Trunk_Installation_Guide.pdf

Combahee River Style

Rice Field Trunk Installation Manual

Bear Island Wildlife Management Area South Carolina Department of Natural Resources

Introduction

The best made trunk will not function properly unless installed carefully and precisely. In addition bulkheads must be constructed on either end to hold the trunk securely in place and to prevent the dike from eroding into the water. The required time and effort, while considerable, pays great dividends for years to come.

While each trunk installation varies somewhat with conditions, the information in this manual will allow managers to successfully install a trunk in most situations.

Combahee River Style

Rice Field Trunk Installation Manual

Rice field trunks allow water to pass beneath dikes to control water levels in impoundments managed to provide winter habitat for migrating waterfowl.

Preparation of this manual was funded by NOAA Grant NA03NOS4190168, Restoration of coastal impoundments in the ACE Basin.

Text and photography - Pete Laurie Design and Layout - Karen Swanson

September 2007

Preparation of Site

In some cases a replacement trunk works best in the ex-act location of the old trunk. Often, though, installing the new trunk 40 or 50 feet away requires less time and effort. Either way, water in and out must be dammed off during installation.

Once the new trunk becomes fully functional the old trunk can be sealed off and abandoned in place.

First determine the depth of the existing trunk using a surveyor’s transit. If the old trunk works well at its existing depth then the new trunk should also work at that depth. The bottom of the trunk should be at mean low tide in most loca-tions.

The track hoe operator can then remove the old trunk or dig a new passage across the dike to fit the new trunk. During excavation check the bottom of the hole periodically to achieve the correct depth over the entire length. Dig the hole exactly perpendicular to the dike so that the roadway can cross the trunk in a straight line. The hole should be stepped down on each side to allow for access and to prevent dangerous cave ins.

The hole for the new trunk should be exactly perpendicular to the dike, and the center point of the dike flagged on both sides. Also flag the center of the trunk so that it can line up as close as possible to the center of the dike. The sides of the hole should be stepped down to allow workers easier access to the hole and prevent cave-ins.

A surveyor’s transit or a laser level helps the track hoe operator dig the hole to the exact correct depth.

As the hole nears completion, all parts of it should be checked and re-checked to get the depth uniform, allowing the trunk to sit level.

Setting the Trunk

With a track hoe or crane place the trunk into the hole, taking care to align the flagging with the stakes. Double check to make sure the depth is correct. Then place enough dirt on the center of the trunk to hold it in place during bulk-head construction.

Once the hole is completed, the trunk can be swung into place using the track hoe boom. The spillway should be on the inside, or pond side, of the dike.

Preparation of Trunk

Remove doors and uprights prior to installation. Mark the center of the trunk with flagging. Likewise, mark the posi-tion off the sheeting for the bulkhead based on the width of the dike. Generally, the sheeting should be about 18 inches inside the spillway box on the pond end and the same dis-tance inside the uprights on the tidal end. Temporary stakes on the edge of the hole allow the operator to position the new trunk by lining up the flagging on the trunks and the stakes.

The trunk must be lowered carefully into the hole, making sure it is aligned properly with the dike. A four foot level will allow work-ers to ensure the new trunk is level in both directions.

With the trunk in place, enough dirt should be placed in the center section to hold it securely.

Note the stepped down sides to the hole.

Tack down to the trunk decking two 3x10 boards, leaving a 3-in. gap between them. The gap should be about 18 in.

behind the muzzle. Through this gap drive 3x10 “sloppy V” boards for the sheeting. The first sheeting on either side must fit tightly to the side of the trunk.

With a specially designed board puller and a come-a-long pull each piece of sheeting tightly to the previous piece making a solid wall. Generally, at least 10 sheeting boards should be driven on each side of the trunk. When the sheet-ing is completed, remove the two 3x10 boards and use them for cribbing.

Building the Bulkheads

The bulkheads generally are the same at each end, but dike erosion and soil type may require bulkheads of slightly different style or size.

Sheeting consists of 3x10 treated sloppy V planks. These should be 16 feet in length if the substrate is soft enough to allow them to be driven fully into the mud. Normally, at least eight should be driven on each side of the trunk box.

After determining the distance (usually 16 inches) back from the spillway, or, on the outside end, from the uprights, tack two of the 16-ft. cribbing boards across the trunk with just enough gap between them to slip the sheeting through.

With the bucket on the track hoe, and two workers on the trunk, stand the first sheeting board in place making sure the inside edge is flush with the trunk upright. Drive the board until about 65 inches remains above the top of the trunk box. Sheeting can later be trimmed off even with a chainsaw if necessary.

Then move to the other side of the box and drive the first sheeting on that side. Continue driving sheeting on that side, us-ing a board puller, a chain and a come-a-long to pull against the first sheeting on the opposite side. This insures that the sloppy V joint fit together tightly.

Once the necessary num-ber of sheeting boards has been driven on that side, switch back to the first side and using the same method, drive those remaining boards. The tacked down crib-bing boards can then be removed.

Cribbing

Cribbing consists of 16-24-ft. treated 3x10’s stacked on edge against the inside surface of the sheeting. Start with 16-ft. pieces on the bottom and complete with two or more 24-ft. pieces at the top to reduce dike ero-sion. Place enough dirt behind the cribbing to hold the boards in place.

The sheeting is backed with horizontal crib-bing boards, usually 3x10’s. Start with 16-ft.

boards on the bottom and finish with 20-ft.

or 24-ft. boards at the top as the hole gets wider. The cribbing boards are held in place by fill dirt.

Poles

After completing the sheeting and cribbing on each end of the trunk, place a 25-ft treated pole horizontally in front of the sheeting 2-3 feet above the top of the decking on the trunk. This may require removing extra substrate on each side of the trunk to accommodate the length of the pole.

With the horizontal pole in place, drive two 25-ft. poles, one to either side of the trunk, into the substrate making sure they are snug against the outside of the horizontal pole. Repeat the process on the other end of the trunk.

Drill holes through the cribbing and sheeting so that ¾-inch stainless cable can be run through the holes and around the vertical poles. With the cables in place, clamp the ends securely together so that they tie the two bulkheads as tightly as possible into one unit. The hole can now be completed back filled to rec-reate the original dike and road bed.

With the sheeting and cribbing finished, place a “lay down log” approximately 25 feet in length so that it is centered on the trunk and level. The ends of the log rest on the sides of the hole. The log should be about 36 inches above the top of the trunk.

Drive 25-ft poles, two to each side of the trunk as far into the mud as possi-ble. The first pole should be adjacent to the trunk and the other one about 45 inches to the outside. Drive the poles as straight as possible and tight against the lay down log.

Finally, drill holes through the cribbing and sheeting on both ends. Run 5/8-in.

stainless cables through the holes and tie the four poles and lay down logs and either end together across the top of the dike. The bulkhead is now se-cure and can be back filled to replace the original dike.

Apron

An apron installed on the outfall end of the trunk will greatly reduce erosion which can undermine the trunk and cause the end to settle. Aprons should be about 16 feet by 10 feet with 3x10’s stood on edge on each side to form a shallow trough.

Start with two 4x8’s placed about six feet apart, then nail 3x10 sloppy V’s (about 11 each) to the 4x8’s which should extend about 12 inches to either side. With the trunk in place, lower the apron into the creek and slide one end under the trunk muzzle about two feet. Drive stakes into the mud and nail them to the 4x8 extensions on either side.

To reduce erosion on the outside, or river side, of the trunk install an apron approximately 16 feet long and 11 feet wide. Build the apron with 3-in. slop-py V. Using the track hoe, carefully slide the end of the apron under the muzzle of the trunk.

Secure the apron with four 4x8-in boards driven into the mud, nailed to the sides of the apron and cut off flush with the sides.

Conclusion

Replace the uprights and re-hang the doors. The ends of the trunk can then be opened up by removing the temporary coffer dams allowing water to flow freely through the trunk.

A completed trunk installation showing the bulkhead and the replaced dike.

A completed trunk installation with a walkway added. Walkways make it easier to adjust the doors and pull or replace spillway boards.

The South Carolina Department of Natural Resources, an Equal Opportunity Employer, prohibits discrimination on the basis of race, color, gender, national origin, disability, religion or age. Direct inquiries to the Office of Human Resources, PO Box 167, Columbia, SC 29202.

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Printed on Recycled Paper September 2007