Appropriate design of roads and stream crossings

Forest access roads and other roads in rural areas often cross streams and other small watercourses. The design and material used in forest road building may have strong impact on erosion risk and water quality in streams. Bridges or culverts used at stream crossings must be properly designed to minimise negative impacts on the aquatic environment. Poorly designed or poorly constructed stream crossings can lead to increased sediment mobilisation, changes in flow patterns and even flooding upstream if insufficient water is transported. Such flooding can also wash out bridges or stream crossings resulting in costly repairs for the road owner and sediment pollution downstream. Increased sediment mobilisation results in loss of aquatic habitat threatening species such as freshwater pearl mussels and eliminating spawning grounds. To mitigate these impacts, effective practices include minimising road surface runoff and overland flow velocity, which reduces the energy available to detach and transport soil particles to streams. Limiting disturbance in logging areas and reducing connectivity between forest roads, skid trails and streams are important measures to control sediment movement.

Bioengineering designs tailored to specific areas can further support soil stabilisation. From a construction perspective, reducing excavation depths, using technologies to limit soil compaction, and ensuring efficient road network designs - avoiding hydrologically active zero-order basins - are critical. Techniques such as sloping road embankments, immediate revegetation and minimisation of skid trails contribute to long-term stability.