|This series of six articles was written by
consultants working in the forest industry. We are
grateful to them for sharing their expertise ...WVU-ES
KEVIN BELT, R.F., Consulting Forester
Note: This is the second in a series of forestry-related articles to promote proper forestry practices, forestry education, and forestry extension. The series will also speak to some of the misconceptions about forestry.
Forestry activities, particularly harvesting, can have serious consequences on soil and water quality. Any good forester is concerned about these impacts. Measures can be taken to preserve soil and water quality and to prevent their undue mixing.
These measures are known as Best Management Practices or BMPs.
Any activities that involve heavy machinery on mountainous or rolling terrain require cutting roads. Skid roads are used to move logs from stump to log desk by bulldozers and skidders (specially adapted, articulated four-wheel drive tractors). Haul roads are used to move logs from the log deck to the public road. When the roads are built, bare mineral soil is exposed. When soil is exposed, soil or sediment can be moved by the force of water. When sediment moves, it moves toward a stream. The purpose of implementing Best Management Practices is to minimize soil movement, particularly movement into a stream.
Good planning is the best tool in the implementation of BMPs. A logger or forester should look at the big picture of the entire timber harvest area before road construction begins. Proper planning and scouting (walking over the harvest area) will provide information about potential trouble areas. It will determine the best location and design for roads, the slope of roads, and the approach to stream crossings. A good plan will avoid duplication efforts, overly steep road designs, and improper combinations of road, slope, and water. Although improving water quality and providing dry, well-designed roads, a good plan will be more work and expense up front, but overall can make the job easier, more efficient, and more accessible to the logger in the long run.
Activities in streamside areas have the greatest potential for stream sedimentation. In a timber sale contract or in the field, a forester can designate a buffer zone or streamside management zone. Normally, the buffer zone is 50 feet on either side of any perennial branch or stream. Larger creeks and rivers often get buffer zones of ±100 feet. Within these buffer zones, roads may not be located parallel to the stream but may cross perpendicularly-then roads must immediately exit the buffer zone. Furthermore, an adequate culvert or other appropriate improvement must be placed at the stream crossing to keep skidder tires and logs out of the stream flow. Keeping roads and machinery out of streams and streamsides, and placing culverts at stream crossings are by far the most important practices in preventing direct sedimentation of streams. Anything less is unacceptable.
Furthermore, about half the trees in a buffer zone should be left standing regardless of what cutting method is used elsewhere on the harvest area. These trees are left to provide shade for the stream to prevent water temperature changes.
In rolling or mountainous terrain skid roads must be sloped to overcome elevation changes. When a sloping skid road is built, however, it provides a potential pathway for bare soil to travel via rainfall and runoff. This can be mitigated by means of a water-bar. A water-bar looks like a two- to three-foot high, diagonal speed bump built of dirt on a skid road. The downhill side of a water-bar is completely open for thorough drainage. Its purpose is to turn running water off the sloped bare soil of the road and onto the forest soil where the vegetation root mass and humus can more easily soak up or disperse the water flow. Regardless of whether the timber has been cut and regardless of the extent of the cut, this root mass is nature's perfect sponge for rainfall and runoff.
Water-bars must be located at regular intervals to break the flow of water. These intervals are closer when the road is steep; the intervals are farther apart on less steep roads. For instance, if a road rolls at a 5% grade, then water-bars should be built every ±135 feet; if a road has a 10% grade, then water-bars should be built every ±80 feet; if a road pitches up at a 25% slope, then water-bars should be built every ±50 feet. If possible, roads should not be built at a slope greater than 30% grade. By no means should a road be built straight up the slope or where there is no possibility for proper drainage.
Well-built and properly placed water-bars are 99% of good reclamation work. There is little chance for sediment movement when water-bars are well constructed. When this practice is combined with proper streamside management, a good logger offers little opportunity for sediment to reach a stream.
Log landings are normally the largest area laid bare by heavy machinery traffic. Landings should be located away from running streams. Landing runoff and drainage should be carefully managed. The same rules for Streamside Management Zones enter into the decision for landing location. Though proper drainage is most important, sowing grass on a landing and the nearby skid roads after use is an excellent final touch-and fine advertising for the logger.
Haul roads have yet another set of water management guidelines. Broad-based dips, rolling dips, water turnouts, and outslopes are used to provide drainage on less steep roads. A properly built haul road can actually be a considerable improvement to a property.
These are some of the more basic Best Management Practices for use in rolling or mountainous land. There are many more general guidelines, and even more guidelines for special situations, e.g., wildlife seeding mixtures, silt fences, mulching, fertilizing, and liming. When land is flat or swampy, an entirely different set of BMPs for wetlands applies. If you are considering some type of harvesting activity, contact a forester to determine the Best Management Practices that apply to your particular tract of land.
If you wish to locate a consulting forester, contact the USDA or extension office nearest you.