Introduction

The installation of a stream crossing as a conservation practice can improve connectivity on a farm by providing long-term stable access for people, livestock, farm equipment, and vehicles. Properly designed and installed crossings help reduce soil erosion and improve water quality by decreasing sediment and animal waste loading into streams. The types of stream crossings covered in this guide include rock ford crossings, geocell ford crossings, concrete ford crossings, and culvert crossings.

Much of the information discussed within also applies to watering ramps. Watering ramps are similar in design and structure to ford stream crossings except that they only span one side of a waterbody. Rock Ford Crossing Ramps can provide stable and improved access for livestock watering on creeks or ponds, while also improving water quality.

This document is designed specifically to assist landowners interested in self-installation of stream crossings and watering ramps. It utilizes easy-to-follow photographs and diagrams to highlight common installation techniques as well as specific requirements for those who are participating in one of the Natural Resources Conservation Services’ (NRCS) Farm Bill programs. This guide is not intended as a substitution for the more detailed NRCS Construction Specifications document, which should also be reviewed during project planning (http://efotg.sc.egov.usda.gov/treemenuFS.aspx).

Planning

NRCS is available to provide technical assistance to landowners in planning and installing stream crossings. Assistance regularly includes: site selection, design, specifications, recommended materials Culvert Crossing and quantities, pre-construction meetings, daily inspections, and final inspections. Financial assistance is also available through NRCS on a competitive basis. NRCS may also recommend or require other best management practices to accompany stream crossings in order to protect other natural resources.

There are many factors to consider when determining the design and location of the stream crossing. The design of the crossing should be determined by NRCS staff (rock ford, geocell ford, concrete ford, or culvert pipe), and will be based on local site conditions. Concerning location, the ideal crossing should be installed perpendicular to the direction of the stream flow. They should be located in areas where streambeds are stable, and where erosion and flooding impacts can be minimized. Areas to avoid include: abrupt changes in channel slope, Watering Ramp turbulent water or overfalls, confluences with tributaries, wetland areas, shady areas in the stream buffer, or where bridges and culverts are immediately upstream. All installed crossings should still provide normal passage of water, fish, and other animals during all seasons.

Stream Crossing Installation Guide – Page 1 of 4

Ford Crossings

The width of a ford crossing will depend on the intended use. Livestock crossings must be at least six feet wide and multi-use crossing should be between 10 and 20 feet wide (See Figure 1). The length of the crossing should span over the entire natural channel. The final surface in the bottom of the stream shall be the same elevation or slightly lower than the original stream bottom to allow for natural stream flow.

Approaches should be stable and blend with existing site conditions where possible. They should not exceed a gradual 5:1 slope. All surface runoff should be diverted around the approaches. Side slopes next to stream crossings should be no steeper than a 2:1 slope and be stabilized with vegetation, geotextile, rock, or a combination of material.

Site preparation. Once you have decided on a location for the specific type of ford Preparing HUA Site crossing, you can prepare the site. The clearing and grubbing should be kept to a minimum to prevent erosion. The foundation should be cleared of all trees, brush, stumps, roots, sod, and other debris. All waste materials should be deposited in a designated area outside the natural flood zone.

Foundation Excavation. Excavation should be accomplished to the depths, widths, and lengths required by the design. Depending on width of stream, excavation may be limited to one side of the stream at a time in order to divert the stream using a pipe or ditch. The stream may also be temporarily impounded during construction, but care should be taken to minimize erosion and sedimentation.

Trenches for anchoring geotextile fabrics should be excavated along the ends of both approaches (terminal anchors), as well as along the length of both sides of the crossing (side anchors). Dimensions of the trenches should be at least 12 inches deep by six inches wide. Figure 2 (below) displays the locations that may be recommended for geotextile anchor trenches.

Geotextile Fabric Installation. Geotextile fabric meeting the minimum requirements (see construction specifications) is recommended for installation on the entire crossing surface area. The fabric should be placed in each trench and the trench should be filled with rock to anchor it in place. The proper folding of the fabric during trenching, as well as the overlapping of separate fabric rolls, are required to ensure that the stream flows cannot uproot a fabric edge. This is more important for the side anchors than the terminal anchors. The method used to lay fabric length(s) on side trenches can vary depending on whether you are using one separate length of fabric (Figure 3) or multiple lengths of fabric that need to be overlapped (Figure 4).

Stream Crossing Installation Guide – Page 2 of 4

Whenever fabric is being laid back over a backfilled trench, it must extend at least six inches beyond the trench. When two or more separate fabric layers are used, they must overlap each other by at least 18 inches. When overlapping these fabric sheets, make sure the top sheet runs in the same direction as the stream flow (See Figures 3 and 4). Construction equipment should never be operated directly on the geotextile surface.

Anchoring pins should be of sufficient size to hold geotextile until the crossing has "hardened" after construction. Commercially available anchoring pins or large nails may not be large enough to hold the geotextile. Sharpened, fabricated pins using No. 3 reinforcing steel or material of equivalent size and durability have often been effective. Anchoring pins should be placed at three foot centers through the fabric at: all excavated trenches, all overlapped fabric sheets, and across the width of the channel.

Surface Materials.

For rock ford crossings, after the geotextile material is anchored and pinned it should be covered with at least six inches of appropriately- sized rock. If larger rock sizes are required due to the flows of the stream, it may require a layer of smaller surfacing stone to fill voids and create a more uniform surface layer. Crossings specifically for livestock may require a two-to- four inch hoof contact zone made of Graded Aggregate Base (GAB) over the surfacing stone (See Figure 5).

For geocell crossings, the geocell mats must be installed according to manufacturer's recommendations. This includes installing the mats on a geotextile-lined excavated surface (six inches deep). Generally, the geocell mats will be filled with GA-DOT No.4 coarse aggregate and then overfilled by at least two inches when thoroughly compacted.

Concrete crossings should have a minimum compressive strength of 3,000 psi at 28 days. Concrete ford crossings need a minimum thickness of five inches with minimum reinforcement of six-inch by six-inch, six-gauge welded wire fabric. The concrete slab should be poured on a four-inch thick rock base, unless the foundation is otherwise acceptable. Toe trenches (6-inches wide x 18-inches deep) are also used for concrete crossings, although they only extend halfway up the approaches.

Stream Crossing Installation Guide – Page 3 of 4

Culvert Crossings

Assistance with culvert pipe calculations and designs are available through NRCS. The pipe’s diameter should be sized to handle at a minimum the bankfull flow, and the pipe’s length of the culvert should extend the width of the crossing including the side slopes. It is highly recommended that the culvert pipe be placed on or below grade with the existing stream bottom to accommodate passage of aquatic species. Acceptable culvert materials include concrete, corrugated metal, corrugated plastic, or high quality steel.

Culverts should be placed on a firm foundation, but should not be laid directly on rock; there must be a soil bed or gravel cushion of at least six inches between the pipe and rock (Figure 6). Joints of pipe need to be sealed in accordance with the manufacturer’s specifications. The outlet end of culverts should terminate on natural rock streambeds or a designed protective outlet structure.

Backfill should be placed around the pipes and thoroughly compacted every nine inches. The recommended fill depth on top of the culvert pipe is equal to one-half the diameter of the culvert (no less than 24 inches). The fill should be built up over the culvert such that any stream overflow will cross the road at a point away from the culvert to protect the structure from erosion. The top of the compacted fill should be covered with geotextile fabric, and then with six inches of GAB. Riprap or a concrete headwall may be needed on the side slopes to prevent erosion.

Watering Ramps

Watering Ramps are identical in design to a stream crossing, except that they are only located on one side of the waterbody. These ramps serve as a conservation practice because they limit cattle access to surface waters to a designated location instead of giving them full access. Similar to crossings, ramps can be constructed of rock, concrete, or geocell. Care should be taken to ensure that all excavation, trenching, fabric placement, and layering of surface materials follow the same guidelines as described above.

Operation, Maintenance, and Other Considerations

Before disturbing any land near a stream, investigate if permits should be obtained from the State, the U.S. Fish and Wildlife Service, and the Army Corps of Engineers. After construction is completed, it is recommended that all disturbed areas should be vegetated as soon as practical. Each side of the crossing should be fenced so that cattle will be restricted to the protective crossing surface. Electrified hanging chains along the crossing have proven an effective way to keep livestock from escaping by traveling upstream or downstream. Ford crossings with free access by cattle should have minimal shade to reduce cattle loafing time in the stream.

An operation and maintenance plan should be developed and implemented for the life of the practice. The plan normally recommends inspecting the stream crossing and associated fencing after each major storm event, with repairs made as needed. During high flows, sediment and deposition may occur on approaches to fords. Excessive soil or debris deposition should be removed periodically to maintain proper operation of the stream crossing.

Project Information: Funds for this project were provided by the USDA Natural Resources Conservation Service and administered by the Two Rivers RC&D Council.

Non-Discrimination Statement: The United States Department of Agriculture (USDA) is an equal opportunity provider and employer.

Stream Crossing Installation Guide – Page 4 of 4