Chapter 9: Forest Resource Road and Crossing Erosion and Sediment Management
Forest resource roads and crossings are sources of sediment. This chapter provides general guidance for considerations for forest resource road erosion and sediment management for those involved with Forest Service Roads.
Roads and associated crossings should be located, designed, constructed, inspected, maintained, and deactivated recognizing that they are sources of sediment that can detrimentally impact upon other forest resources such as water quality, fish streams and fish habitat.
Consideration for management of sediment should be made through the life-cycle phases of forest resource roads and crossings. Each phase impacts sediment development and mobilization. It is more effective and efficient to integrate sediment management in road activities than to deal with it in a reactive manner. Plan all activities to minimize the potential for sediment development and movement.
Some factors to consider in all road and crossing phases for sediment development and management:
- Fine texture, non-cohesive soils are more erodible and mobile than coarse soils
- Minimize exposed soil area and exposure time
- Minimize exposure to wind, rain and runoff
- Maintain natural drainage patterns and dispersion to avoid accumulation and redirection of runoff onto exposed soils
- Minimize soil disturbance to minimize sediment generation
- Machine methods to minimize disturbance
- Re-vegetation disturbed slopes as early as possible to limit sediment generation and transport
- Rough surfaces generally limit sediment generation and transport more than smooth
- Avoid high erosion potential soils and sites
- Avoid sediment mobilization and delivery to sensitive sites (eg water courses)
- Avoid activities in close proximity to watercourses and sensitive sites
- Connectivity of sediment sources to water courses via run off, ditches, culvert discharges, etc.
The following provides considerations for sediment management for the life cycle phases of forest resource roads and crossings. Implementation of suggested practices will depend on site specific situations.
Plan and design forest road locations and geometry to minimize sediment development and exposure and to avoid direct delivery of sediment from roads into watercourses or sensitive habitat areas. Plan and design runoff drainage systems to filter through stable forested, vegetated areas and not directly into water courses. Locate roads and crossings to avoid sensitive slopes and soils, to minimize cut and fill exposed soil slope areas. Locate roads away from water courses and that have vegetation buffers. Identify riparian areas and incorporate measures in design to minimize opportunities for sediment generation and mobilization. Locate borrow/waste sites to minimize sediment delivery to watercourses and to avoid disturbing sensitive slopes and soils.
Design and construct the forest road prism with appropriate subgrade and surfacing materials that meet the expected design life, loading, seasonality, and traffic volume and with consideration for sediment management.
Consider the subgrade and surfacing materials when planning and constructing the forest road prism. Along with the expected design life, loading, seasonality, and traffic volume, consideration should also be given to sediment management. Consider integration of rolling grades, dips and swales, into designs to limit long sections of road surface that will accumulate and redirect water drain water from the road surface. Where such features are implemented in the field, document and consider marking them such that maintainers are aware of the features and do not compromise them.
Management of road drainage is key to minimizing erosion and sediment development. Design roads with adequate drainage to maintain natural drainage patterns and natural dispersion of runoff. Avoid accumulating and concentrating flows which will have greater erosive capacity. Design stream crossings such that runoff drains away from the water course, and they are not at low vertical road points which results in runoff with sediment discharging directly into the stream. Design for road runoff and ditches to not be connected and directly discharge into streams.
Plan and implement construction practices that minimize soils movement, exposure of disturbed soils, time frame for disturbed soil exposure, and generation of mobilized sediment. Avoid construction works during wet weather. Install temporary erosion control measures to limit transport of sediment to water courses and sensitive habitat. Maintain existing surface vegetation where possible. Protect exposed soils with erosion control measures and establish vegetation as early as possible. Around spoil sites and new crossings use erosion control blankets or straw to reduce the impact of rain drops and aid in the establishment of vegetation. Avoid equipment stream crossings within wetted perimeters and where required provide measures for clean equipment crossings. Install drainage structures concurrent with subgrade construction.
Shape road surfaces to shed water – crown, inslope or outslope the road surface as may be suitable and appropriate to the site conditions.
Remove or breach roadside berms which would retain and accumulate water on the road surface, unless the berm has been constructed for a specific purpose.
Install mechanical methods to reduce the velocity of the water in the ditches (ie. sumps or sediment ponds) to encourage sediment settlement and capture.
Identification of erosion and sediment potential for delivery to water courses or sensitive habitats is a key focus of road inspections. Even with careful planning and design, things can change particularly from upslope activities. Planned routine road condition inspections is intended to identify problems and address them with maintenance, such that they are appropriate managed to minimize impacts.
Procedures can be implemented where observations by other forest resource practitioners of problems on roads, including sediment getting into streams, lakes and wetlands are reported to those responsible for maintenance.
Careful examination of the drainage of the road, culverts, ditches and crossings should be undertaken as surface runoff can severely impact erosion and sediment development. Opportunities for runoff accumulation, concentration and diversion should be identified for remediation. Road runoff drainage and dispersion should be consistent with natural drainage patterns. The road surface should shed water and not transport it any appreciable distance. Any grader berms or windrows will retain, accumulate, and concentrate surface runoff and should be identified for addressing unless they have been established for an intended purpose such as retaining runoff from discharging onto sensitive sites.
Consider utilizing the Forest & Range Evaluation Program (FREP) Water Quality Monitoring, Water Quality Effectiveness Evaluation Protocol, which provides an estimation of volume of fine sediment generation and its potential impact on nearby water quality and fish habitat. The evaluation assesses a sites connectivity to nearby water sources, the contributing factors for fine sediment generation, and allows for the prioritization of sites from Very Low to Very High potential impact to water quality. The evaluation also provides remediation options to reduce fine sediment generation.
Plugged or non-functional culverts, ditch blocks, erosion sites that disrupt the functionality of the road drainage system and are sources of sediment should be identified for remediation.
At crossings, inspect for road runoff being directed to the crossing and opportunities to redirect and disperse through the forest floor. Examine for potential for sediment generation and mitigation opportunities within the stream channel.
Road sections or appurtenances where runoff drainage carries sediment directly into water courses should be identified for remediation.
Unstable and exposed cut or fill slopes contributing to sediment development and delivery to water courses or sensitive sites should be identified for revegetation and or remediation.
Maintenance to address sediment delivery or potential sediment delivery to water courses can be determined during and after identification of problems from road inspection.
As discussed previously, road runoff and drainage management are key means to address sediment development and delivery to watercourses or sensitive habitat. Maintaining natural drainage patterns and dispersion of runoff from roads, road surfaces and crossings is key.
Training of grader operators and other maintenance personnel on sediment potential and impacts, the influence of their activities, the importance of road drainage and sediment control techniques and practices, will greatly influence outcomes.
Maintenance methods for managing surface water runoff include:
- Grading to crown, outslope or inslope such that road surfaces shed water effectively; ensure that runoff is not discharged onto sensitive slopes or areas
- Remove or breach grader berms which serve to retain and accumulate water on road surfaces
- Adequate and clear road ditches to runoff to suitable points of discharge that provide opportunity for sediment settlement and dispersion, not directly into water courses
- Adequate cross drainage in the form of cross drain culverts and road surface treatments (such as waterbars, cross ditches, vertical road swales) to maintain natural drainage patterns and dispersal of flow, designed to carry water from one side of the road to the other and/or have runoff flow off the road surface
- Functional clear cross drain and streamflow culverts, suitably armoured to minimize erosion; culverts with functional ditch blocks to redirect water from ditches into culverts
- Vegetation of exposed soil cut and fill slopes
Care and consideration for sediment development and potential for delivery to watercourses and sensitive sites during deactivation of roads and stream crossing activities must be taken. Plan and implement deactivation practices that minimize soils movement, exposed disturbed soils, time frame for soils exposed exposure and generation of mobilized sediment. Particular attention to management of surface flows and runoff is required considering post deactivation work access and implications. Maintain and re-establish natural drainage patterns as possible. Revegetate disturbed soils as soon as practicable post disturbance.
More in-depth information relating to resource road erosion and sediment management can be found in the following resources: