6. Route Reconnaissance and Location

Armed with the guides and constraints developed during the land use planning process, the next step is to determine the specific road location. Alternative routes should be carefully reviewed in the office and at the site, utilizing all available background information (soil survey, etc.) and technical expertise. Some important guidelines to help reduce erosional impacts during road location are:

1. Avoid high erosion hazard sites, particularly in areas where mass erosion is a problem. In such areas, slight location changes can often eliminate a major erosion problem.
2. Minimize the area of road disturbance by taking advantage of terrain features such as natural benches, ridgetops, and lower-gradient slopes,
3. If necessary, include short-road segments with steeper gradients (consistent with traffic needs) to avoid problem areas or to take advantage of terrain features.
4. Avoid mid-slope locations on long, steep, unstable slopes, especially where bedrock is highly weathered or soils are plastic.
5. Locate roads on well-drained soils and rock formations that tend to dip into the slope; avoid slide prone areas characterized by seeps, clay beds, concave slopes, hummocky topography, and rock layers that tend to dip parallel to the slope.
6. For timber harvest roads, take advantage of natural log landing area (flatter, better drained, open areas) to reduce soil disturbance associated with log landings and temporary work roads.
7. Avoid undercutting unstable, moisture laden toe slopes when locating roads in or near valley bottoms.
8. Vary road grades where possible to reduce concentrated flow in road drainage ditches and culverts and to reduce erosion on the road surface.
9. Select drainage crossings to minimize channel disturbance during construction and to minimize approach cuts and fills.
10. Locate roads far enough above streams to provide an adequate buffer area or be prepared to catch sediment moving downslope below the road. A number of guides have been developed for establishing width of buffer areas based upon hillslope gradient, parent material, cross drain spacing, and so forth. (such as, references 23, 27). The guide developed by Packer (reference 23) is presented as Table 2.

Table 2.

Protective-strip widths required below the shoulders ¹ of 5-year old ² logging roads built on soil derived from basalt ³, having 9 meter cross-drain spacing ², zero initial obstruction distance ⁵, and 100% fill slope cover density ⁶.

1. For protective-strip widths from centerlines of proposed roads, increase widths by one-half the proposed road width.
2. If storage capacity of obstructions is to be renewed when roads are 3 years old, reduce protective-strip widths 7 meters.
3. If soil is derived from andesite, increase protective-strip widths 30 centimeters; if from glacial silt, increase 1 meters; if from hard sediments, increase 2.4 meters; if from granite, increase 2.5 meters; and if from loess, increase 7 meters.
4. For each 3 meters increase in cross-drain spacing beyond 9 m, increase protective-strip widths 30 centimeters.
5. For each 1.5 m increase in distance to the initial obstruction beyond zero (or the road shoulder,) increase protective-strip widths 1.2 meters.
6. For each 10% decrease in fill slope cover below a density of 100%, increase protective strip-widths 30 centimeters.

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Last Modified: 08/20/2008