United States Department of Agriculture 362-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. 

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

Natural Resources Conservation Service 

CONSERVATION PRACTICE STANDARD 

DIVERSION 

CODE 362 

(ft)

DEFINITION 

A channel usually constructed across the slope with a supporting ridge on the lower side. 

PURPOSE 

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

• Intercept surface and shallow subsurface flow to reduce runoff and erosion. 

• Divert water away from sensitive areas, conservation practices, agricultural waste systems,

infrastructure, and other improvements. 

• Collect or direct water for storage, water spreading, water-harvesting systems, or treatment. 

CONDITIONS WHERE PRACTICE APPLIES 

This practice applies to all land uses where the soils and topography allow construction of a diversion with

a suitable outlet. 

CRITERIA 

General Criteria Applicable to All Purposes 

Capacity 

Design diversions to be used as temporary measures to convey the peak discharge from the 2-year

frequency, 24-hour duration storm. 

Design diversions to protect agricultural land or surface mine reclamation to convey the peak discharge

from a 10-year frequency, 24-hour duration storm. 

Design diversions to protect urban areas, buildings, roads, and animal waste management systems to

convey the peak discharge from a storm frequency consistent with the hazard involved, but not less than a

25-year frequency, 24-hour duration storm with a minimum freeboard depth of 0.3 feet. 

The diversion design depth is the maximum expected water depth resulting from the design storm plus

any required freeboard. The diversion design depth at a culvert crossing or grade stabilization structure

must equal the headwater depth for the culvert or structure design storm plus any required freeboard. 

Cross section 

The channel may be parabolic, V-shaped, or trapezoidal. The diversion side slopes are based on stability

and access requirements for maintenance. Where a supporting ridge is required to contain the design flow

plus any required freeboard in the channel, the minimum ridge top width is 3 feet. Design all farmable

ridge side slopes no steeper than 5 horizontal to 1 vertical (5:1) to allow safe operation of farming

equipment. For nonfarmable slopes, the steepest side slope allowable is 2:1 unless an analysis of site
specific soil conditions indicates that steeper slopes will be stable. The top of the constructed ridge at any

point must not be lower than the design depth plus the specified overfill for settlement. 

Channel stability and capacity 

Channel grades may be uniform or variable. Determine minimum depth and width requirements for

channel stability by using the procedures in the NRCS National Engineering Handbook (Title 210), Part

650, Chapter 9, “Diversions.” 

When the diversion will not have a rigid lining, design a stable channel based on the limiting stress on the

soil and vegetation such that soil particles will not be detached, and the vegetation will not be damaged.

The capacity of a vegetated diversion will be based on the densest and longest vegetation resulting in the

highest expected retardance. 

Protection against sedimentation 

Excess sediment accumulation in the diversion channel lessens hydraulic capacity, impedes flow, and

inhibits vegetation. For a contributing drainage area that produces a high sediment load, incorporate

measures to limit the accumulation of sediment in the channel by— 

• Installing or applying conservation practices such as land treatment, erosion control, cultural or

tillage, or structural measures in conjunction with or before diversion construction. 

• Increasing the diversion channel size to accommodate the estimated sediment accumulation (e.g.,

2-year, 10-year, or 25-year) unless the operation and maintenance plan specifically addresses the

periodic removal of sediment. 

Outlets 

Each diversion must have a safe and stable outlet with capacity to convey the design storm. The outlet

may be a grassed waterway, a lined waterway, a vegetated or paved area, a grade stabilization structure,

an underground outlet, a stable watercourse, a sediment basin, or a combination of these practices. To

protect the diversion from overtopping, the designed discharge capacity of outlets must be achieved below

the design depth of the diversion at their junction. When using an underground outlet, the diversion must

contain the design storm runoff, less any reduction creditable to the conduit discharge. The outlet must

convey runoff to a point where outflow will not cause erosion. Install vegetated outlets before diversion

construction to ensure establishment of stable vegetative cover in the outlet channel, unless additional

protective measures are used until the vegetation is established. 

Vegetative establishment 

For vegetated diversions, use the criteria in NRCS Conservation Practice Standard (CPS) Critical Area

Planting (Code 342) to establish vegetation. Select species suited to local site conditions and intended

uses, and common to the site or location. Use plant species that exhibit the capacity to achieve adequate

density, height, and vigor within an appropriate timeframe to stabilize the diversion. 

Establish vegetation on noncropped disturbed areas as soon as conditions permit. Use mulch anchoring,

nurse crop, rock, straw or hay bale dikes, fabric checks, filter fences, erosion control blankets, or runoff

diversion to protect the vegetation until it is established. Planting of a close-growing crop (e.g., small

grains or millet) on the contributing watershed prior to construction of the diversion can significantly

reduce the flow through the diversion during establishment. 

Lining 

If the soils or climatic conditions preclude the use of vegetation for erosion protection, nonvegetative

linings such as concrete, gravel, rock riprap, cellular block, turf reinforcement mats, or other approved

manufactured lining systems may be used. Design any lining in accordance with the criteria in NRCS CPS

Lined Waterway or Outlet (Code 468). 

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CONSIDERATIONS 

A diversion in a cultivated field should be in alignment with other structures or practices in the field and

spaced in such a way as to facilitate safe and efficient use of farming equipment. The side slope lengths

should be sized to fit equipment widths when cropped. 

For a diversion protecting an agricultural waste system, infrastructure, or a sensitive area, consider

designing a wider ridge top, and consider greater channel freeboard. 

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. 

Diversion of storm runoff or subsurface seepage from a wetland may convert the wetland by changing the

hydrology. In analyzing downslope impacts, avoid adverse effects to existing wetland functions and

values. Consider how to maintain wetland functions and values with the diversion design. 

Hillside seeps in a crop field can cause cropping problems. Consider aligning the diversion and installing

subsurface drainage to intercept and correct seepage problems. Install the drainage prior to diversion

construction in accordance with NRCS CPS Subsurface Drain (Code 606). 

Any construction activities should minimize disturbance to wildlife habitat. Opportunities should be

explored to restore and improve wildlife habitat, including habitat for threatened, endangered, and other

species of concern. At noncropland sites, consider planting native vegetation in areas disturbed during

diversion construction. 

For vegetated diversions, avoid areas where subsurface, subsoil, or substratum material that limits plant

growth (such as by salts, acidity, root restrictions, etc.) may be exposed during implementation of the

practice. Where these areas cannot be avoided, seek recommendations from a soil scientist for improving

the conditions. Consider stripping and stockpiling the topsoil for spreading over the disturbed area to

facilitate vegetative establishment. 

Consider impacts to water quality when concentrating flows with a diversion and the potential need to treat

contaminated water. 

PLANS AND SPECIFICATIONS 

Prepare plans and specifications for the diversion that describe the requirements for applying the practice

according to this standard. As a minimum, the plans and specifications must include— 

• A plan view of the layout of the diversion. 

• Typical cross sections of the diversion. 

• A profile of the diversion that includes both the channel bottom and any supporting ridge top. 

• Construction specifications describing any site-specific details of installation such as— 

• Method of quantity measurement. 

• Placement requirements for any earthfill. 

• Disposal requirements for any excess soil material. 

• Seeding requirements for any vegetation to be established. 

• Lining requirements for any liner to be installed. 

OPERATION AND MAINTENANCE 

Prepare an operation and maintenance plan for use by the client. Include specific instructions for

maintaining diversion capacity, storage of runoff water, ridge height, and outlets in the plan. 

As a minimum, include— 

• Conducting periodic inspections, especially immediately following significant storms. 

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• Promptly repairing or replacing damaged diversion components as necessary. 

• Maintaining diversion capacity, ridge height, and outlet elevations, especially if high sedimentyielding regions are present in the drainage area above the diversion. Establish necessary

diversion cleanout requirements. 

• Periodically removing accumulated sediment so the outlet remains at the lowest point of the

channel. 

• Periodically mowing to maintain the desired vegetation height and design parameters. 

• Applying supplemental nutrients as needed to maintain the desired composition of vegetative

species and stand density in the diversion. 

• Controlling trees, brush, and noxious weeds by hand, chemical, and mechanical means as

necessary. 

• Scheduling maintenance outside of the primary nesting season for grassland birds. 

• Controlling pests that interfere with the timely establishment of vegetation. 

• Informing operators of potential hazards associated with operating equipment near steep-sloped

ridges. 

REFERENCES 

USDA NRCS. 2009. National Engineering Handbook (Title 210), Part 650, Chapter 9, Diversions.

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

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