2 - Site Selection / Forest Road Drainage Installation Practices in the Pacific Northwest

Forest Road Drainage Installation Practices
in the Pacific Northwest

2 - Site Selection	Safety, Machine Crossings, Construction Timing

Approaches and Safety

Once a crossing has been located (preferably along a straight stream reach with stable banks), fine-tune the horizontal and vertical alignment. If extreme cuts, fills or grades are required to get into and out of a crossing, layout personnel must run accurate gradelines to ensure that horizontal and vertical alignment of drainage structure and road are compatible. Consider visibility, grade breaks, design speed and seasonal restrictions such as icy driving conditions if the road system is to be operational during the winter. In some cases, a road centerline shift of 1 - 2 meters can dramatically improve the alignment, and also work towards a balance between cut and fill volumes. Avoid alluvial fans if possible unless you can cross at or near the apex. Stay away from sites with unstable banks or large cuts, especially in fine-textured soil, and important fish habitat features, i.e., spawning or pool/ debris complexes. Road maintenance and erosion protection at such sites can be a costly and ongoing challenge.

Access and Machine Crossing

Layout personnel must try to balance safety, environmental protection, and cost. Will access to one or both sides be a problem during the installation? Outside the fisheries window, even a "once-only" machine crossing must be approved and can become very costly if the initial risk assessment requires additional measures to reduce environmental risks to acceptable levels. Consider using skid bridges or even placing the bridge structure temporarily for the initial machine crossing, in order to protect streambank and channel stability. Avoid crossings that involve blasting or endhauling for approach work at the far side of the stream, especially if the work requires a temporary bridge as a working platform for machinery.

Construction Timing

Always maintain water quality for fish populations and licensed water users on site or downstream from it. Usually, work outside the wetted perimeter of the stream can be done at any time of the year. Even if there is no risk of sediment generation, or fish are not on site, it is good practice to install drainage structures during low water flows. If water quality or fish presence are an issue, work should occur during preferred fisheries windows applicable to the operation (check with local agency representatives) or utilize specific agency-approved alternative measures for risk reduction such as dewatering channels and fish removal. Effects on water quality often occur from exposure of subgrade during prolonged or intense wet seasons, spring break-up, the failure to install temporary or permanent drainage structures and cross drains concurrent with construction, and poor ditch management. Providing or maintaining drainage is also often overlooked during pioneering and tote road construction, and during right-of-way harvesting activities with feller-bunchers, skidders and forwarders.

2 - Site Selection