United States Department of Agriculture 410-CPS-1

NRCS, NHCP

October 2020

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 

GRADE STABILIZATION STRUCTURE 

CODE 410 

(no)

DEFINITION 

A structure used to control the grade in natural or constructed channels. 

PURPOSE 

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

• Reduce erosion 

• Improve water quality 

CONDITIONS WHERE PRACTICE APPLIES 

This practice applies where channels require a structure to stabilize the grade or to control gully erosion. 

CRITERIA 

General Criteria Applicable to All Purposes 

Plan, design, and construct this practice to comply with all Federal, State, and local regulations. 

Set the crest of the inlet at an elevation that will stabilize the channel and prevent upstream head cutting. 

Design earthen embankments and auxiliary spillways to handle the total capacity flow indicated in tables 1

or 2 without overtopping any embankment. The foundation preparation, compaction, top width, and side

slopes must ensure a stable earthen embankment for anticipated flow conditions. 

Provide a minimum sediment storage capacity equal to the expected life of the structure, or provide for

periodic cleanout. 

Provide measures necessary to prevent serious injury or loss of life such as protective guardrails, warning

signs, fences, or lifesaving equipment. 

Seed or sod the exposed surfaces of earthen embankments, earth spillways, borrow areas, and other

areas disturbed during construction in accordance with NRCS Conservation Practice Standard (CPS)

Critical Area Planting (Code 342). If climatic conditions preclude the use of seed or sod, use NRCS CPS

Mulching (Code 484) to install inorganic cover material such as gravel. 

 

Table 1. Design Criteria for Establishing Minimum Capacity of Full-flow Open Structures 
Table 2. Design Criteria for Establishing Minimum Capacity of Side-inlet, Open-weir, or Pipe-drop

Drainage Structure 

Embankment dams 

Low-hazard dams that have a product of storage times the effective height of the dam of 3,000 ac-ft2 or

more, those more than 35 feet in effective height, and all significant and high-hazard dams must meet or

exceed the criteria specified in NRCS Engineering Technical Release (Title 210), 60, “Earth Dams and

Reservoirs.” 

Low-hazard dams that have a product of storage times the effective height of the dam of less than 3,000

ac-ft2 and an effective height of 35 feet or less must meet or exceed the requirements specified in NRCS

CPS Pond (Code 378). 

The effective height of the dam is the difference in elevation, in feet, between the auxiliary spillway crest

and the lowest point in the cross section along the centerline of the dam. If there is no auxiliary spillway,

the top of the dam is the upper limit. 

Storage is the capacity of the reservoir in acre-feet below the elevation of the crest of the lowest auxiliary

spillway or the elevation of the top of the dam if there is no open channel auxiliary spillway. 

Pond-sized dams 

If mechanical spillways are required, the minimum capacity of the principal spillway must convey the peak

flow expected from a 24-hour duration design storm of the frequency shown in table 3, less any reduction

from detention storage. For dams with effective height less than 20 feet, a stable auxiliary spillway with no

overfalls, and good auxiliary spillway vegetation along its reentry into the downstream channel, the

designer may reduce the principal spillway capacity to no less than 80 percent of the 2-year frequency, 24-

hour duration storm. For dams with a storage capacity more than 50 acre-feet or criteria values

exceeding those shown in table 3, use the 10-year frequency, 24-hour duration storm as the minimum

design storm. 

 

Table 3. Design Criteria for Establishing Minimum Capacity of the Principal Spillway for Dams with

Storage Capacity of Less than 50 acre-feet 

Maximum drainage area for indicated rainfall in a 5-

year frequency, 24-hour duration storm

Frequency of minimum design,

24-hour duration storm

0–3 inches 3–5 inches 5+ inches Vertical drop

Principal

spillway

capacity

Total capacity

acres feet year year

1,200 450 250 0–5 5 10

2,200 900 500 0–10 10 25 

Maximum drainage area for indicated rainfall in a 5-

year frequency, 24-hour duration storm

Frequency of minimum design,

24-hour duration storm

0–3 inches 3–5 inches 5+ inches Vertical drop Receiving

channel depth Total capacity

acres feet feet year

1,200 450 250 0–5 0–10 5

1,200 450 250 5–10 10–20 10

2,200 900 500 0–10 0–20 25

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NRCS, NHCP

410

October 2020
Small pond-sized dams 

For dams with an effective height of less than 15 feet and 10-year frequency, 24-hour storm runoff volume

less than 10 acre-feet, the designer may use the requirements of NRCS CPS Water and Sediment Control

Basin (Code 638). Design the grade control structure to control the peak flow from the 10-year frequency,

24-hour duration storm without overtopping. If the combination of storage and mechanical spillway

discharge will handle the design storm, an auxiliary spillway is not required. 

Full-flow open structures 

Design drop, chute, and box inlet drop spillways to the guidance in the NRCS National Engineering

Handbook (Title 210), Part 650, “Engineering Field Handbook” and other applicable NRCS publications

and reports. Provide a minimum capacity to pass the peak flow expected from a design storm of the

frequency and duration shown in table 1, less any reduction from detention storage. If site conditions

exceed those shown in table 1, design the minimum principal spillway capacity for the 25-year frequency

(24-hour duration) storm and design the minimum total capacity for the 100-year frequency (24-hour

duration) storm. Structures must not create unstable conditions upstream or downstream. Install

provisions for reentry of bypassed storm flows. The ratio of the capacity of drop boxes to road culverts

must meet the requirements of the responsible road authority or as specified in table 1 or 2, as applicable,

less any reduction from detention storage, whichever is greater. The drop box capacity (attached to a new

or existing culvert) must equal or exceed the culvert capacity at design flow. 

Island-type structures 

Design the minimum capacity equal to the capacity of the downstream channel. Design the minimum

auxiliary spillway capacity equal to that required to pass the peak flow expected from a 24-hour duration

storm of the frequency shown in table 1 for total capacity without overtopping the headwall extensions of

the mechanical spillway. Make provision for safe reentry of bypassed flow as necessary. 

Side-inlet, open weir, or pipe-drop drainage structures 

Table 2 provides the design criteria for minimum capacity of open-weir or pipe structures used to lower

surface water from field elevations or lateral channels into deeper open channels. Design the minimum

principal spillway capacity equal to the design drainage curve runoff for all conditions. If site condition

values exceed those shown in table 2, use the 50-year frequency, 24-hour duration storm for minimum

design of total capacity. 

CONSIDERATIONS 

Provide sufficient discharge to minimize crop-damaging water detention. 

In highly visible public areas and those associated with recreation, give careful consideration to landscape

resources. Landforms, structural materials, water elements, and plant materials should complement their

surroundings visually and functionally. Consider using a diverse mix of native vegetation that is adapted

to the site to provide enhanced ecological, habitat, and pollinator benefits. Shape excavated material and

cut slopes to blend with the natural topography. Shape shorelines and create islands to add visual interest

and wildlife habitat. Form and finish exposed concrete surfaces to add texture, reduce reflection, and to

alter color contrast. Select sites to reduce adverse impacts or create desirable focal points. 

Maximum drainage area for indicated rainfall in a 5-year

frequency, 24-hour duration storm

Effective height of

dam

Frequency of

minimum design,

24-hour duration

storm 0–3 inches 3–5 inches 5+ inches

acres feet year

200 100 50 0–35 2

400 200 100 0–20 2

400 200 100 20–30 5

600 400 200 0–20 5

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NRCS, NHCP

410

October 2020
Consider the effect of the grade control structure on aquatic habitat. For channels supporting fish,

consider the effect of the structure on fish passage. 

In natural channels, consider the effect of the grade control structure on fluvial geomorphic conditions. 

Provide fences to protect structures, earth embankments, and vegetated spillways from livestock. Near

urban areas, provide fencing as appropriate to control access and exclude traffic. 

PLANS AND SPECIFICATIONS 

Prepare plans and specifications for installing grade stabilization structures that describe the requirements

for applying the practice according to this standard. As a minimum, include— 

• A plan view of the layout of the grade stabilization structure and appurtenant features. 

• Typical profiles and cross sections of the grade stabilization structure and appurtenant features as

needed. 

• Structural drawings, as needed. 

• Seeding requirements, as needed. 

• Safety features. 

• Site-specific construction requirements. 

OPERATION AND MAINTENANCE 

Prepare an operation and maintenance plan for the operator. As a minimum, include— 

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

appurtenances. 

• Prompt repair or replacement of damaged components. 

• Prompt removal of sediment when it reaches predetermined storage elevations. 

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

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

Require maintenance of vegetative protection and immediate seeding of bare areas as needed. 

REFERENCES 

USDA NRCS. 2019. Engineering Technical Release (Title 210), 60, Earth Dams and Reservoirs.

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

USDA NRCS. 2008. National Engineering Handbook (Title 210), Part 628, Dams. 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

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NRCS, NHCP

410

October 2020