NATURAL RESOURCES CONSERVATION SERVICE fence specs.pdf

382(h)-1

Conservation practice specifications are reviewed periodically and updated if needed. To obtain the current version of this specification contact the Natural Resources Conservation Service.

NRCS Nevada February 2002

NATURAL RESOURCES CONSERVATION SERVICE

CONSERVATION PRACTICE SPECIFICATION

LET-DOWN FENCING, WATER GAPS,

CATTLE GUARDS, AND OTHER FENCE COMPONENTS

(FEET)

CODE 382(h)

I. SCOPE

The work shall consist of furnishing materials and installing fence components at the location(s) shown on the plan map and, if needed, on the drawings or as staked in the field.

Fencing includes brace assemblies, gates, cattle guards, and other components required to meet site conditions and achieve objectives for practice application.

II. CONSIDERATIONS

Let-down fences are designed for mountainous areas with heavy snow pack that can loosen or break fence wires and pull over fence posts.

This fence design also offers unhindered movement to big game and is suited for use where seasonal movements of big game is to be allowed for. To accommodate passage of resident big game while the fence span is upright, the top line wire is set at no more than 42-inches and the bottom wire is set at least 16-inches above the ground line.

Although let-down fences greatly reduce fence damage due to snow or wildlife, several disadvantages of this fence design should be noted: (1) cannot protect against stray or trespass livestock when fence is down;

(2) must be raised and lowered each year; and, (3) over winter contact with the ground corrodes fence wire more quickly.

Water gaps control livestock where fence lines cross streams or drainage ways.

Flood gates are installed in low areas of a fence line that are subject to flash flooding.

Cattle guards are metal structures constructed over a excavated pit. Gates should be constructed next to cattle guards to allow for livestock access and wildlife.

MATERIALS

All materials will be new, unless an exception is noted, with a minimum life expectancy of at least 10-years.

Where appropriate, all materials used for installation and not specifically listed below shall be in accordance with the requirements set forth for standard post-and-wire fence.

II. SPECIFICATIONS

LET-DOWN FENCE

The let-down fence is basically a four-strand barbed-wire fence that can be laid on the ground during winter after the grazing season or during periods of expected big game movement, but remains under tension at all times. See Exhibits 1 and 2.

With let-down fencing, line posts remain set but wood or metal stubs are used to attach line wires to each line post.

� If wood stubs are used, they must be at least

46-inches long and have a 2-inch top diameter.

� Steel stubs must be at least 46-inches long and meet the material quality specifications for steel line posts set forth for conventional post-and-wire fence.

CATTLE GUARD

Cattle guard grids shall be fabricated of the structural steel shapes shown in Exhibit 5 or other drawings approved by the State Resource Conservationist.

All structural steel shall conform to current ASTMA-7 specifications. All welds shall be secure and complete along both edges of the cross pieces and at all frame joints. All structural steel and welds shall be given at least one coat of rust proofing paint after fabrication is completed. All bolts, nuts, and washers shall be galvanized.

Cattle guards fabricated using pipe rails do not meet practice specification requirements.

Commercially fabricated cattle guards are acceptable for use providing:

� Such structures are designed for, and will support, H-20 loading. H-20 loading refers to a gross vehicle weight of 20-tons based on a weight distribution of 4,000-pounds on each side of the front axles and 16,000-pounds on each side of the rear axles.

� The structures are all steel and welded construction.

� The structures are of the nominal overall dimensions as shown in Exhibit 5. Powder River Model H-20 and Lincoln Steel Corporation Super Duty Autogate (both with clean-out sections), or their equal, meet practice specification requirements.

382(h)-2

NRCS Nevada February 2002

CONSTRUCTION SPECIFICATIONS

Unless otherwise specified, all construction requirements for installing posts, wire, and fasteners shall be in accordance with the specifications set forth for standard post-and-wire fence.

LET-DOWN FENCE

ALIGNMENT

Let-down fence spans shall be planned and constructed as straight stretches.

FENCE HEIGHT

The intended use of the fence determines fence height and line wire spacing. The minimum height (measured from the ground at post locations) of conventional post-and-barbed wire fences shall not be less than 36-inches.

IN-LINE BRACE UNITS

In-line brace assemblies are critical to the let-down fence design as they support the span that will be let down.

� In-line fence brace assemblies shall be separated by no more than 180-feet.

Line wire strands are stretched between brace posts.

Construction will allow each section between brace units (anchor points) to be laid down.

LINE POSTS

Line posts may be wood or steel.

Line posts remain set, but wood or metal stubs are used to attach line wires to each line post.

See Exhibit 1.

Line wires are stapled or clipped to the stubs.

Loops of No. 9-gauge, galvanized, wire are stapled at the bottom and top of wood line posts or are attached through holes drilled in steel posts. These wire loops are used to hold stubs to the line posts during the period when fence is upright.

When a fence section is let down, each stub should remain attached to the bottom wire loop of its associated line post so animals do not become entangled in the wire. See Exhibit 2.

The fence is raised by placing the upper end of the stubs in the top loops of line posts.

LINE POST SPACING is the same for all line post materials (metal, wood, etc.): Line post intervals shall be as follows:

� 3-wire fence

- 16½-feet (1 rod) maximum line post interval.

� 4-wire fence

- 20-foot maximum line post interval without stays.

- 25-foot maximum line post interval when one stay is set mid-way between line posts.

- 30-foot maximum line post spacing when two stays are set at 10-foot intervals between posts.

In heavy snow country, wooden posts should be spaced at no more than 16½-foot (1 rod) intervals to assure strength.

STAYS

When required, stays shall be evenly spaced between line posts to ensure that the proper interval between line wire strands is maintained.

FLOOD GATES AND WATER GAPS

Functional flood gates can be fabricated of one or more panels of pressure-treated boards fastened together with high-tensile wire and staples, or with wood stays and galvanized nails. The panels can be formed to fit the contour of the slope on either side of the drainageway or segmented to swing only in areas subjected to flooding.

The panels can also be suspended with loops of high-tensile wire from a horizontal cable consisting of a double wrap of high-tensile wire strung between the line posts on either side of the drainageway. These line posts should be diagonally wired to the adjacent post. See Exhibit 3.

Fence lines that cross streams may be damaged during heavy runoff periods unless water and water-born debris are allowed to pass under the fence.

An engineer should be consulted to assist in planning for water gap placement and appropriate water gap design.

There are two basic types of water gaps: for areas with very little water and only occasional flooding, a breakaway fence will be sufficient. In areas with regular flooding, water gap fencing should be constructed using floating gates or panels.

For depressions less than 16-feet wide, fence across the depression with no braces. For depressions greater than 16-feet wide, construct a fence that will breakaway only in the depression and leave the reaming fence sections undamaged. On wide drainageways brace units are constructed on either side of the depression and a separate fence section is installed within the drainageway. The end posts of the breakaway section are set 6 to 12-inches from the brace posts and attached to the main fence brace units with a light gauge wire. The light gauge tie wire will break if the fencing in the depression fails and damage to the main fence line is avoided.

Post material and dimensions, wire, and wire spacing for the water gap fence section are the same as for the main fence. Posts within the breakaway section can be set less than 12-inches deep to prevent post damage should the fence in the depression fail. See Exhibits 3 and 4.

Where a fenced depression receives regular flooding, a swinging or floating panel can be installed. This panel must be free to swing as water flows through the drainageway. Cross braces are constructed downstream of the swinging panel to offer a smooth edge for debris to pass by.

Although most water gaps and flood gates are designed to be self-cleaning it is necessary to check water gaps and flood gates after heavy flooding.

382(h)-3

February 2002

CONSTRUCTION SPECIFICATIONS (continued)

CATTLE GUARDS

Cattle guards shall be installed at right angles to the roadway.

Cattle guard bases shall be of reinforced concrete.

The cattle guard base shall have provision for drainage of the pit excavated for cattle guard placement.

All concrete shall be Class A, either ready-mix or field-mix.

Reinforcing bars shall be deformed intermediate grade.

Forms shall be used wherever necessary to shape concrete to required lines. Exposed concrete edges shall have a 1-inch x 1-inch chamfer.

Poured concrete is to be protected from freezing during the first 72 hours after placement.

Backfill material shall be placed around the concrete to the finish grade. Backfill material is to be free from rock fragments larger than gravel-size and excess organic matter. Backfill is placed in layers not to exceed 6-inches in thickness and is either hand-tamped or machine compacted. See Exhibit 6.

Cattle guards shall be securely bolted to their base.

See Exhibit 6 for recommended cattle guard wing construction (if metal wings are not part of cattle guard structure) and for fence line connections.

OTHER FENCE COMPONENTS

Materials used will follow Nevada NRCS Standards and Specifications for the standard post-and-wire fence conservation practice as appropriate.

Installation of fence components shall follow construction specifications presented in the USDAS/USDI publication Fencing. 2400-Range 8824 2803 unless otherwise stated above.

IV. INSTALLATION

Installation of cattle guards and other fence components shall conform to the specifications and Exhibits or other drawings, as provided.

The completed job shall be workmanlike and present a good appearance. The installer and other persons will

V. BASIS OF ACCEPTANCE

After the fencing and all fence components have been installed, a site inspection will be made to determine if construction, and the materials used, meet practice specification requirements.

VI. MAINTENANCE

This practice will require the performance of periodic maintenance.

Cattle guard pits must be cleaned out periodically to prevent debris from accumulating below the grates.

Check water gaps and flood gates after heavy flooding.

Fence maintenance items to be alert to and corrected include:

� broken stubs � bent or broken stays � stub wires broken � bent steel posts � wire corrosion � post alignment � tension of wire � post stability � broken line wires � sagging gates � pulled staples or clips

REFERENCES

The following references provide excellent guidance for fence construction, selection of fencing materials, and the installation of fence components such as brace assemblies, cattle guards, gates, rock jacks and wire cribs.

Henderson, G.E. Planning Farm Fences. American Association for Agricultural Engineering and Vocational Agriculture. June 1966.

Sanderson, R. et al. Specifications for Structural Range Improvements. General Technical Report PNW-GTR-250. USDA Forest Service-Pacific Northwest Research Station. September 1990.

Valentine, J.F. Range Developments and Improvements. Bringham Young Univ. Press. 1971.

USDI Bureau of Land Management and USDA Forest Service. Fencing. 2400-Range 8824 2803. July 1988.

382(h)-4

February 2002

Stay

Nicropress sleeve

1½" (min.) stapleLine post

Staple No. 9-gauge wire looped at top and bottom (loose at bottom). Staple lower loop to stay.

Leave enough slack in loop to hold or release stay.

Stays

Wires not stretched

Wire loops See Inset A

4'-6"

24"

6'-6"

5'-6" 5'-6" 5'-6"

16'-6"

12"

11"

10"

16"

STAY LET-DOWN FENCE

EXHIBIT 1

STAPLE LET-DOWN FENCE

Staple key

Driven staple

Driven staple

Strain insulators See Inset C

Wire splice- barbed wire to smooth wire

16'-6" 10'-0" 8'-0"

LET-DOWN FENCES

Inset C

Strain Insulator Solid tie to post

Smooth wire to let out and take up slack

See Inset B

Inset B Detail of Staples

USDI/USFS 2400-Range 8824 2803 (1988)

This fence configuration allows fence sections to lay on the ground. Line posts remain set. The bottom of stays are attached to the posts so animals do not become entangled. As fence wires contact the ground, wires tend to corrode quickly.

NOTE: Steel posts may also be used

This fence configuration allows all fence line wires to be lowered on the line posts by letting the slack out of each wire temporarily. Wire tension is reapplied to raise fence.

Inset A

382(h)-5

EXHIBIT 2

NRCS Nevada February 2002

About 15-ft

Anchor point may be a tree, corner-jack, or in-line brace unit

This section can be attached to an anchoring structure that is part of a standard wire fence

Let-down span length maximum of ¼-mile, depending on terrain

4-in x 6-in

No. 9-gauge wire

Secure wire to both components so that let-down fence span remains attached when it is down. Use No. 9-gauge wire.

Anchor point may be a tree, corner-jack, or in-line brace unit

Tension cables – ¼-in steel cable wrapped around anchor points and secured with two wire clamps. Use two separate cables on each span end. Cables must be placed on the let-down side of the wire

LET-DOWN FENCE

USDI/USFS 2400 –Range 8824 2803 (1988)

Sanderson et al (1990)

ANCHORING OF LET-DOWN FENCE

LET-DOWN FENCE

382(h)-6

February 2002

EXHIBIT 3

USDI/USFS 2300-Range 8824 2803 (1988)

F S

Double wrap of high-tensile wire

Direction of flow

Double wrap of

L

For fence line crossing o areas subject to flash flood

<16-ft

For depressions more than 16-ft wide, brace units need to be installed on either side of drainageway Direction of flow high-tensile wire

WATER GAPS

For control of livestock where fence lines cross streams or drainageways ight gauge wire

Examples of "breakaway" type water gap fencing:

For areas with very little water and only occasional flooding.

Use flood gate type panels in areas with regular f low s.

flooding.

LOOD GATE

FLOOD GATES AND WATER GAPS

Set 12" post depth to reduce damage to posts should fence in draw fail

382(h)-7

6" space Fencing in wide depressions that will prevent damage to the main fence line in case of flooding or deep snow accumulation.

6" space Brace unitBrace unit

>16-ft

2½" x 6" picket boards - install with 2' x 10" "U" Clamps. 1" pipe supported by 5/8" cable (inside

Deadman

SWING FENCE

No

EXHIBIT 4

USDI

pipe). 1¼" pipe spacers keep boards at installed location.

Lift fencing above water to avoid ice damage

Brace post Anchor to deadman

. 9-gauge wire

Light gauge tie wire NRCS Nevada February 2002

Large stay

Wire stay

Wire tie downs

Rocks

In-line brace unit

WATER GAPS

Poles can be used rather than large rocks. Panels can be made of woven wire or boards. Tie panel ends with light gauge wire so during flood periods one or both ends of the gap fencing will break loose without damaging the main fence line.

/USFS2300-RANGE 8824 2803 (1988)

382(h)-8

February 2002

EXHIBIT

G E

N E

R A

L N

O T

E S

T hi s pr oj ec t sh al l be co ns tr uc te d us in g S

C S

C on st ru ct io n S pe ci fi ca ti on

N o.

2.

C on cr et e an d N o.

1.

M et al

Fa br ic at io n.

T hi s sp ec if ic at io n is at ta ch ed t o th is d ra w in g an d sh al l be pa rt o f th is p la n.

A ll ex po se d m et al sh al l be g al va ni ze d.

A ll re in fo rc in g m et al s ha ll be ba rs a t i nc he s

O .C

. b ot h w ay s.

SC

S-

EN

G

-3

A R

EV

. 8

/7

382(h)-9

CONCRETE FOUNDATION

EXHIBIT 6

3-ft

Secure fence to end-barrier as needed to prevent passage of livestock.

t

Detail A Finished grade Set at road grade

Subgrade

1½"1½"

1½"

11"

8 2" x 2" x ¼" angle iron (galvanized after fabrication)

½" x 5" welded stud 24" C-C

Two No. 4 bars @ 8-ft 11"

Cattle Guard Width MATERIALS REQUIRED 14-ft 16-ft 24-ft

Concrete 3.3-yd3 3.7-yd3 5.4- yd3

No. 4 reinforcing steel bars 324-l.f. 355-l.f. 486-l.f.

2-in x 2-in angle iron 28-l.f. 32-l.f. 48-l.f.

E

USDI/USFS 2300-Range 8824 2803 (1988) 3-f -ft 6-in

Wooden end-barr barrier should be will adhere to tre white reflectors.

2" x 6" x 7' 6"

14"

11"

31"

Five No. 4 steel bars each footing

SECTION AT ROA

s

C

ND-BARRIER

3-ft No. 4 ties 14"

D CENTER

No. 4 stirrup

DETAIL A

6" NRCS Nevada February 2002 ier for cattle guard. End-painted white with paint that ated wood and marked with

10" diameter pole or 8" x 8" post

2" x 4"

CATTLE GUARD

attle guard

Sanderson et al (1990)