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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.
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:
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.
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.
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.
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.
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.
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.
Yes. The riser does not need to match the diameter of the main pipe. In fact, risers are typically smaller than the main barrel to help maintain a structurally sound fabricated tee connection. Standard risers are usually 30" or 36", though other sizes may be used depending on access, hydraulic, and outlet control needs.
Yes. CMP detention systems can be used on modest, uniform slopes, typically where finished grades are 10% or less. Proper design depends on the pipe diameter, height of cover, and slope geometry. Steep cross slopes should be avoided because uneven cover can create unbalanced soil loads that may affect structural performance.
Separation requirements vary by system type and jurisdiction. For solid, watertight systems, there is generally no prescribed minimum or maximum separation, but potential submergence should be evaluated through a buoyancy analysis. For perforated infiltration or xFiltration systems, local regulations typically require 2 to 4 feet of separation between the system invert and the seasonal high water table. Project-specific requirements should always be confirmed with the local stormwater authority.
Yes. Stage-storage tables are a standard deliverable, generated either by the Contech design team or by the specifying engineer using the Contech Design Center.
Yes. CMP detention systems can often be designed with curved layouts using fabricated bends or by laying pipe on a curve. The achievable radius depends on factors such as pipe diameter, wall thickness, joint configuration, and site layout. The Contech team can provide project-specific guidance on available fitting options and layout requirements.
Buoyant forces should be considered whenever the seasonal high groundwater elevation is at or above the pipe invert. A buoyancy check should compare potential uplift against the resisting weight of the system, backfill, cover, and pavement, using an appropriate safety factor. If needed, mitigation may include raising the invert, adding cover, or using anti-flotation measures such as tie-downs to concrete deadmen.
No. CMP detention systems can accommodate inlets and outlets of various pipe materials. Dissimilar-material couplers or shop-fabricated transitions can be used at the connections as needed.
No. A full geotextile wrap is not typically required. Geotextile fabric may be used selectively where needed to prevent fines migration or separate dissimilar backfill materials.
Vector control is typically managed through a combination of exclusion and treatment access. Exclusion measures may include non-vented manhole covers, screened vents, and mosquito inserts to help prevent adult mosquitoes from entering the system. Where treatment access is needed, CMP detention systems can include inspection points, typically with a minimum 6-inch access opening, to allow larvicide products such as liquids, briquettes, granules, or dunks to be applied without requiring confined-space entry
No. Vertically stacked CMP detention systems are not recommended due to structural loading and safety concerns. If additional storage volume is required, the system should typically be designed using larger-diameter pipe or an expanded footprint rather than a stacked configuration.
Corrugated metal pipe (CMP) is often the most economical choice for deep-burial underground stormwater detention systems. Maximum cover depth varies depending on the pipe diameter and gauge. For tailored recommendations based on your project site and loading conditions, we encourage you to consult a Contech representative.
Yes. CMP detention systems can be designed for heavy-load applications when the appropriate pipe gage, cover depth, and backfill are used. These applications should be evaluated as engineered loading conditions, and Contech can provide design guidance for many common heavy-load scenarios.
Special consideration is required for cranes and other equipment that can create concentrated point loads. Cranes should not be positioned directly over the pipe without a project-specific load evaluation and appropriate load-distribution measures.
CMP detention systems are generally designed to be soil-tight or leak-resistant rather than fully watertight. Contech offers several jointing options to provide a tighter connection than standard bands when greater control of leakage is required.
For applications requiring a higher level of watertight performance, DuroMaxx is also available with several joint configurations, including a welded coupler (WC), 10.8 psi high-performance (HP) bell-and-spigot joint, and soil-tight (ST) joints. The appropriate pipe material and joint system should be selected based on the project’s specific performance requirements.
Proper installation helps ensure long-term system performance. Key considerations include:
Contech provides installation and construction-loading guidance to help contractors follow recommended practices in the field.
It depends on the available burial depth, required storage volume, and site conditions. When adequate depth is available, larger-diameter CMP can provide significant storage volume very efficiently. Because pipe storage capacity increases substantially as diameter increases, CMP can be especially cost-effective on sites where deeper burial is practical.
Plastic chambers may be better suited to sites with shallow cover requirements, limited excavation depth, or high groundwater conditions. The most cost-effective solution should be evaluated based on the specific site and project requirements.
Recommended spacing between adjacent CMP barrels generally varies by pipe diameter:
Proper barrel spacing provides room for backfill placement and compaction and helps support the structural performance of the system. Project-specific conditions should also be considered during design.
No. Contech CMP detention systems do not require washout twice per year as a standard maintenance practice.
Contech recommends inspecting the system at least annually. Inspection frequency may need to increase in areas where higher sediment, debris, or corrosive conditions are expected, such as equipment washdown areas or locations that use road sand and deicing salts.
Cleaning should be performed as needed based on inspection findings, particularly if accumulated sediment or debris begins to restrict the outlet orifice. Sediment and debris can typically be removed through the access manhole near the outlet.
For additional guidance, refer to the CMP Detention & Infiltration Maintenance Guide.
Inlet stubs are typically located near the top of the system to maximize available storage volume.
For detention systems, outlet stubs are generally located near the system invert to allow the system to drain fully.
For retention systems, outlet stubs typically function as overflow connections and are generally located at or just below the inlet stub elevation.
Our team is ready to provide you with expert advice and assistance on local regulatory requirements, resulting in faster approvals.
Our engineers can review your requirements, weigh all options, and recommend the optimal solution to integrate with your site designs.
Our engineers can assist by providing product specific engineering calculations such as hydraulics, buoyancy, foundation reactions, and unit sizing.
We can quickly provide engineer’s cost
estimates to assist with your solution
selection process.
Our engineers can provide site-specific drawings for proposals, project meetings, and submittals, helping you be more efficient with your time.
Contractors know time is money, so we provide preconstruction meetings, delivery coordination, and on-site installation support to ensure a timely, smooth installation.
