Repair and maintenance of forest roads
The working life of a forest road has important practical and economic consequences.
All forest roads will experience wear and tear during harvesting operations and it is important to repair them as quickly as possible. Equally the maintenance of a road between harvesting operations will protect the road and minimize environmental impact.
However it is important to distinguish between road repair and maintenance:
Road repair is concerned with the reinstatement of road facilities to a former satisfactory condition. This work is normally required during or following harvesting operations. Heavy machine traffic and timber haulage are the main cause of road damage. The condition of the road before harvesting operations will greatly influence the incidence and severity of subsequent damage.
Road maintenance is concerned with keeping roads not currently in use in a usable condition. Maintenance works are best carried out during the summer months and should be ongoing with particular attention to the maintenance of drains and culverts. Satisfactory maintenance/repair is usually achieved by retaining the standard of the road as built.
Main elements to repair and maintenance
Drainage. The condition of the soil beneath the road will largely determine the strength of the road. Effective drainage in the vicinity of the road by having a clear drain is imperative to ensure that the water table is as low as possible. The cleaning and/or re-profiling of roadside drains must be carried out during dry weather to minimize potential environmental impacts from erosion and sedimentation. The 15 metres tree clearance width required when building a forest road is intended to minimize the shading effect from the trees as they grow and the impact on road drainage. During reforestation it is important that ground preparation operations do not interfere with the existing roadside drainage. A saturated road has less than half the strength of a dry road!
Surface. Road carriageways are usually the most expensive element of forest road construction and therefore good maintenance of the surface is very important. The most common repair and maintenance issues on road carriageways are:
- Potholes. The presence of potholes, more commonly found on flat sections of road, is not a particularly damaging condition in terms of the preservation of the road other than the actual loss of surfacing material. However, heavy potholing does result in an increased and unacceptable risk to the safety of the user and potential damage to vehicles. Potholes are repaired by re-grading and only in exceptional circumstances should it be necessary to re-grade a road more than once a year.
- Camber. An adequate camber ensures that rainfall quickly drains from the road surface into a roadside drain. A poor camber can result in severe erosion of the road surface. Good camber is achieved by re-grading ideally in tandem with repair of potholes and/or removal of vegetation. During re-grading care must be taken to ensure that the graded material does not enter side drains or block roadside edges. After re-grading it is necessary to compact the road surface to prevent the infiltration of water and to provide strength.
- Vegetation. Through lack of use a forest road is likely to become overgrown and in time this can undermine its usage through erosion and loss of strength. How this is remedied depends on the planned road usage. Forest roads serving as main routes for major forest blocks will justify control of vegetation through re-grading and compaction every 3 to 5 years. On roads serving a single forest with harvesting operations every c.4-5 years chemical vegetation control may be a more cost-effective approach.
Pavement thickness. The original constructed road pavement thickness must be preserved otherwise excessive rutting will occur with potentially serious collapse requiring a total and expensive reconstruction. Loss of pavement thickness is most commonly caused by heavy rain, increased traffic, traffic speed and usage by harvesting traffic. Where loss of pavement thickness occurs, re-metalling of the road may be required with crushed stone or approved aggregates only being used. Compaction of the material being spread is important to prevent dispersal by vehicular traffic. Travelling on a forest road by harvesting traffic i.e. processors and forwarders should be avoided.
Other factors affecting the condition of a forest road:
- Winter conditions. Roads that are thawing following heavy frost or covered with snow can be damaged by heavy vehicles. This should be avoided.
- Overloading. The various Road Traffic Acts prescribe the legal loads with which all vehicles must comply. Forest roads are designed to carry the same loads as public roads but the effect of use by excessive loads is probably more evident on forest roads. The cost of repairing damage caused by overloading can be substantial.
Regular inspection of roads during harvesting and periodic inspection at other times, e.g. after storms etc. is necessary to identify problems and plan remedial action.