United States Department of Agriculture 428-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 

IRRIGATION DITCH LINING 

CODE 428 

(ft)

DEFINITION 

An irrigation ditch, canal, or lateral lined with an impervious material or a chemical treatment. 

PURPOSE 

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

• Improve the conveyance of irrigation water 

• Prevent waterlogging of land 

• Maintain water quality 

• Prevent erosion 

• Reduce water loss 

• Reduce energy loss 

CONDITIONS WHERE PRACTICE APPLIES 

This practice applies to constructed ditches that are part of an irrigation conveyance or distribution system

and are subject to erosion or excessive seepage. 

This practice applies to areas where irrigation systems are adequate and water supplies sufficient to make

deliveries practical for the types of crops grown and the methods of application used. 

This practice does not apply to natural streams. 

CRITERIA 

General Criteria Applicable to All Purposes 

Plan, design, and construct lined waterways to comply with all Federal, State, and local laws and

regulations. 

Identify areas where ditches are susceptible to damage from side drainage flooding, and adequately

protect these areas from such damage. 

Make provisions to protect the lining from external water pressures, frost-heave, chemical reactions with

the soil and water, animal damage, and fire. 

Establish lining thickness based on engineering considerations for each site. Evaluate location, canal

dimensions, velocity, subgrade conditions, the method of construction, operation, lining material, expected

life, and climate in determining canal lining thickness. 
Materials 

On sites where sulfate, salts, or other strong chemical concentrations exist and may cause damage to the

lining, ensure that the lining material is either compatible with, or protected from, the chemicals. 

Concrete 

For concrete liner design, follow criteria established in NRCS Conservation Practice Standard (CPS) Pond

Sealing or Lining – Concrete (Code 522). In addition, limit concrete lining in ditches to— 

• Bottom width not greater than 6 feet. 

• Flow capacities equal to or less than 100 cubic feet per second. 

• Design velocities equal to or less than 15 feet per second. 

Fly ash may be used to replace up to 25 percent of the cement by weight when other pozzolans are not

used. Meet the requirement of ASTM C-618, “Standard Specification for Coal Fly Ash and Raw or

Calcined Pozzolan for Use in Concrete.” 

An air entrainment admixture can be used to improve workability and reduce damage caused by freezethaw cycles. The air content by volume should be between 4 and 6 percent for a concrete mixture

containing a maximum aggregate size of less than 1 inch and 5 to 7 percent for a maximum aggregate

size greater than 1 inch. 

The water-cement ratio should be 0.50 plus or minus 0.05. 

Install concrete linings in soils with high sulfate concentrations in accordance with those values shown

below in table 1. 

Table 1. Cement Requirements for Concrete Exposed to Sulfates1 

1 Data taken from American Concrete Institute (ACI) 318, Tables 19.3.1.1 and 19.3.2.1. 

2 The amount of pozzolan or slag cement used should be at least the minimum amount determined by

service record to improve sulfate resistance in Type V cement. 

Ensure the minimum thickness for plain concrete linings in rectangular sections is 31⁄2 inches. For

trapezoidal or parabolic sections, ensure the minimum thickness is in accordance with table 2. 

Table 2. Minimum Required Thickness for Trapezoidal or Parabolic Sections, Plain Concrete Ditch, and

Canal Linings 

Water-soluble sulfate

(SO4

2-) percent by

weight

Dissolved sulfate (SO4

2-)

in water parts per million

Cement Type ASTM

C150

Cement Type ASTM

C595

SO4

2- < 0.10 SO42- < 150 Any Any

0.10 ≤ SO4

2- < 0.20 150 ≤ SO42- < 1,500 II Type IP, IS, or IT with

(MS) designation

0.20 ≤ SO4

2- ≤ 2.00 1,500 ≤ SO42- ≤ 10,000 V Type IP, IS, or IT with

(HS) designation

SO4

2- > 2.00 SO42- > 10,000 V plus pozzolan or slag

cement2

Type IP, IS, or IT with

(HS) designation plus

pozzolan or slag cement2

Design velocity1 

(ft/s)

Minimum thickness by climatic area2 (in)

Warm Cold

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1 Velocities in short chute sections will not be considered design velocity 

2 Climatic area designation: 

Warm – January average temperature is above 40 o • F 

Cold – January average temperature is below 40 o • F 

Steel and non-ferrous metal 

Protect steel and nonferrous metals subject to damage from soils or corrosive water with coatings,

cathodic protection, or other methods specifically designed to protect the liner. 

Ensure galvanized lining material meets the requirements of ASTM A653/A653M, “Standard Specification

for Steel Sheet, Zinc-Coated (Galvanized) or Zinc-Iron Alloy-Coated (Galvannealed) by the Hot-Dip

Process.” Ensure the minimum thickness of the lining material is 24 gauge for individual sheets 84 inches

or less in width and 22 gauge for wider sheets. Ensure the minimum thickness of steel sheets used in

bulkheads and related structures is 20 gauge. 

Roll or press the edges of the lining sheet into a shape that will provide added strength at the corners and

a firm anchorage into the ditch bank berm at the top of the lining. 

Ensure that fasteners and anchors used in the assembly of liners are zinc plated, cadmium plated,

stainless steel, or epoxy coated and that fasteners and linings are compatible according to the galvanic

series. Ensure joints are flexible, watertight, and filled with sealant material capable of withstanding

contraction and expansion of the lining material for the temperature variation expected at the site. 

Geosynthetic and semi-rigid formed plastic 

Protect geosynthetic and semi-rigid formed plastic linings from animal damage, excess heat, and fire. For

geosynthetic liners protected by earth or earth and gravel covering, ensure the covering is not less than 6

inches thick and extends a minimum of 6 inches above the top edge of the lining unless recommended

differently by the manufacturer. In areas subject to traffic by livestock, ensure the minimum thickness of

the protective cover is 9 inches and free of particles larger than three-eighths of an inch, angular particles,

and other sharp objects. 

Ensure the material in the bottom 3 inches of cover is free of particles larger than three-eighths of an inch,

angular rock particles, and other sharp objects. Lining in the bottom of the ditch may require thicker

material, as recommended by the manufacturer. 

Covered linings require cutoffs and anchor trenches to secure the lining to the subgrade. Exposed linings

require cutoffs and anchor trenches to secure the liner from uplift or tearing away from the bottom and

sides if the seams release. 

Ensure any exposed manufactured lining material has sufficient ultraviolet protection to prevent premature

deterioration. Install polyurethane/geotextile composite linings so they are only exposed during

installation, according to the manufacturer’s recommendations. 

The minimum required thickness for various lining materials should consider subgrade conditions,

hydrostatic forces, and susceptibility of the lining to damage during or after installation. 

Table 3. Minimum Required Thickness for Various Lining Materials 

Design velocity1 

(ft/s)

Minimum thickness by climatic area2 (in)

Less than 9.0 1.5 2.0

9.0–12.0 2.5 2.5

12.0–15.0 2.5 3.0

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1 Cover required (will not be installed exposed) 

 Key: PVC – polyvinyl chloride 

 GCL – geosynthetic clay liner 

 EPDM – ethylene propylene diene monomer (synthetic rubber) 

 HDPE – high density polyethylene 

 LLDPE – linear low-density polyethylene 

 PE – polyethylene 

 FPP – flexible polypropylene 

Chemical treatment 

Chemical treatment includes the application of chemical compounds to the surfaces of earthen ditches.

Bentonite or soil cement may be applied as treatment. Application requires the incorporation and

compaction of the combined soil and treatment mixture as specified by field performance data or

geotechnical laboratory reports. In the absence of these reports, apply treatment mixture at a rate equal to

or greater than the amount specified in table 4. Install the liner in maximum lifts of 6 inches. 

Table 4. Minimum Required Application Rate for Finished Compacted Lining for Chemical Treatment of

Ditches 

Material Minimum thickness (mil unless noted)

PVC1 30

GCL1 0.75 lb/ft2 sodium bentonite

EPDM 45

EPDM (reinforced) 45

Polyurethane/geotextile composite 45

HDPE 30

LLDPE 30

LLDPE (reinforced) 24

PE (reinforced) 24

FPP 30

FPP (reinforced) 24

Bituminous geomembrane 120

Chemical treatment 3 in

Compacted clay 3 in

Material Minimum application rate/compacted thickness

(lb/ft2)/(in)

TSPP1 0.0125

STPP1 0.0125

Soda Ash1 0.025

Bentonite1 See soil type

 Silts 0.375

 Silty sands 0.5

 Clean sands 0.625

Soil cement 1.25

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1 Cover required (will not be installed exposed) 

 Key: TSPP – tetrasodium pyrophosphate 

 STPP – sodium tripolyphosphate 

 Soda Ash – sodium carbonate 

 Bentonite – sodium bentonite (minimum free swell – 22 ml) 

 Soil Cement – a mixture of Portland cement, soil, and water 

Capacity 

Ensure lined ditches have adequate capacity to meet the requirements of its intended purpose without

damage or surpassing the design freeboard. For design purposes, compute capacity using Manning’s

formula based on maximum probable roughness condition with an “n” value not less than— 

• Concrete – 0.015. 

• Steel/nonferrous metal – 0.013. 

• Geosynthetic/SRFP (covered) – 0.025. 

• Geosynthetic/SRFP (exposed) – 0.011. 

• Chemical treatment – 0.025. 

Velocity 

For channels with noncovered concrete or metal linings, avoid unstable surge flows by limiting velocities

to 1.7 times the critical velocity in straight reaches that discharge into ditch sections or structures designed

to reduce the velocity to less than critical velocity. Ensure maximum velocity in these straight reaches is

less than 15 feet per second. 

When using geosynthetic linings, follow the manufacturer’s recommendations for velocity limitations. 

For channels with covered linings, evaluate the stability of the cover material by computing the velocity

using a Manning’s roughness coefficient “n” no greater than 0.025. 

When soil material is used as a protective cover over a liner, do not exceed the nonerosive velocity for the

soil material or the material through which the canal or ditch passes, whichever is less. Local information

on velocity limits for specific soils may be used if available. If such information is not available, base

stability limits on the tractive stress design approach found in USDA Agricultural Research Service

Agriculture Handbook Number 667, “Stability Design of Grassed-Lined Open Channels,” or other

comparable channel stability criteria. 

Ensure the ditch velocity for water delivered onto the field through gates, turnouts, siphon tubes, or similar

means is less than supercritical and sufficiently low to permit operation of the planned structure or device. 

Freeboard 

The required freeboard for a ditch can vary due to the ditch size and slope, materials used to construct the

ditch, cross slope, intercepted drainage area, alignment, rate of water surface elevation changes,

operation, and other site conditions. Ensure the minimum freeboard for any lined ditch or canal consists of

3 inches of lining above the design water surface. If the design velocity is within ±30 percent of critical

velocity, ensure the lined freeboard is at least 6 inches above the design water surface. 

The minimum freeboard requirement is based on the assumption that the finished channel bottom

elevation will vary by no more than 0.1 feet from the design elevation. If a construction deviation greater

than 0.1 feet is permitted, increase the minimum freeboard. Provide additional freeboard if required by

velocity, flow depth, alignment, obstruction, curves, and other site conditions. 

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Water surface elevation 

Design all lined ditches so the water surface elevations at field takeout points are high enough to provide

the required flow onto the field surface. If ditch checks or other control structures are used to provide

necessary head, include the backwater effect when computing freeboard requirements. 

The required elevation of the water surface above the field surface varies with the type of takeout

structure or device used and the amounts of water delivered. Provide a minimum head of 4 inches. Use

energy dissipation devices where erosion is anticipated at outlets. 

Ditch side slopes 

For the construction methods and materials shown below, ensure side slopes are no steeper than

indicated in table 5. 

Table 5. Side Slope Steepness in Various Construction Methods and Materials 

1H – Horizontal, V – Vertical 

For materials not listed above, follow the manufacturer’s recommendations. 

Ditch banks 

Shape ditch banks with earth to at least the top edge of the lining and provide necessary anchorage for

the top edge of the lining. In cut sections, other than in rock, construct a berm no less than 2 inches above

the top of the lining. Design banks and berms that are wide enough to ensure the stability of fills, the

lining, and to prevent excessive deposition in cut sections. 

When using siphon tubes, provide minimum berm or bank width of 12 inches at the top of the lining on

both sides of the finished ditch. Ensure all other canals and laterals have a minimum berm or bank width

of 18 inches at the top of the lining. 

If the bank or berm is to be used as a roadway, ensure the top width is adequate for the purpose. The

minimum recommended roadway width for straight sections is 12 feet. 

Ensure outside bank slopes and slopes above the berm elevation in cut sections are flat enough to ensure

stability. A minimum slope of 2H to 1V is recommended. Where vegetation will be maintained by mowing,

ensure the minimum slope is 3H to 1V. 

Related structures 

Provide adequate inlets, outlets, turnouts, checks, crossings, and any other related structures needed for

the successful management of irrigation water. Install structures so the capacity or the freeboard of the

ditch is not reduced, and the effectiveness of the lining is not impaired. 

Hand-placed, formed concrete

Height of lining less than 11⁄2 ft Vertical

Hand-placed, screeded concrete

Height of lining less than 21⁄2 ft 3⁄4H to 1V1

Height of lining more than 21⁄2 ft 1H to 1V

Slip-form concrete

Height of lining less than 3 ft 1H to 1V

Height of lining more than 3 ft 11⁄4H to 1V

Chemical treatment

Spray/stair-step applications 1H to 1V

Incorporation on slope 3H to 1V

Covered lining

Not less than 3H to 1V

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Install bulkheads for adequate anchorage that are formed to fit the lining, sufficient size to extend at least

12 inches into the earthen ditch pad for the entire width of the ditch lining, at the beginning and end of the

lining section, and at intervening points. 

CONSIDERATIONS 

The addition of fiber reinforcement increases the durability and reduces the potential for minor cracking in

concrete. 

Wetlands or water-related habitats may be adversely affected by the reduction of canal seepage. Changes

in vegetation growth along and near the conveyance system that are related to reduced seepage should

be monitored, mitigated, and addressed as necessary. 

Reduced canal seepage may have effects on the movement of dissolved substances into the ground

water. 

Changes in downstream flows may affect other water uses or users (e.g., drinking water supplies). 

Mitigate short-term and construction-related effects on air quality. 

PLANS AND SPECIFICATIONS 

Describe the requirements for applying the practice to achieve its intended purposes, to include— 

• A plan map showing the location of the lining for the different reaches. 

• Typical cross-sections. 

• Profiles. 

• Site-specific construction details. 

• Details for other structures installed with this practice. 

• Specifications that describe the installation and materials to be used. 

OPERATION AND MAINTENANCE 

Determine operation and maintenance requirements based on the site-specific design. As a minimum

include— 

• A schedule for regular inspections of the lining installation. 

• Removal of sediment and debris as required. 

• Patching or replacement of damaged sections of lining. 

• Other actions specific to the installation to ensure proper performance throughout the conservation

practice lifespan. 

REFERENCES 

ASTM A653/A653M. 2020. Standard Specification for Steel Sheet, Zinc-Coated (Galvanized) or Zinc-Iron

Alloy-Coated (Galvannealed) by the Hot-Dip Process. ASTM International, West Conshohocken, PA. DOI:

10.1520/A0653_A0653M-20. http://www.astm.org

ASTM C-618. 2019. Standard Specification for Coal Fly Ash and Raw or Calcined Pozzolan for Use in

Concrete. ASTM International, West Conshohocken, PA. DOI: 10.1520/C0618-19. http://www.astm.org

American Concrete Institute. 2006. 350-06 Code Requirements for Environmental Engineering Concrete

Structures. Farmington Hills, MI. ISBN: 9780870312274. https://www.concrete.org/

USDA NRCS. 1991. Design Engineering Technical Note (Title 210). Design Note No. 24, Guide for the

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

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