United States Department of Agriculture 378-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 

POND 

CODE 378 

(no)

DEFINITION 

A water impoundment made by constructing an embankment, excavating a dugout, or a combination of

both. 

In this standard, NRCS defines ponds constructed by the first method as embankment ponds and those

constructed by the second method as excavated ponds. Ponds constructed using a combination of the

excavation and embankment methods are classified as embankment ponds if the depth of water

impounded against the embankment at the auxiliary spillway elevation is 3 feet or more above the lowest

original ground along the centerline of the embankment. 

PURPOSE 

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

• Store water for: 

• Livestock 

• Fish and wildlife 

• Recreational use 

• Fire control 

• Erosion control 

• Flow detention 

• Improve water quality 

CONDITIONS WHERE PRACTICE APPLIES 

This practice applies to all excavated ponds. It also applies to embankment ponds that meet all criteria for

low-hazard potential dams as listed below: 

• The failure of the dam will not result in loss of life, damage to homes, commercial or industrial

buildings, main highways, or railroads, or in interruption of the use or service of public utilities. 

The product of the storage times the effective height of the dam is less than 3,000 acre-feet2 • .

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.

The effective height of the dam is the difference in elevation, in feet, between the lowest open

channel auxiliary spillway crest and the lowest point in the original cross section taken on the

centerline of the dam. If there is no open channel auxiliary spillway, use the lowest point on the top

of the dam instead of the lowest open channel auxiliary spillway crest. 

• The effective height of the dam is 35 feet or less. 
CRITERIA 

General Criteria Applicable to All Ponds 

Plan, design, and construct the pond to comply with all Federal, State, and local laws and regulations.

Notify landowners and/or contractor of their responsibility to locate all buried utilities in the project area,

including drainage tile and other structural measures. The landowner is also required to obtain all

necessary permits for project installation prior to construction. 

Design a minimum sediment storage capacity equal to the design life of the structure, or provide for

periodic cleanout. Protect the drainage area above the pond to prevent sedimentation from adversely

affecting the design life. 

Design measures necessary to prevent serious injury or loss of life according to the requirements of

NRCS National Engineering Manual (NEM) (Title 210), Part 503, “Safety.” 

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

areas disturbed during construction in accordance with the criteria in NRCS Conservation Practice

Standard (CPS) Critical Area Planting (Code 342). When necessary to provide surface protection where

climatic conditions preclude the use of seed or sod, use the criteria in NRCS CPS Mulching (Code 484) to

install inorganic cover material such as gravel. 

Cultural resources 

Evaluate the existence of cultural resources in the project area and any project impacts on such

resources. Provide conservation and stabilization of archeological, historic, structural, and traditional

cultural properties when appropriate. 

Site conditions 

Select or modify the site to allow runoff from the design storm to safely pass through a natural or

constructed auxiliary spillway, a combination of a principal spillway and an auxiliary spillway, or a principal

spillway. 

Select a site that has an adequate supply of water for the intended purpose through surface runoff, ground

water, or a supplemental water source. Water quality must be suitable for its intended use. 

Reservoir 

Provide adequate storage volume to meet user demands for all intended purposes. Account for

sedimentation, season of use, evaporation loss, and seepage loss when computing the storage volume. 

Additional Criteria for Embankment Ponds 

Geological investigations 

Use pits, trenches, borings, and reviews of existing data or other suitable means of investigation to

characterize materials within the embankment foundation, auxiliary spillway, and borrow areas. Classify

soil materials using ASTM D2487-17e1, “Standard Practice for Classification of Soils for Engineering

Purposes (Unified Soil Classification System).” Determine from the investigations if problem soils exist at

the embankment pond site for defensive design measures. Problem soils, include but are not limited to

dispersive clays, collapsible soils, soft clays, expansive clays, low internal erosion resistance soils, loose

coarse-grained soils, high soluble content soils, and caliche soils. 

Foundation cutoff 

Design a cutoff of relatively impervious material under the dam and up the abutments as required for

preventing seepage. Locate the cutoff at, or upstream from, the centerline of the dam. Extend the cutoff

deep enough to intercept flow and connect with a relatively impervious layer. Combine seepage control

with the cutoff as needed. Use a cutoff bottom width adequate to accommodate the equipment used for

excavation, backfill, and compaction operations. Design cutoff side slopes no steeper than one horizontal

to one vertical. 

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Seepage control 

Include seepage control if— 

• Foundation cutoff does not intercept pervious layers. 

• Seepage could create undesired wet areas. 

• Embankment stability requires seepage control. 

• Special problems require drainage for a stable dam. 

Filter zones may be required in some embankment designs to address the problem of cracking and

internal erosion of the embankment for sites with problematic conditions such as dispersive clays, steep

abutments, and other issues. 

Control seepage with— 

• Foundation, abutment, or embankment filters and drains. 

• Filter diaphragms. 

• Reservoir bottom blanketing. 

• A combination of these measures. 

Top width 

Table 1 provides the minimum top widths for dams of various total heights. Total height is the vertical

distance between the settled top of the dam and the lowest elevation at the downstream toe. 

Design a minimum width of 16 feet for one-way traffic and 26 feet for two-way traffic for the top of a dam

used as a public road. Design guardrails or other safety measures where necessary and follow the

requirements of the responsible road authority. For dams less than 20 feet in total height, maintenance

considerations or construction equipment limitations may require increased top widths from the minimum

shown in table 1. 

Table 1. Minimum Top Width for a Dam. 

Side slopes 

Design each side slope with a ratio of two horizontal to one vertical or flatter. Design the sum of the

upstream and downstream side slopes with a ratio of five horizontal to one vertical or flatter. As required,

design benches or flatten side slopes to assure stability of all slopes for all loading conditions. Flatter

slopes may be required for stability for some problematic embankment or foundation soils such as highly

plastic embankment soils or very soft clays. Downstream or upstream berms can be used to help achieve

stable embankment slopes. 

Slope protection 

Design special measures such as berms, riprap, sand-gravel, soil cement, or use special vegetation as

needed to protect the slopes of the dam from erosion. Use NRCS Engineering Technical Release (TR)

210-56, “A Guide for Design and Layout of Vegetative Wave Protection for Earth Dam Embankments,” and

TR-210-69, “Riprap for Slope Protection against Wave Action,” as applicable. 

 Total Height of Dam 

 (feet)

 Top Width 

 (feet)

Less than 10 6

10–14.9 8

15–19.9 10

20–24.9 12

25–35 15 

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Freeboard 

Design a minimum of 1 foot of freeboard between design high-water flow elevation in the auxiliary spillway

and the top of the settled embankment. Design a minimum 2 feet of elevation difference between the crest

of the auxiliary spillway and the top of the settled embankment when the dam has more than 20 acre

drainage area or more than 20 feet in effective height. Design a minimum of 1 foot of freeboard above the

peak elevation of the design hydrograph to the top of the settled embankment when the pond has no

auxiliary spillway. 

Settlement 

Increase the height of the dam by the amount needed to ensure that the settled top elevation of the dam

equals or exceeds the design top elevation. Design a minimum settlement allowance of 5 percent of the

total height of the dam associated with each dam cross section, except where detailed laboratory soil

testing and settlement analyses or experience in the area shows that a lesser amount is adequate. 

Principal spillway 

A pipe with needed appurtenances shall be placed under or through the dam, except where rock,

concrete, or other types of lined spillways are used, or where a vegetated or earth spillway can safely

handle the rate and duration of the design flow. 

Design a minimum of 6-inches difference between the crest elevation of the auxiliary spillway and the

crest elevation of the principal spillway when the dam has a drainage area of 20 acres or less. Design a

minimum of 1 foot difference when the dam has a drainage area of over 20 acres. 

Provide an anti-vortex device to handle pressure flow in the principal spillway pipe. Design the inlet and

outlet to function for the full range of flow and hydraulic head anticipated. 

Design adequate pipe capacity to discharge long-duration, continuous, or frequent flows without causing

flow through the auxiliary spillway. Design a principal spillway pipe with a minimum inside diameter of 4

inches. Design pipe with a minimum inside diameter of 1-1/4 inches for water supply pipes or for pipes

used for any other purpose. 

Design pipe using ductile iron, welded steel, corrugated steel, corrugated aluminum, reinforced concrete

(precast or site-cast), or plastic. Do not use cast iron or unreinforced concrete pipe if the dam is 20 feet or

greater in total height. 

Design and install pipe to withstand all external and internal loads without yielding, buckling, or cracking.

Design rigid pipe for a positive projecting condition. Design flexible pipe according to the requirements of

NRCS National Engineering Handbook (NEH) (Title 210), Part 636, Chapter 52, “Structural Design of

Flexible Conduits.” 

Design connections of flexible pipe to rigid pipe or other structures to accommodate differential

movements and stress concentrations. Design and install all pipes to be watertight using couplings,

gaskets, caulking, water stops, or welding. Design joints to remain watertight under all internal and

external loading, including pipe elongation due to foundation settlement. 

Design a concrete cradle or bedding for pipe if needed to reduce or limit structural loading on the pipe and

improve support of the pipe. 

Design outlet structures, such as cantilever pipe outlet sections and impact basins, to dissipate energy as

needed. 

Corrosion protection 

Provide protective coatings for all steel pipe and couplings in areas that have traditionally experienced

pipe corrosion or in embankments with saturated soil resistivity less than 4,000 ohm-cm or soil pH less

than 5. Protective coatings may include asphalt, polymer over galvanizing, aluminized coating, or coal tar

enamel. 

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Ultraviolet protection 

Use ultraviolet-resistant materials for all plastic pipe or provide coating or shielding to protect plastic pipe

exposed to direct sunlight. 

Cathodic protection 

Provide cathodic protection for coated welded steel and galvanized corrugated metal pipe where soil and

resistivity studies indicate that the pipe needs a protective coating and where the need and importance of

the structure warrant additional protection and longevity. If the original design and installation did not

include cathodic protection, consider establishing electrical continuity in the form of joint-bridging straps on

pipes that have protective coatings. Add cathodic protection later if monitoring indicates the need. 

Internal erosion 

Install filter diaphragms for internal erosion control or anti-seep collars to reduce hydraulic gradient along

the pipe extending through the embankment with inverts below the peak elevation of the routed

hydrograph when the effective height of the dam is 15 feet or greater. 

Filter diaphragms 

Design the filter diaphragm according to the requirements of 210-NEH, Part 628, Chapter 45, “Filter

Diaphragms.” Locate the filter diaphragm immediately downstream of the cutoff trench, but downstream of

the centerline of the dam if the foundation cutoff is upstream of the centerline or if there is no cutoff trench. 

To improve filter diaphragm performance, provide a drain outlet for the filter diaphragm at the downstream

toe of the embankment. Protect the outlet from surface erosion and animal intrusion. 

Ensure that the filter diaphragm functions both as a filter for adjacent base soils and as a drain to

intercept seepage. Materials for the filter diaphragm must meet the requirements of 210-NEH-Part 633,

Chapter 26, “Gradation Design of Sand and Gravel Filters”. 

Anti-seep collars can be used where the following soil and site conditions apply: 

• Embankment soils are documented to be non-dispersive by crumb testing or evidence that the site

is located in geologic formations that are known to be non-dispersive. 

• Soils tests show that embankment soils have a plasticity index (PI) equal to or greater than 15. 

• The water content of the soils at the time of construction is such that a 1/8-inch diameter thread 1/2-

inch long may be rolled out on a flat surface without breaking or falling apart. 

• Natural or excavated ground slopes transverse to the embankment centerline in the vicinity of the

conduit are no steeper than 2 horizontal to 1 vertical. 

• Laboratory or field tests show that the foundation soils left in-place under the embankment and

principal spillway are medium to very stiff in saturated consistency or medium dense to very dense

depending on if these soils are cohesive or cohesionless, respectively. 

When using anti-seep collars in lieu of a filter diaphragm, ensure a watertight connection to the pipe. Limit

the maximum spacing of the anti-seep collars to 14 times the minimum projection of the collar measured

perpendicular to the pipe, or 25 feet, whichever is less. Locate anti-seep collars no closer than 10 feet

apart. Use a collar material that is compatible with the pipe material. 

Design the collars to increase the seepage path along the pipe within the fill by at least 15 percent. 

Trash guard 

Install a trash guard at the riser inlet to prevent clogging of the pipe, unless the watershed does not

contain trash or debris that could clog the pipe. 

Pool drain 

Provide a pipe with a suitable valve to drain the pool area if needed for proper pond management or if

required by State law. The designer may use the principal spillway pipe as a pond drain if it is located

where it can perform this function. 

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Auxiliary spillways 

A dam must have an open channel auxiliary spillway, unless the principal spillway is large enough to pass

the peak discharge from the design hydrograph and the trash that comes to it without overtopping the

dam. The minimum criteria for acceptable use of a closed pipe principal spillway without an auxiliary

spillway consists of a pipe with a cross-sectional area of 3 square feet or more, an inlet that will not clog,

and an elbow designed to facilitate the passage of trash. 

Design the minimum capacity of a natural or constructed auxiliary spillway to pass the peak flow expected

from a total design storm of the frequency and duration shown in table 2, less any reduction creditable to

the principal spillway discharge and detention storage. 

Design the auxiliary spillway to safely pass the peak flow through the auxiliary spillway, or route the storm

runoff through the reservoir. Start the routing either with the water surface at the elevation of the crest of

the principal spillway or at the water surface after a 10-day drawdown, whichever is higher. Compute the

10-day drawdown from the crest of the auxiliary spillway or from the elevation attained from impounding

the entire design storm, whichever is lower. Design the auxiliary spillway to pass the design flow at a safe

velocity to a point downstream where the flow will not endanger the dam. 

A constructed auxiliary spillway consists of an inlet channel, a control section, and an exit channel. Design

the auxiliary spillway with a trapezoidal cross-section. Locate the auxiliary spillway in undisturbed earth or

in-situ rock. Design stable side slopes for the material in which the spillway is to be constructed. Design a

minimum bottom width of 10 feet for dams having an effective height of 20 feet or more. 

Design a level inlet channel upstream from the control section for the distance needed to protect and

maintain the crest elevation of the spillway. If necessary, curve the inlet channel upstream of the level

section to fit existing topography. Design the exit channel grade according to 210-NEH-628, Chapter 50,

“Earth Spillway Design,” or with equivalent procedures. 

Structural auxiliary spillways 

Design chute spillways or drop spillways according to the principles set forth in 210-NEH, Part 650,

“Engineering Field Handbook”; and 210-NEH, Section 5, “Hydraulics”; Section 11, “Drop Spillways”; and

Section 14, “Chute Spillways.” Design a structural spillway with the minimum capacity required to pass the

peak flow expected from a total design storm of the frequency and duration shown in table 2, less any

reduction creditable to the pipe discharge and detention storage. 

Additional Criteria for Excavated Ponds 

Runoff 

Design a minimum of 1 foot of freeboard above the peak elevation of the design hydrograph. Design a

pipe and auxiliary spillway that meets the capacity requirements of table 2. Consider runoff flow patterns

when locating the excavated pond and placing the spoil. 

Side Slopes 

In the excavated area, design side slopes that are no steeper than one horizontal to one vertical. 

Inlet Protection 

Protect the side slopes from erosion where surface water enters the pond in a natural or constructed

channel. 

Excavated material 

Place the material excavated from the pond so that its weight does not endanger the stability of the pond

side slopes and so that the soil will not wash back into the pond by rainfall. Dispose of excavated material

in one of the following ways: 

• Uniformly spread to a height that does not exceed 3 feet, with the top graded to a continuous slope

away from the pond. 

• Uniformly place and with side slopes assuming a natural angle of repose. Place excavated material

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at a distance equal to the depth of the pond, but not less than 12 feet from the edge of the pond. 

• Shape to a designed form that blends visually with the landscape. 

• Provide for low embankment construction and leveling of surrounding landscape. 

• Haul material offsite. 

 

Table 2. Minimum auxiliary spillway capacity 

 

CONSIDERATIONS 

Visual Resource Design 

Carefully consider the visual design of ponds in areas of high public visibility and those associated with

recreation. The shape and form of ponds, excavated material, and plantings are to relate visually to their

surroundings and function. 

Shape the embankment to blend with the natural topography. Shape the edge of the pond so it is

generally curvilinear rather than rectangular. Shape excavated material so the final form is smooth,

flowing, and fitted to the adjacent landscape rather than angular geometric mounds. If feasible, add

islands to provide visual interest and attract wildlife. 

Fish and Wildlife 

Locate and construct ponds to minimize the impacts to existing fish and wildlife habitat. 

When feasible, retain trees in the upper reaches of the pond and stumps in the pool area. Shape upper

reaches of the pond to provide shallow areas and wetland habitat. 

If operations includes stocking fish, use NRCS CPS Fishpond Management (Code 399). 

Watering ramp 

When wildlife or livestock need access to stored water, use the criteria in NRCS CPS Watering Facility

(Code 614) to design a watering ramp. 

Vegeation 

Stockpile topsoil for placement on disturbed areas to facilitate revegetation. 

Consider selecting and placing vegetation to improve fish habitat, wildlife habitat, and species diversity. 

Water Quantity 

Consider effects on components of the water budget, especially— 

Drainage area 

(acre)

Effective height of

dam1(feet)

Detention storage

(acre-feet)

Minimum design storm2

Frequency (years) Minimum duration

(hours)

20 or less 20 or less < 50 10 24

20 or less > 20 < 50 25 24

> 20 all < 50 25 24

All others all all 50 24

1. Defined above in “Conditions where Practice Applies.” 

2. Select rain distribution based on climatological region.

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• Effects on volumes and rates of runoff, infiltration, evaporation, transpiration, deep percolation, and

ground water recharge. 

• Variability of effects caused by seasonal or climatic changes. 

• Effects on downstream flows and impacts to the environment such as wetlands, aquifers, and social

and economic impacts to downstream uses or users. 

Water Quality 

Consider the effects of— 

• Erosion and the movement of sediment, pathogens, and soluble and sediment-attached

substances that runoff carries. 

• Short-term and construction-related effects of this practice on the quality of downstream

watercourses. 

• Water level control on the temperature of downstream water to prevent undesired effects on aquatic

and wildlife communities. 

• Wetlands and water-related wildlife habitats. 

• Water levels on soil nutrient processes such as plant nitrogen use or denitrification. 

• Soil water level control on the salinity of soils, soil water, or downstream water. 

• Earth moving potentially uncovering or redistributing toxic materials. 

• Livestock grazing adjacent to the pond. Consider fencing to prevent livestock activities having direct

contact with the pond and dam. 

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 pond and appurtenant features. 

• Typical profiles and cross sections of the principal spillway, auxiliary spillway, dam, and appurtenant

features, as needed. 

• Structural drawings adequate to describe the construction requirements. 

• Requirements for establishing vegetation or other ground surface protection, as needed. 

• Safety features. 

• Site-specific construction and material specifications. 

• Utility location and notification requirements. 

OPERATION AND MAINTENANCE 

Prepare an operation and maintenance plan for the operator. 

As a minimum, include— 

• Periodically inspect all structures, earthen embankments, spillways, and other significant

appurtenances. 

• Promptly repair or replace damaged components. 

• Promptly remove trash from pipe inlet and trash rack. 

• Promptly remove sediment when it reaches predetermined storage elevations. 

• Periodically remove trees, brush, and undesirable species. 

• Periodically inspect safety components and immediately repair if necessary. 

• Maintain vegetative protection and immediately seeding bare areas, as needed. 

• Pevent the establishment of woody vegetation on constructed embankment fill and around spillway

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appurtenances. 

 

REFERENCES 

American Society for Testing and Materials. ASTM D2487-17e1, Standard Practice for Classification of

Soils for Engineering Purposes (Unified Soil Classification System). West Conshohocken, PA. DOI:

10.1520/D2487-17E01

USDA NRCS. 2019. Engineering Technical Releases, TR-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. 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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