Forestry

POLLUTANTS AND SOURCES

BEST MANAGEMENT PRACTICES

REFERENCES

INTRODUCTION

Sound forest management must involve controlling nonpoint-source pollution during and after silvicultural activity. The harvest of needed forest resources should not be at the expense of water quality, forest productivity, or aquatic life. Information from experimental watersheds suggests that silviculture impacts water quality by causing erosion and raising sediment/turbidity levels and dissolved nutrient concentrations, and by changing water temperatures (Lynch et al, 1985). Several BMPs can be implemented to lessen the detrimental effects of forestry activity on a watershed.

POLLUTANTS AND SOURCES

The major silvicultural practices that contribute to NPS pollution include:

• Road Construction and Use;
• Timber Harvesting;
• Mechanical Equipment Operation;
• Prescribed Burning;
• Site Preparation;
• Fertilizer and Pesticide Application.

Pollutants generated from these sources can include:

• sediment lost via water, ice, or wind;
• nutrients from forest fertilizer application;
• chemicals from pesticides (herbicides, insecticides, and fungicides);
• temperature changes resulting from riparian vegetation removal and sediment additions;
• streamflow increases caused by vegetation removal.

BEST MANAGEMENT PRACTICES

Before BMPs can be implemented, the site must be rated and its sensitivity determined. By necessity, the practices that surround site preparation, cultivation, and harvesting alter the ecosystem in varying degrees during the life of the operation. Without question, BMPs are needed to conserve soil and water resources, thus extending the life of the ecosystem and downstream resources. The following narrative outlines how the activities that are necessary to the initiation, life, and retirement of a silvicultural operation revolve around the use and continuance of best management practices.

Proper preharvest planning is the primary BMP for silvicultural activities. This essential planning phase should include scheduling activities for the least environmental impacts, rating and determining the site sensitivity, and establishing restrictive zones. These measures minimize the generation and delivery of organic matter and sediment to adjacent waterways. BMPs for actions during harvest should be established during preharvest planning.

PREHARVEST MEASURES

Establishing Restrictive Zones

The land occurring within 300 feet of the water course, the Discretionary Zone (DZ), is examined using either maps and photos or on the ground and a rating is assigned. BMPs are recommended on critical areas--the DZ and SMZ (Neuman, 1988).

A streamside management zone, or SMZ, should be positioned along all perennial and intermittent streams as well as lakes of 10 acres or more to provide protection from excessive sediment, nutrients, logging debris, forest chemicals, and temperature changes. The width of the SMZ depends the sediment released from the site which is a function of the soil classification. There are two classifications of SMZ: fixed primary and variable secondary.

The primary SMZ is 35 feet wide on perennial streams and lakes greater then 10 acres; they are not necessary on intermittent streams. Selective timber harvesting is allowed with the primary SMZ provided a prescribed volume of trees is left standing (see Table 1). The secondary zone stretches beyond the primary zone to compose the total SMZ. The width of the secondary zone relies on the Site Sensitivity Class (SSC). In this zone, complete timber harvesting is allowed, since shade is not necessary in this region (see Table 2).

The SSC, which is used to rate a site, is based on sedimentation potential. The rating is based on soil erodibility, degree of slope, and closeness to a waterway, all of which cannot be significantly altered by man. The types of best management practices used are determined by the SSC (Neuman, 1988).

Within the entire SMZ, certain silvicultural practices are permitted. They include direct seeding, hand planting or machine planting on the contour, prescribed burning except on slopes 18 percent or greater (all 5 and 6 Site Sensitivity Classes), and basal application of herbicides and insecticides. Practices that are not allowed within either zone include mechanical site preparation, fertilization, and aerial application or mist blowing of herbicides and insecticides. Other excluded activities include loading decks and log buncing points. Access roads are only allowed to lead directly to the edge or crossing of a waterway. Firelines are only allowed in the SMZ during emergencies (Neuman, 1988).

Table 2. Recommended widths of primary and secondary streamside management zones for perennial streams and lakes 10 acres or larger, and SMZ widths for intermittent streams (expressed as horizontal distance in feet from the mean high water mark).

Scheduling

Harvest and construction in warmer regions should be scheduled during dry periods/seasons. Schedule these operations for winter months in temperate zones where snow cover and frozen ground can be used as an advantage (USEPA, 1993).

FORESTRY MEASURES

Fertilizer and Pesticide Application

Fertilizers and pesticides applied to a site may affect surface and groundwater quality. Improper application can increase nitrate nitrogen, phosphorus, and organic compounds in runoff and groundwater resulting in lake eutrophication, fish kills, and poisoned groundwater. Aerial application should not be used within the SMZ and quick release formulations should be discouraged (Neuman, 1988). Fertilizers should be applied during periods of maximum plant uptake. Use IPM, integrated pest management, techniques (USEPA, 1993).

Broad-based Dips: Dispersion of road and ditch drainage from heavily-used permanent roads is best accomplished with broad-based dips. Broad-based dips are periodic reversals in the grade of the road to reduce runoff velocity and slope length. Recommendations for spacing of broad-based dips are shown in Table 3 below (Neuman, 1988).

Culverts and Cross Ditches: To preserve the integrity of permanent access roads it is crucial to properly transport and disperse drainage. Cross ditches are shallow basins built diagonally across a road (Neuman, 1988). Culverts, though built to accomplish the same task as cross ditches, are metal, wooden, plastic, or concrete conduits laid over or under the road (Florida DOACS, 1990). The table below gives spacing recommendations for culverts and cross ditches (Neuman, 1988).

Water Bars: Drainage from temporary roads, firelines, and skid trails is accomplished with water bars (see table below). Water bars are 1-3 foot banks of earth built across a road surface with the ends extending past the road and ditch (Neuman, 1988).

Water Turnouts: Channels that drain water away from roads into vegetated areas for dispersion are known as water turnouts. Water turnouts are only recommended for permanent roads in the discretionary zone (see table below) (Neuman, 1988).

Site Preparation

Commonly used site preparation practices include burning, chop and burn, KG blading, bedding, and combinations of mechanical site preparations. All of these practices, which vary with soil type, slope, residual vegetation, tree species, and costs involved, expose bare ground to some degree, resulting in soil loss and stream degradation (Neuman, 1988). Therefore, none of these activities should be employed within the SMZ. Heavy equipment should be banned from the SMZ as well. Trees cut in the SMZ should be directionally felled away from the streams (USEPA, 1993).

Timber Harvesting: Removing trees improperly or from certain locations in a watershed can increase soil loss and water temperatures. When timber is removed carelessly from steep slopes, valuable soil may be lost and water quality may in turn deteriorate. Trees near the water's edge should not be harvested since they shade the watercourse, keeping the water temperatures down in the warmer months. Lower water temperatures translate into higher dissolved oxygen concentrations (Neuman, 1988). Landings should only be as large as needed in order to safely and efficiently store logs and load trucks. Drainage and erosion control structures should be installed around landings. Logs should be skidded end to end uphill toward landings when possible, following the contour of the slope. Logs should be yarded uphill and cable yarding should be avoided in or across waterways. Precautions should be taken to avoid leaks and spills of petrochemicals, including spill contingency plans. A number of BMPs can be used to minimize erosional losses from logging activities, and some of these are listed below.

Brush Barriers: Brush barriers are piles of slash material piled at the toe slope of a road or at the outlets of culverts, turnouts, dips, and water bars. They should also be installed at the foot of fills if the fills are located inside 150 feet of a defined stream channel (Swift, 1988).

Check Dam: A small porous or nonporous dam constructed across a drainageway to reduce channel erosion by restricting flow velocity. Check dams should not be used in live streams. They can serve as emergency or temporary measures in small eroding channels that will be filled or permanently stabilized at a later date. They can also serve as permanent measures that will sediment in over time in gullies, which is a more common usage in range and agricultural settings. In permanent usage, when the impounded area is filled, a relatively level surface or delta is formed over which the water flows at a noneroding gradient. the water then cascades over the dam through a spillway onto a hardened apron. By constructing a series of check dams along the gully, a stream channel of comparatively steep slope or gradient is replaced by a stair-stepped channel consisting of a succession of gently slopes with "cushioned" cascades in between (Gray and Leiser, 1982). For temporary usage, consider the alternatives of protecting the channel bottom with materials such as riprap, geotextile, biodegradable, or other matting, or other linings in combination with vegetation before selecting check dams (Smolen et al., 1988). Dams can be nonporous, such as those constructed from concrete, sheet steel, or wet masonry, or they can be porous, using available materials such as straw bales, rock, brush, wire netting, boards, and posts. Porous dams release part of the flow through the structure, decreasing the head of flow over the spillway and the dynamic and hydrostatic forces against the dam. Nonporous dams are durable, permanent, and more expensive while porous dams are simpler, more economical to construct, and temporary. For construction details on a number of temporary check dam types, see Gray and Leiser (1982).

Grade Stabilization Structure: A structure designed to reduce channel grade in natural or constructed watercourses to prevent erosion of a channel that results from excessive grade in the channel bed or artificially increased channel flows. This practice can prevent headcutting or stabilize gully erosion. Grade stabilization structures may be vertical drop structures, concrete or riprap chutes, gabions, or pipe drop structures. Permanent ponds or lakes may be part of a grade stabilization system. Concrete chutes are often used as outlets for large water impoundments where flows exceed 100 cfs and the drop is greater than 10 ft. Where flows exceed 100 cfs but the drop is less than 10 ft., a vertical drop weir constructed of reinforced concrete or sheet piling with concrete aprons is generally recommended. Small flows allow the use of prefabricated metal drop spillways or pipe overfall structures. Designs can be complex and usually require detailed site investigations. Design of large structures (100 cfs) requires a qualified engineer. The National Engineering Handbook (Drop Spillways, Section 11, and Chute Spillways, Section 14) prepared by the USDA Natural Resources Conservation Service gives detailed information useful in the design of grade stabilization structures (Smolen et al., 1988).

Revegetation: Seeds and plants that are adapted to the site should be used. If at all possible, seed before the rainy season and use mulch and slow-release fertilizers, where needed. Protect areas from damage from animals and vehicles; inspect often and repair immediately.

Riprap: Riprap is a layer of stone designed to protect and stabilize areas subject to erosion, slopes subject to seepage, or areas with poor soil structure. Riprap is used on slopes where vegetation cannot be established, channel slopes and bottoms, stormwater structure inlets and outlets, slope drains, streambanks, and shorelines. It should be a well-graded mixture of stone sizes, and should be underlain by a filter blanket of gravel, sand and gravel, or synthetic material to prevent soil movement into or through the riprap (Smolen et al., 1988). Riprap can assist in all stages of a BMP system.

Sediment Basin/Rock Dam: An earthen or rock embankment located to capture sediment from runoff and retain it on the site, for use where other on-site erosion control measures are not adequate to prevent off-site sedimentation. Sediment basins are more permanent in nature than sediment traps, and can be designed as permanent features. Basins are most commonly used at the outlets of diversions, channels, slope drains, or other runoff conveyances that discharge sediment-laden water. Earthen basins should use barrel and riser discharge structures, while rock dams can be designed to discharge over the top of the embankment, where a crest should be constructed as the low point. Smaller gravel should line the inside face of the rock dam (Smolen et al., 1988). Sediment basins and rock dams assist in the third, capture, stage of a BMP system.

Sediment Fence (Silt Fence)/ Straw Bale Barrier: A temporary sediment barrier consisting of filter fabric buried at the bottom, stretched, and supported by posts, or straw bales staked into the ground, designed to retain sediment from small disturbed areas by reducing the velocity of sheet flows. Because silt fences and straw bales can cause temporary ponding, sufficient storage area and overflow outlets should be provided. Ends must be well-anchored (USEPA, 1993). Sediment fences and straw bale barriers assist in the third, capture, stage of a BMP system.

Sediment Trap: A small, temporary ponding basin formed by an embankment or excavation to capture sediment from runoff. Traps are most commonly used at the outlets of diversions, channels, slope drains, or other runoff conveyances that discharge sediment-laden water. It is important to consider provisions to protect the embankment from failure from runoff events that exceed the design capacity. Plan for nonerosive emergency bypass areas. Make traps readily accessible for periodic maintenance. High length-to-width ratios minimize the potential for short-circuiting. The pond outlet should be a stone section designed as the low point (Smolen et al., 1988). Sediment traps assist in the third, capture, stage of a BMP system.

Vegetated Filter Strip (VFS): A low-gradient vegetated area that filters solids from overland sheet flow. VFSs can be natural or planted, should have relatively flat slopes, and should be vegetated with dense-culmed, herbaceous, erosion-resistant plant species. The main factors influencing removal efficiency are the vegetation type and condition, soil infiltration rate, and flow depth and travel time, which are affected by size of contributing area, and slope and length of strip (Smolen et al., 1988). A filter or buffer strip should be provided between the stream and area of logging activity. Channelized flows decrease the effectiveness of VFSs. Level spreaders are often used to distribute runoff evenly across the VFS (Dillaha, 1989; USEPA, 1993).

LINKS

• US EPA Office of Water, Nonpoint Source Pollution - Forestry
• USDA Forest Service
• Forestry Best Management Practices in Watersheds
• North Carolina Forest Service - Water Quality
• South Carolina Forestry Commission BMP
• Wisconsin Department of Natural Resources - BMP for Water Quality

REFERENCES

FDACS, 1990. Silviculture Best Management Practices Manual. Florida Department of Agriculture and Consumer Services, Division of Forestry, Tallahassee, FL.

Gray, D.H., and A.T. Leiser, 1982. Biotechnical Slope Protection and Erosion Control. Van Nostrand Reinhold Company, New York, NY.

Lynch, J.A., E.S. Corbett, and K. Mussallem. Best Management Practices for Controlling Nonpoint-source Pollution on Forested Watersheds. J Soil and Water Conservation, 40(1):164-167.

Neuman, L. , 1988. Silviculture and Best Management Practices. Florida Department of Natural Resources, Tallahassee, FL.

Smolen, M.D., D.W. Miller, L.C. Wyatt, J. Lichthardt, A.L. Lanier, W.W. Woodhouse, and S.W. Broome, 1988. Erosion and Sediment Control Planning and Design Manual. North Carolina Sedimentation Control Commission, NC Dept. of Natural Resources and Community Development, Raleigh, NC.

SCFC, 1994. South Carolina's Best Management Practices for Forestry. South Carolina Forestry Commision, Columbia, SC.

Swift, L.W., Jr., 1988. Forest Access Roads: Design, Maintenance, and Soil Loss. Pages 313-324. In W. T. Swank and D. A. Crossley, Jr. (eds.), Forest Hydrology and Ecology at Coweeta. Springer-Verlag, New York, NY.

USEPA, 1993. Guidance Specifying Management Measures for Sources of Nonpoint Pollution In Coastal Waters. EPA-840-B-92-002, January 1993. U.S. Environmental Protection Agency, Office of Water, Washington, DC.

NCSU Water Quality Group

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