Type 2 (ALT2), Galvanized, CORLIX® Aluminum, and Polymeric.
  • Wide range of gages, corrugations, and shapes, in diameters 12” – 144”.
  • Pipe can be fully or partially perforated for infiltration or groundwater recharge applications.
  • Custom access risers and manifolds provide direct access for maintenance.
  • Outlet control devices can be incorporated within the system, eliminating the need for a separate structure.
  • Customizable - a variety of fittings allow CMP to match most layout configurations.
  • May be designed for heavy loading and high maximum cover.
  • Contributes to LEED points.
  • Available locally; quick turnaround time.
  • The most economical installed solution.

The Contech Advantage

Agency/Regulatory Guidance

Our team is ready to provide you with expert advice and assistance on local regulatory requirements, resulting in faster approvals.

Solution Development

Our engineers can review your requirements, weigh all options, and recommend the optimal solution to integrate with your site designs.

Technical Expertise

Our engineers can assist by providing product specific engineering calculations such as hydraulics, buoyancy, foundation reactions, and unit sizing.

Cost Estimates

We can quickly provide engineer’s cost
estimates to assist with your solution
selection process.

Site Specific Drawings

Our engineers can provide site-specific drawings for proposals, project meetings, and submittals, helping you be more efficient with your time.

On-site Assistance

Contractors know time is money, so we provide preconstruction meetings, delivery coordination, and on-site installation support to ensure a timely, smooth installation.