Best Management Practices
Department of Agriculture
Division of Forestry
Abundant supplies of clean water has long been one of the main benefits derived from Tennessee's forested watersheds. Protecting water quality and preventing soil erosion during forestry operations has become an important responsibility for forest managers, forest landowners and loggers.
Best Management Practices (BMPs) are practical guidelines that can be used to lessen the environmental impact of forest management activities, such as the construction of roads, skid trails and log landings. This BMP handbook was prepared as a reference guide for those who work in the forest, own forest land, or are concerned about forest management practices and their effect on the environment.
Forestry BMPs are designed to be low cost, practical and easily applicable to all forestry operations. This booklet is designed to guide the user through each aspect of BMP installation, from forest road design, construction and maintenance, to special considerations for streamside management, wetlands, timber harvesting and site preparation for the next forest.
Forestry operations are not major contributors to soil erosion and water pollution in Tennessee. However, poor road construction and logging practices can cause unnecessary erosion. Tearing up the topsoil on the forest floor destroys its filtering action and compacting the soil affects surface water absorption. When surface water is allowed to flow into roads and trails, they become man-made streams that increase in speed and volume as they flow downstream. They tear away the soil, destroy roads, overload streams with sediment and damage streambanks.
By far, sediment is considered to be the most significant pollutant produced by forestry practices. Increased sediment in lakes and streams can kill aquatic life, reduce fish populations and affect water for recreational use and human consumption. This type of water pollution is referred to as Nonpoint Source Pollution (NPS), which simply means that it originates from sources not easily tracable to a single point or area, such as a drainage pipe. Other NPS sources include agriculture, surface mining and urban runoff.
Removing shade from streamsides can raise water temperatures which affects fish and other aquatic life. Damage to these streamside forests also affects wildlife which depend on these habitats.
Forested watersheds are capable of absorbing large amounts of rain and snow, as well as providing a protective layer to dissipate the erosive force of rain drops. In forested watersheds, rain is normally absorbed into the soil faster than it can fall, and overland flow occurs only on areas where water infiltration is impaired by heavy compaction and exposed soil. Forests can absorb all but the most extreme rainfall events.
Erosion is the detachment and transport of soil particles, rock, or organic matter. Erosion is dependent upon precipitation, slope, soil type and cover. Where mineral soil is fully protected by litter and humus, virtually no erosion occurs. Only where soil is exposed by roads, skid trails, and log landings does the possibility exist for soil disturbance and transport of sediment into streams. Over ninety-eight percent of all soil erosion occurring on forestland in Tennessee can be traced to these three sources.
In many instances eroded soil and other materials from roads, skid trails and log landings are deposited harmlessly in nearby forested areas where overland flow infiltrates the undisturbed litter layer and enters the soil profile. The impact to stream systems occurs when forest practices are done too close to streams and sediment is deposited directly into waterbodies.
Forest practices are minor contributors to water pollution in Tennessee since:
Harvesting timber, building roads and other forest management activities can have minimal impacts on forested watersheds if conducted according to BMP guidelines.
Forest roads are constructed for moving timber products out of the woods to market, providing access for fire protection and making the forest available for recreation. Forest roads in Tennessee are usually single track roads with turnouts spaced at appropriate distances.
A well located, constructed and maintained system of forest roads will be safer, allow longer operating periods, reduce operating and maintenance costs and save money for the logger and/or landowner in the long run.
Road Construction usually follows a standard pattern of activities from road location, design and layout. Preplanning is the key to minimizing road construction and maintenance problems.
Proper location of forest roads is the most important factor in preventing water pollution caused by forestry operations. For this reason, road location should be carefully planned before construction begins. Topography, boundary lines and economic limits on skidding and hauling timber will dictate the desired location and extent of the road system.
Road construction usually begins with staking control points along the planned road grade, laying out curves and switchbacks, and finally clearing and excavating the road surface. Forest roads are often built by excavating the road surface out of a hillside. A bulldozer starts at the top of the cut slope, excavating and sidecasting material until the desired road width is obtained. Material from cuts is often pushed or "drifted" in front to areas where fill is needed.
An experienced bulldozer operator can do many road construction tasks, including the installation of drainage structures. Ditches, dips, culverts and other structures are normally installed during this time.
Well-designed forest roads with changing road grades, adequate ditches, and crossdrain culverts are important for controlling drainage and ensuring water quality. The goal should be to drain water off the roads as soon as possible within practical and economical limits. The drainage structures selected should be built into the road at the time of construction.
Broad Based Dips are rolling dips which are more suited to roads which receive repeated use. When properly constructed, they require almost no maintenance and allow normal truck speeds with minimal stress to the vehicle. A broad based dip is constructed by building a 3 percent reverse grade into the existing roadbed, with the bottom of the dip outsloped 2 to 3 percent. For maximum self-cleaning, angle the cross drain 10- 25 degrees downslope.
In order to prevent washout, broad based dips should be armored with large crushed rock, gravel, or other suitable stabilizing material. An energy absorber such as riprap or a level spreader should be installed at the outlet of the dip to slow and absorb runoff.
Recommended Spacing for Broad Based Dips Road Grade Distance Between Dips (percent) (feet) 2 300 3 233 4 200 5 180 6 167 7 157 8 150 9 144 10 140 From the formula: Spacing (feet) = 400/slope + 100 Feet
Water Bars are appropriate on temporary roads which carry relatively low volumes of water on roads and skid trails which will be closed following logging operations. Water Bars should be constructed 8-12 inches deep and outsloped 3 percent to assure good water flow and self cleaning action.
Culverts are effective structures used to carry water in drains, small streams, and side ditches to the other side of the road. Culverts are expensive drainage structures but are more appropriate for permanent type roads expected to receive heavier, more frequent traffic.
Install culverts, as needed, at the time of construction to channel water across roads. Pipe culverts are the most commonly used and are effective in draining water on permanent roads.
Culvert grade should be at least 2% more than ditch grade and skewed 30 degrees. To avoid soil erosion, reduce the outlet speed of culvert water by armoring the outlet with a bed of energy dissipators of rocks or debris.
Proper sizing of culverts is essential to providing adequate drainage. To select the proper culvert for a given situation, terrain, soil, vegetation, cover and precipitation must all be considered.
Talbot's Formula yields the waterway area to drain a given area of land for slopes, soils and cover for a maximum of 4 inches of rain per hour.
Steep Slopes Moderate Slopes Gentle Slopes No. Heavy Soils Heavy to Light Soils Agricultural of Moderate Cover Dense Cover Soils & Cover Acres C = 0.80 C = 0.60 C = 0.40 2 0.8 0.6 -.- 4 1.4 1.0 -.- 6 1.9 1.4 0.9 8 2.3 1.7 1.2 10 2.7 2.0 1.4 20 4.6 2.5 2.3 30 6.3 4.8 2.2 40 7.8 5.9 3.9 50 9.3 7.0 4.6 60 10.7 8.0 5.3 70 12.0 9.0 6.0 80 13.3 10.0 6.6 90 14.5 11.0 7.2 100 15.8 11.8 7.8 150 21.2 16.0 10.7
Area of Diameter of Waterway Round Pipe (Square Feet) (Inches) 1.25 15 1.80 18 3.10 24 4.90 30 7.10 36 9.60 42 12.60 48 15.90 54 19.60 60 23.80 66 28.30 72
A Streamside Management Zone (SMZ) is a strip of land adjacent to any water of the state where soils, organic debris and live vegetation are managed to protect water quality from sediment, excessive temperature, logging debris, pesticides, trash and other pollutants.
Although SMZs are recommended primarily for water quality protection, the indirectly provide a variety of other multiple uses for the landowner and society as well. They are:
The SMZ acts as an effective filter and absorptive area for sediment from forestry operations.There are three categories of streams:
Perennial streams contain surface water within a well- defined channel practically year around under normal weather conditions. These streams may be shown as a solid blue line on a topographic map.
Perennial streams require a permanent strip of trees and shrubs to protect banks and flood plains from erosion; to maintain shade, food and cover for aquatic ecosystems; and to maximize control of logging debris, sediment and other pollutants.
Intermittent streams contain water within a well- defined channel only temporarily following a major rainstorm or as long as ground water is abundant. Intermittent streams may be shown as a dashed blue line on topographic maps. Intermittent streams also require protection, but management restrictions don't year. Forest Management can be practiced here as long as soils, trees, and other vegetation are carefully managed to minimize erosion, compaction, rutting and to control deposition of logging debris and other pollutants into the water channel.
Ephemeral or "wet weather" streams flow in a diffuse manner over depressions in the forest floor, not within a well defined channel, not in direct response to a big rainstorm and continue only for a short period after rainfall ceases.
Ephemeral streams or drainages through a property may require some protection because they are the headwaters of the watershed. Even if they don't contain an aquatic ecosystem on site, the activities that occur in an ephemeral drainage have the potential to impact on the water quality and ecological integrity of your neighbor's property down-drainage.
The appropriate width for an SMZ will vary at different sites on the same property. Generally, the steeper the slope and/or more erodible the soil, the wider the SMZ needs to be. Other factors may also dictate wider SMZs than the recommendations for water quality listed here.
A SMZ that extends a minimum of 25 feet or more from the streambank on level ground can perform most of the needed functions. Some landowners may wish to establish and manage wider SMZs to provide for objectives other than just water quality alone, such as key wildlife habitat, a special place for recreational enjoyment and to establish a manageable size stand for the purpose of timber protection. Outside boundaries of the SMZ should be well marked before harvesting timber.
Slope of Land Between Disturbed Recommended SMZ Area and Stream or Other Water Body Width (Percent) (in Feet) 0 25 10 45 20 65 30 85 40 105 50 125 60 145
SMZ planning should be done before the beginning of the timber harvest. Forest management plans, timber sale agreements and site preparation contracts that contain very site specific Best Management Practices (BMPs) can document the landowners, loggers and forester's attempt to minimize adverse environmental impact. Detailed maps, instructions and specifications should be included in the plans.
Because they are potential sources of large amounts of sediment, stream crossings should be avoided when possible. Fords, culverts, and bridges can be used, with stream crossings made at right angles to the streambanks. Crossings should be located where stream channels are straight and not interfere with normal streamflow.
Approaches to stream crossings should climb away from streams to minimize erosion during high water and should be graveled to prevent washing and rutting. Dips and turnouts should be installed to turn water off roads before entering the stream.When crossing streams:
Bridges should be used to cross streams which cannot be forded or that are too large to carry in culverts. Bridges may be constructed of low grade lumber and cull timber on the site.
Stream Crossings can cause the greatest disturbance to streams if not done carefully and properly. Avoid stream crossings if possible, or build structures such as bridges to minimize disturbance to streambanks.
Forest harvesting involves much more than just the cutting of trees. Harvesting activities may include the new construction of roads, the development of a network of skid trails for moving bucked and tree length logs, and the systematic location of log decks or landings for transporting the logs out of the woods.
The potential for soil disturbance during harvesting is greatest on roads, skid trails and log landings where the natural cover has been removed and soil has been compacted by logging equipment. Over ninety-eight percent of all the soil erosion that occurs on forestland in Tennessee can be traced to roads, skid trails and log landings.
The forest manager, logger and forest landowner should first carefully plan the locations of roads, skid trails and log landings before logging begins. This will minimize soil erosion, any potential water pollution problems and save time and construction costs. Planning the harvest and selecting the right harvesting system can achieve many desired forest management objectives such as timber production, tree growth, timber stand improvement and wildlife management, while avoiding soil erosion and water pollution. Several factors should be considered before a logging operation begins. All access roads and skid trails should be carefully planned. Roads, skid trails and log landings should not be located in areas where site damage may occur. Build road and trail systems to allow as much continuous natural drainage as possible. Determine the amount of harvested timber that will be removed from the area and balance the road system to avoid overusing a particular haul road or skid trail. Plan the access systems to minimize traffic over unstable soils or highly sensitive areas.
Schedule the timber harvest during periods of dry weather if possible. Determine the best possible system best suited for harvesting in terms of system impacts on water quality. During the harvest, constrains should be placed on equipment to minimize site disturbance, particularly near streams. Trees should not be felled into the streambed and debris, such as tree tops and limbs, should be kept out of streams. If trees are felled into the stream, the material should be removed after the timber harvest.
Landings should be revegetated as soon as possible after harvesting is completed to stabilize the soil and provide cover.Skid Trails:
Keeping skidders on a few primary skid trails will keep disturbances from logging to a minimum.Avoid:
When you pick up a handful of forest soil, half of it is solid material. The rest is empty pore space that holds water and air. Heavy equipment can squeeze soil pores, reducing the space for water and air. Since trees need water and air for growth, the start of the next forest can suffer from soil compaction.
Certain soil conditions are more likely to lead to compaction. Wet soils are more compactable than dry. The most severe compaction occurs within a few inches of the surface. Unfortunately, that's where seed germination and seedling establishments occurs and where most of the water-absorbing trees roots are found.
New forests also need the nutrients and protection supplied by logging slash. Regeneration of a new forest often requires the removal of some logging slash to prepare the site. Prescribed burning is one tool used to prepare the area for natural regeneration and planting. By carefully monitoring conditions, a fire can be set that consumes only part of the material, leaving the soil humus and large logs undisturbed.
Using herbicides eliminates the problems of compaction and soil disturbance caused by machines. Seedlings may be hand planted and herbicides sprayed to control competing vegetation and help get young trees established.
Site preparation techniques help get the new forest off to a vigorous start. When combined with healthy tree seedlings, either planted or naturally seeded, the result is the next generation forest.
Following forestry operations, roads, skid trails, log landings and other disturbed areas will need to be reseeded properly to stabilize soils and prevent erosion. Some compacted soils may need to be disked or scarified to promote infiltration of water and create suitable seedbed conditions.
Revegetate roads, skid trails, log landings and other areas disturbed by harvesting as soon as possible after logging operations cease.
For roads, determine the acreage from the table below and multiply by the recommended number of pounds per acre for fertilizer, lime and seed:
Road Surface Area in Acres Road Length (Road Width in Feet) Feet Miles 8' 10' 12' 14' 18' 20' 50 .009 .01 .01 .01 .02 .02 .02 100 .019 .022 .02 .03 .03 .04 .05 250 .047 .05 .06 .07 .08 .10 .11 500 .095 .09 .12 .14 .16 .21 .23 750 .142 .144 .17 .21 .24 .31 .34 1000 .189 .18 .24 .28 .32 .41 .46 1500 .284 .28 .34 .41 .48 .62 .69 2000 .379 .36 .48 .56 .64 .83 .92 5000 .947 .92 1.15 1.38 1.61 2.07 2.30 5280 1.000 .97 1.21 1.45 1.70 2.18 2.43
Seeding Group lbs./acre Seeding Dates Tall Fescue (90%)/ 30 Feb. 15-Apr. 1 White Clover 3 Tall Fescue(86%) 30 Feb. 15-Apr. 1 White Clover(14%) 3 Aug. 15-Oct. 15 Tall Fescue(100%) 30 Feb. 15-Apr. 1 Sericea Lespedeza(60%) 30 Mar. 1-Apr. 15 Tall Fescue(30%) 15 Annual Lespedeza(10%) 5 Sericea Lespedeza(79%) 30 Mar. 1-Apr. 15 Weeping Lovegrass(8%) 3 Annual Lespedeza(13%)
Last revised June 17, 1996.