How our forests develop is based on more than the types of trees we plant – environmental factors such as soil type and depth, rainwater infiltration, and elevation also play an important role. Protecting these factors and their ecological processes is a critical part of forest road planning and maintenance. Well-maintained roads also help ensure sedimentation does not reach important water systems within a riparian zone.
Riparian zones are the ecological link between terrestrial and aquatic systems. In addition to containing some of the more productive conditions for growing timber, they are heavily used by wildlife, provide essential habitat for fish and wildlife, and are key to protecting water quality. When they are properly stewarded they stabilize banks and filter sediment, as well as provide nutrients, large woody debris, and shade that fish and wildlife depend on.
Well-maintained riparian zones have deeper soils that hold moisture longer into the summer and saturate earlier in the fall, which allows the road surface and subgrade to hold moisture for a longer period of time. The subgrade and road surface moisture is also increased by the need to meet rule designated shade requirements within the riparian management zone (RMZ). By keeping a canopy of needles and leaves above a road, the sunlight and air movement is reduced during the fall and late spring. Needles and leaves create a mat that seals in moisture, both of which prevent the road surface from drying out. Using roads during the wet season causes the binding friction of surface rock to deteriorate and allows for the movement of fine soils from the subgrade to “pump up” through the margins between the pieces of gravel. This fine sediment stays suspended in surface runoff and can be carried into the ditches and streams affecting water quality and fish habitat. Generally, reducing sediment impacts in RMZ’s requires more cross drains, ditches on both sides of the road, sediment traps made from fiber or rock, and increased maintenance to keep them functional.
The forest practices rules discourage the construction of new roads within an RMZ:
“Except for crossings, new stream-adjacent parallel roads shall not be located within natural drainage channels, channel migration zones, sensitive sites, equipment limitation zones, and riparian management zones when there would be substantial loss or damage to fish or wildlife habitat unless the department has determined that other alternatives will cause greater damage to public resources. Proposals with new stream-adjacent parallel roads will require an on-site review by an interdisciplinary team WAC 222-24-020 (2).”
So how do you protect ecological functions while maintaining roads within a RMZ’s? By:
- Locating new roads outside of natural drainage channels, channel migration zones, sensitive sites, and equipment limitation zones. Exceptions may be allowed after an on-site review by an interdisciplinary team.
- Conducting road maintenance in riparian areas during the dry season.
- Completing ditch cleaning re-vegetation with grasses or clovers to reduce sediment and bare soils.
- Making sure culverts are functional and catch basin and outfalls are rocked to prevent scouring.
- Constructing drivable dips in the road grade above culverts to allow water to move across the road if the culvert becomes over topped with water.
- Discontinuing hauling immediately if a road begins to introduce fine sediments into the water, causing discoloration of the streams.
- Adding, cleaning and repairing sediment traps.
- Limiting access during seasonal wet periods and the wet season.
- Decommissioning or abandoning roads in riparian zones by reforesting and seeding the foot print of the road with grass or clover, and removing all cross drain/relief culverts.
Remember that good roads protect water quality and riparian habitat, and prevent damage to public resources by:
- Providing passage for fish during all life stages.
- Preventing mass wasting.
- Limiting delivery of sediment and surface runoff to water.
- Avoiding the capture and redirection of surface or groundwater. This includes retaining streams in their natural drainages and routing subsurface flow captured by roads and road ditches back onto the forest floor.
- Diverting most road runoff to the forest floor.
- Designing water crossing structures to the 100-year flood level to provide for the passage of bedload and some woody debris.
- Protecting stream bank stability, the existing stream channel, and riparian vegetation.
- Assuring no-net-loss of wetland function or fish habitat.
Looking at roads as part of the ecological forest function protects your investment, ensures the protection of important fish and wildlife habitat and maintains good clean water quality.
Next Newsletter: Are Your Roads Ready for Fall?
By Boyd Norton, Northwest Washington Landowner Assistance Forester, DNR