United States Department of Agriculture 656-CPS-1

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NRCS reviews and periodically updates conservation practice standards. To obtain the current 

version of this standard, contact your Natural Resources Conservation Service State office or 

visit the Field Office Technical Guide online by going to the NRCS website at 

https://www.nrcs.usda.gov/ and type FOTG in the search field. 

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Natural Resources Conservation Service 

CONSERVATION PRACTICE STANDARD 

CONSTRUCTED WETLAND 

CODE 656 

(ac)

DEFINITION 

An artificial wetland ecosystem with hydrophytic vegetation for biological treatment of water. 

PURPOSE 

Use this practice to accomplish one or more of the following purposes: 

• Treat wastewater or contaminated runoff from agricultural processing, livestock, or aquaculture

facilities. 

• Improve water quality of storm water runoff, tile drainage outflow, or other waterflows. 

CONDITIONS WHERE PRACTICE APPLIES 

This standard applies where at least one of the following conditions occurs: 

• Wastewater treatment is necessary for organic wastes generated by agricultural production or

processing. 

• Water quality improvement is necessary for agricultural storm water runoff, existing tile drainage

outflow, greenhouse wastewater, or other waterflows. 

A constructed wetland is applied where wetland function can be created to provide treatment of

wastewater or other agricultural waterflows. 

Do not use this standard in lieu of NRCS Conservation Practice Standards (CPS) Wetland Restoration

(Code 657), Wetland Creation (Code 658), or Wetland Enhancement (Code 659), for which the main

purpose is to restore, create, or enhance wetland functions other than wastewater treatment or water

quality improvement. 

CRITERIA 

General Criteria Applicable to All Purposes 

Plan, design, and install constructed wetlands to comply with Federal, State, and local laws and

regulations. 

Locate the constructed wetland to minimize the potential for contamination of ground water resources and

protect aesthetic values. 

Determine the design parameters, such as surface area and length-to-width ratio, to provide hydraulic

retention time necessary for treatment using NRCS National Engineering Handbook (NEH) (Title 210),

Part 637, Chapter 3, “Constructed Wetlands,” or alternative design procedures recognized by the

regulatory and academic conservation partners in the State. 
Provide appropriate inlet control structures to prevent debris from entering the wetland, to control the rate

of inflow during normal operations, and to control inflow as necessary for operation and maintenance. 

Provide an outlet control structure capable of maintaining appropriate water depths to achieve the desired

water treatment and meet the requirements of the hydrophytic vegetation. Refer to NRCS CPS Structure

for Water Control (Code 587) for design criteria. 

Design the minimum height of interior embankments to contain the design water depth and a sufficient

depth for the accretion of settleable solids, decayed plant litter, and microbial biomass. In the absence of

an accretion rate analysis, design the minimum depth for accretion of 1 inch per year for the design life of

the practice or between scheduled debris and sediment removal maintenance operations. 

Provide the impoundment with sufficient capacity to handle the peak flow and runoff volume from the 25-

year frequency, 24-hour duration storm without overtopping the embankment, and provide erosion

protection for the perimeter embankment. Capacity may be achieved through the outlet control structure,

temporary storage, or an auxiliary spillway. 

Unless otherwise specified, refer to the design criteria contained in NRCS CPS Pond (Code 378) for the

spillway requirements, embankment configurations, excavated side slopes, embankment soils, protective

cover on disturbed soils, and disposal of excavated material. 

Use a planting medium with a cation exchange capacity, pH, electrical conductivity, organic matter, and

textural class conducive to wetland plant growth and retention of contaminants. 

For a constructed wetland where specific wetland vegetation is to be planted, select wetland species

suitable for local climatic conditions and tolerant of the concentrations of nutrients, pesticides, salts, and

other contaminants flowing into the wetland. Do not use invasive or other noxious species that could

spread and become a nuisance to surrounding wetlands. Refer to the USDA PLANTS Database and

appropriate State technical information for recommended species and seeding methods. 

Provide supplemental water as necessary to establish and maintain plants in a condition suitable for the

water treatment purpose. 

Exclude livestock from the constructed wetland to prevent damage to the plants, embankments, and water

control structures. 

Safety.—When used in populated areas, install safety fences and warning signs forbidding access by

unauthorized persons. 

Provide adequate access for cleanout and maintenance. 

Additional Criteria for Constructed Wetlands for Waste Treatment 

Locate the constructed wetland outside the boundary area of natural wetlands of any classification. 

Locate a constructed wetland for wastewater treatment above the 25-year floodplain elevation unless site

restrictions require location within the floodplain. When located in a floodplain, provide protection from

inundation or damage from a 25-year frequency, 24-hour flood event. 

Pretreat water flowing to the wetland to reduce the concentrations of solids, organics, and nutrients to

levels the wetland system will tolerate and to prevent excessive accumulation of solids within the wetland. 

Divert runoff from above or provide sufficient storage upstream of the wetland to contain the wastewater to

be treated and the precipitation/runoff from a 25-year frequency, 24-hour duration storm. Design the outlet

of this storage to deliver water to the wetland at a rate consistent with the treatment objectives of the

wetland. 

Design the wetland system with a minimum of two rows of functionally parallel cells. 

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Seepage control 

Where appropriate, design seepage control measures according to the procedures in 210-NEH, Part 651,

Chapter 10, Appendix 10D, “Design and Construction Guidelines for Waste Impoundments Lined with

Clay or Amendment-treated Soil.” 

Additional Criteria for Constructed Wetlands for Water Quality Improvement 

When located in a floodplain or watercourse, provide protection from damage from a minimum 10-year

frequency, 24-hour flood event. 

When used to improve the quality of surface water runoff, design the wetland so that water levels will

return to design operating levels within 72 hours after a 10-year frequency, 24-hour duration storm event. 

Use design procedures recognized by the regulatory and academic conservation partners in the State.

Select a design hydraulic retention time that will achieve the intended water quality results. 

CONSIDERATIONS 

General Considerations 

Source Water Protection 

Consider providing an increased level of designed treatment for sites with high priority areas for source

water protection or are upstream of community drinking water withdrawal sites. Drinking water sources

need protection from nutrients, sediments, pathogens, and pesticides as well as harmful algal blooms

which can result from excess nutrients. Providing an increased level of safety factor can help protect these

community water systems. 

Landscape impact 

Consider the impact a constructed wetland could have on existing wetlands or potentially affected wetland

easements, as well as potential impacts on watershed or other significant features in the landscape

ecosystem. Consider selecting plants that occur within the documented range and are adapted to the

specific site conditions. See the USDA PLANTS Database. 

When constructed in or near populated areas, consider the potential of odor in regard to prevailing winds. 

Vector and nuisance insect control 

Consider installing bat boxes, mosquito fish, and other measures to control vectors and nuisance insects

when locating the wetland near residences, commercial buildings, and public use areas. 

Seasonal storage of contaminated water 

Consider seasonal storage of contaminated water upstream of the wetland during cold, dry, or excessively

wet climatic conditions when the intended wetland function may be compromised. 

Recycling effluent 

Consider storing constructed wetland effluent for land application, recycling through the wastewater

management system, or using elsewhere in the agricultural operation. 

Wetland performance 

Consider providing a structure that captures the first flush of storm water runoff and allows excess flow to

bypass the wetland in situations where wetland performance may be compromised by large, infrequent

storm events. 

Consider installing a sediment basin and reaches of shallow and deep water within the wetland to

enhance wetland function. 

Provide inflow and outflow structures and cell geometries that promote cross-sectional mixing of water

flowing through the wetland cell. 

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Consider the potential of pollutants entering the wetland that may cause environmental problems due to

accumulation, biological uptake, or release during maintenance operations. 

Consider vegetative buffers around the perimeter of the constructed wetland to protect from buildup of

sediment. Adding buffer is an economic decision for the producer since adding buffer will reduce the

maintenance need to remove sediment but potentially takes land out of production. 

Plant materials 

When selecting vegetative species, give priority to native wetland plants collected or grown from material

within the major land resource area (MLRA) of the constructed wetland location, and consider the

potential to transport chemical contamination from the wetland plant site to the constructed wetland. 

Select plant materials that provide habitat requirements for desirable wildlife and pollinators. The addition

of native forbs and legumes to grass mixes will increase the value of plantings for both wildlife and

pollinators. 

Access 

Use fences or other measures as needed to exclude or minimize access of humans or animals that could

adversely affect the constructed wetland or inhibit its function. 

Consider access for animals attracted to the wetland and egress for fish that could be entrained and

trapped. Flatter side slopes generally provide better habitat for wildlife. If there is a desire to use the

constructed wetland for wildlife habitat as a secondary benefit, consult NRCS CPS Wetland Restoration

(Code 657), Wetland Creation (Code 658), Wetland Enhancement (Code 659), Wetland Wildlife Habitat

Management (Code 644), and Shallow Water Development and Management (Code 646) for appropriate

design elements. 

Embankment protection 

Consider providing embankment protection against burrowing animals. 

Climate change 

The accretion of organic sediments in constructed wetlands represents sequestered carbon. Consider

methods and timing of operation and maintenance steps to remove accumulated organic matter that will

limit oxidation of the accumulated solids, such as spreading and incorporating the organic matter as

quickly as possible. Additionally, consider if steps need to be taken to account for impacts in the region

due to climate change, including stressors, such as extreme precipitation events, increased heavy

downpours, and resulting increase in mobilization of pollutants (sediment and nutrients), or the need for

drought tolerance. 

PLANS AND SPECIFICATIONS 

Prepare plans and specifications for constructed wetlands that describe the requirements for applying the

practice according to this standard. As a minimum, the plans and specifications must include, but are not

limited to, the following items:. 

• A site-specific plan view of the practice showing the main features of the constructed wetland in

relation to each other and the waste management system, if applicable. 

• Specifications or information documented as construction notes on the construction drawings that

include materials, methods, and sequence. 

• Location, size, type of material, and elevations of all structures. 

• Typical cross sections of the constructed wetland, including berm dimensions and side slopes, if

applicable. 

• Plant species selection. 

• Rates for seeding, sprigging, or planting density for containerized plants. 

• Planting dates, care, and handling of the seed or plant materials to ensure that planted materials

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have an acceptable rate of survival. 

• Site preparation such as stabilizing crop, mulching, or mechanical means of stabilizing, fertilizer,

and pH adjustment sufficient to establish and grow selected plant species. 

OPERATION AND MAINTENANCE 

Develop an operation and maintenance plan and review the plan with the operator responsible for the

success of this practice. 

Include the requirements for safety, water management, cleanout of sediment and accumulated organic

matter, maintenance of structures, embankments, and vegetation, control measures for vectors and pests,

and containment of potential pollutants during maintenance operations. 

Operational requirements include, as appropriate, but not limited to, the following items: 

• Maintenance of water level in wetland cells appropriate for vegetation. 

• Control flow to wetland according to water budget. 

• Monitoring of wetland performance. 

• Sampling effluent for nutrients prior to utilization. 

• Inspection of inlet and outlet structures for damage after large storm events and at least annually. 

Maintenance requirements include, as appropriate, but not limited to, the following items: 

• Repair of embankments. 

• Control density of desirable vegetation. 

• Removal of invasive and/or non-native species that could be a problem in native habitats. 

• Debris and sediment removal. 

• Repair of fences or other ancillary features. 

• Replacement of wetland plants. 

• Repair of pipelines and spillways. 

• Control of unwanted rodents or vectors (mosquitoes). 

REFERENCES 

Boets, P., E. Michels, E. Meers, and K. Lock. 2011. Integrated Constructed Wetlands (ICW): Ecological

Development in Constructed Wetlands for Manure Treatment. Wetlands 31:763-771. 

Smith, E., R. Gordon, A. Madani, and G. Stratton. 2006. Year-Round Treatment of Dairy Wastewater by

Constructed Wetlands in Atlantic Canada. Wetlands 26:349-357. 

USDA NRCS. 2002. National Engineering Handbook, Part 637, Chapter 3, Constructed Wetlands.

Washington, D.C. https://directives.sc.egov.usda.gov/

USDA NRCS. 2020. “The PLANTS Database.” Accessed July 26, 2021. https://plants.usda.gov

Vymazak, J. and L. Kropfelova. 2009. Removal of Nitrogen in Constructed Wetlands with Horizontal SubSurface Flow: A Review. Wetlands. 29: 1114-1124.

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