Crossing Structures

It is critical that planners, construction managers, and operators work together to develop a construction plan that supports the objectives of habitat protection. Through communication and involvement of all parties, an understanding of the potential impacts and/or mitigation can be promoted. Basic measures for potection, such as avoiding storing materials, fuelling and servicing equipment, undertaking equipment maintenance, and cleaning in reiparian areas, go a long way to reducing impacts. Excavation should be suspended during periods of inclement weather when the potential for damage to the environment is greatest, i.e. heavy, substantial rainfall.

Design and installation

The correct selection and installation of culverts is one step in ensuring tht natural drainage is maintained and sediment transfer is kept to a minimum. There are many choices of culvert materials; wood, concrete, metal and corrugated polythelene.

Wood Culverts

Log culverts can be efficient and durable structures that protect natural stream feastures and can be ideal for forest road construction where suitable logs and experienced crews are available.

Culvert Installation considerations

Proper installation of culverts - regardless of the material used - is critical to ensuring that road stability will not be compromised by ineffectively installed drainage. Unstable or erodable fill at culvert inlets and outlets should be protected with erosion-resistant material to prevent scour and erosion. The foundation beneath the pipe must provide reasonably uniform resistance to the imposed pressures. Avoid installing culverts where situations may cause uneven settling or pressure points on culverts leading to blockage.

Arches

The multiplate arch used for drainage is a semi-circular, galvanized, corrugated steel structure, which does not disturb the stream bed and provides a natural course for water flow. The arch is constructed by bolting single, curved, steel plates together onto prepared footings. Properly designed and installed, the arch has an expected service life of 100+ years with minimal maintenance.

Slash and Debris

Slash and debris must be disposed of and managed in a manner that will ensure that the material does not enter a watercourse or contribute to slope instability.

Subgrade construction

Temporary or permanent drainage systems must be built concurrent with subgrade construction, and must be fully functional and maintained. Excavated material must not be sidecast on steep slopes with high or very high mass-wasting potential.

Backfill materials and compaction

To ensure long service life, culverts must be properly backfilled and compacted. Granular materials such as pit-run gravel or coasre sands are recommended. Ensure that the material does not contain large rocks that could, over time, impact the structure.

Most culvert fill failures are caused by the lack of adequate compaction during backfilling. When cohesive-type materials are used, attention must be given to ensuring it is compacted at optimum moisture content. Thorough compaction should be done in lifts of 150 to 300 mm of material at a time, and worked by hand or with mechanical equipment, tampering rollers, or vibrating compactors.

Bridge and major culvert inspection, evaluation, and maintenance

All temporary and semi-permanent bridges and major culverts must be inspected at least once every two years and permanent bridges at least once every three years, or after unususually high flows and other unexpected events that could damage structures. Records of inspection, noting the general condition of all components, must be kept. Follow-up actions to implement the inspection results are critical to excellent drainage control.

Wood Bridge Structure (cross section)

Road inspection and maintenance

Roads must be inspected an maintained to protect the strutural integrity of the road prism, keep drainage systems functional, and ensure user safety requirements. Maintenance must ensure that sediment production and effects on other resources are minimized. An annual maintenance plan must be prepared and followed. New to the industry is the use of "inspection tracking system." Many operations have hundreds of kilometers of old and new roads; kepping track of all of these can be a formidable task.

Inspections and remedial work must be carried out as often as indicated by the risk to the road, its users and adjacent resources. This inspection process must assess the adequacy of ditches and culverts, the requirements for improved drainage works, road surfacing or revegetation, and other elements of road integrity and safety.


Stream Crossings Directory
Introduction Crossing Structures
Planning Revegetation
Protecting Aquatic Habitat Deactivation
Information for this wall chart was compiled by Eric L. Kay, of  Kay and Associates, Forest Road Consultants and International Training Consultants

This wall chart was produced by Logging and Sawmilling Journal