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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. 

USDA is an equal opportunity provider, employer, and lender.

Natural Resources Conservation Service 

CONSERVATION PRACTICE STANDARD 

DAM, DIVERSION 

CODE 348 

(no)

DEFINITION 

A structure built to divert all or part of the water from a waterway or a stream. 

PURPOSE 

This practice is used to accomplish one or more of the following purposes: 

• Divert all or part of the water from a waterway in a controlled manner for beneficial use 

• Divert periodic flows from one watercourse to another watercourse 

CONDITIONS WHERE PRACTICE APPLIES 

This standard applies to structures of a permanent nature, constructed of materials having an expected

lifespan consistent with the designed purpose of the structure. 

This practice applies where— 

• A diversion dam is an integral part of an irrigation system or a water-spreading system. 

• Diversion of water from an unstable watercourse to a stable watercourse is desirable. 

• The water supply available is adequate to divert. 

This standard does not apply where NRCS Conservation Practice Standards (CPSs) Diversion (Code

362), Dam (Code 402), or Grade Stabilization Structure (Code 410) apply. 

CRITERIA 

General Criteria Applicable to All Purposes 

The installation and operation of this practice must follow applicable Federal, Tribal, State, and local laws,

rules, and regulations. Obtain all required permits before construction. 

Environmental impacts 

Evaluate the impacts of a proposed diversion dam on environmental resources including water quality, fish

and wildlife habitat, forest, and visual resources. Identify and address the techniques and measures

necessary to overcome any undesirable effects. 

Source water impacts 

Evaluate the impacts of a proposed diversion dam on sources of drinking water including water quality,

water quantity, and long-term water availability. Identify and document potential risks to sources of drinking

water and develop solutions to mitigate such risks. 
Materials 

All materials used to construct the diversion dam and appurtenances must have the strength, durability,

and workability needed to meet the installation and service conditions of the site. 

Structural design 

Design appurtenant structures to withstand all expected loads, including all required loads described by

NRCS National Engineering Manual (Title 210), Part 536, “Structural Engineering.” 

Outlet works 

For diverted flows, the outlet works must provide positive control for both maximum and minimum flow

rates consistent with the purpose of the diversion. The outlet works must provide safe diversion of all

expected flows, considering such hazards as the potential for erosion, cavitation, and reduction in flow

capacity due to the buildup of debris and sediments. 

Bypass works 

The bypass works must be capable of passing all flows needed to satisfy downstream priorities and all

flows greater than diversion requirements, including expected flood flows. This may require a combination

of orifices, weirs, and gates designed to meet the requirements of the site. The bypass works must

provide safe bypass of all expected flows, considering such hazards as the potential for erosion,

cavitation, and reduction in flow capacity due to the buildup of debris and sediment. 

Special-purpose works 

If debris, bed load materials, or sediments are present under flow conditions subject to diversion, make

provision to bypass or remove materials that may be detrimental to the functioning of the outlet works,

other parts of the works, or areas to where water is diverted. This may require the use of settling basins,

debris traps, trash guards, or sluiceways, depending on site conditions. 

Vegetation 

Vegetate disturbed areas, not otherwise covered or protected, as soon as practicable after construction.

Seed, fertilize, and mulch in accordance with NRCS CPS Critical Area Planting (Code 342). Consider

using a diverse mix of native vegetation that is adapted to the site to provide enhanced ecological habitat

and pollinator benefits. Protect the area from livestock and human traffic until the site is fully stabilized. If

soil or climatic conditions prevent the use of vegetation, use nonvegetative materials, such as mulches,

gravel, and rock riprap. 

Public safety 

Diversion dams often have public safety hazards such as hydraulic rollers downstream of weirs, high flow

velocity upstream of gate openings, and high vertical walls. Evaluate all structures for potential safety

hazards. Design means to minimize safety hazards when possible. Provide fences, railings, warning

signs, and other safety devices to prevent access to hazardous areas. 

CONSIDERATIONS 

Consider the effects of this practice on water quantity, water quality, and the environment. Consider— 

• Effects on the water budget on the volume and rate of runoff, infiltration, evaporation, transpiration,

deep percolation, and ground water recharge. 

• Effects of the use of diverted waters for irrigation. 

• Effects of the original watercourse on the newly constructed watercourse and on the areas

providing and receiving diverted water. 

• Effects on erosion and the movement of sediment, pathogens, and soluble and sediment-attached

substances carried by runoff. 

• Potential temperature changes in downstream waters resulting from reduced flows and differences

in bank shading in different watercourses. 

• Potential changes in quantities of soluble substances infiltrating the soil and available for ground

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water recharge, as well as the potential for salt pick-up. 

• Potential for introducing new plant or animal species to either the upstream or downstream waters. 

PLANS AND SPECIFICATIONS 

Prepare plans and specifications that describe the requirements for applying the practice according to this

standard. As a minimum, include— 

• A plan view of the layout of the diversion dam. 

• Typical profiles and cross sections of the diversion dam. 

• Details of the outlet system. 

• Structural drawings adequate to describe the construction requirements. 

• Requirements for vegetative establishment and mulching, as needed. 

• Safety features. 

• Site-specific construction and material requirements. 

OPERATION AND MAINTENANCE 

Prepare an operation and maintenance plan for the operator. 

At a minimum, include— 

• Periodic inspections of all structures, earthen embankments, spillways, and other significant

appurtenances. 

• Prompt removal of trash from pipe inlets and trash racks. 

• Prompt repair or replacement of damaged components. 

• Periodic removal of trees, brush, and undesirable species. 

• Periodic inspection of safety components and immediate repair if necessary. 

• Maintenance of vegetative protection and immediate seeding of bare areas as needed. 

• Repair of erosion adjacent to the structure. 

REFERENCES 

USDA NRCS. 2020. National Engineering Handbook (Title 210), Part 630, Hydrology. Washington, D.C.

https://directives.sc.egov.usda.gov/

USDA NRCS. 2017. National Engineering Handbook (Title 210), Part 633, Soil Engineering. Washington,

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

USDA NRCS. 2008. National Engineering Handbook (Title 210), Part 636, Structural Engineering.

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

USDA NRCS. 2012. National Engineering Handbook (Title 210), Part 650, Engineering Field Handbook.

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

USDA NRCS. 2017. National Engineering Manual (Title 210). Washington, D.C.

https://directives.sc.egov.usda.gov/

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