B. Streamside Management Areas (SMAs)
Establish and maintain a streamside management area along surface waters, which is sufficiently wide and which includes a sufficient number of canopy species to buffer against detrimental changes in the temperature regime of the waterbody, to provide bank stability, and to withstand wind damage. Manage the SMA in such a way as to protect against soil disturbance in the SMA and delivery to the stream of sediments and nutrients generated by forestry activities, including harvesting. Manage the SMA canopy species to provide a sustainable source of large woody debris needed for instream channel structure and aquatic species habitat.
1. Applicability
This management measure pertains to lands where silvicultural or forestry operations are planned or conducted. It is intended to apply to surface waters bordering or within the area of operations. SMAs should be established for perennial waterbodies as well as for intermittent streams that are flowing during the time of operation. For winter logging, SMAs are also needed for intermittent streams since spring breakup is both the time of maximum transport of sediments from the harvest unit and the time when highest flows are present in intermittent streams.Under the Coastal Zone Act Reauthorization Amendments of 1990, States are subject to a number of requirements as they develop coastal nonpoint source programs in conformity with this measure and will have some flexibility in doing so. The application of this management measure by States is described more fully in Coastal Nonpoint Pollution Control Program: Program Development and Approval Guidance, published jointly by the U.S. Environmental Protection Agency (EPA) and the National Oceanic and Atmospheric Administration (NOAA) of the U.S. Department of Commerce.
2. Description
The streamside management area (SMA) is also commonly referred to as a streamside management zone (SMZ) or as a riparian management area or zone. SMAs are widely recognized to be highly beneficial to water quality and aquatic habitat. Vegetation in SMAs reduces runoff and traps sediments generated from upslope activities, and reduces nutrients in runoff before it reaches surface waters (Figure 3-9, Kundt and Hall, 1988). Canopy species provide shading to surface waters, which moderates water temperature and provides the detritus that serves as an energy source for stream ecosystems. Trees in the SMA also provide a source of large woody debris to surface waters. SMAs provide important habitat for aquatic organisms (and terrestrial species) while preventing excessive logging-generated slash and debris from reaching waterbodies (Corbett and Lynch, 1985).SMAs need to be of sufficient width to prevent delivery of sediments and nutrients generated from forestry activities (harvest, site preparation, or roads) in upland areas to the waterbody being protected. Widths for SMAs are established by considering the slope, soil type, precipitation, canopy, and waterbody characteristics. To avoid failure of SMAs, zones of preferential drainage such as intermittent channels, ephemeral channels and depressions need to be addressed when determining widths and laying out SMAs. SMAs should be designed to withstand wind damage or blowdown. For example, a single rank of canopy trees is not likely to withstand blowdown and maintain the functions of the SMA.
SMAs should be managed to maintain a sufficient number of large trees to provide for bank stability and a sustainable source of large woody debris. Large woody debris is naturally occurring dead and down woody materials and should not be confused with logging slash or debris. Trees to be maintained or managed in the SMA should provide for large woody debris recruitment to the stream at a rate that maintains beneficial uses associated with fish habitat and stream structure at the site and downstream. This should be sustainable over a time period that is equivalent to that needed for the tree species in the SMA to grow to the size needed to provide large woody debris.
A sufficient number of canopy species should also be maintained to provide shading to the stream water surface needed to prevent changes in temperature regime for the waterbody and to prevent deleterious temperature- or sunlight-related impacts on the aquatic biota. If the existing shading conditions for the waterbody prior to activity are known to be less than optimal for the stream, then SMAs should be managed to increase shading of the waterbody.
To preserve SMA integrity for water quality protection, some States limit the type of harvesting, timing of operations, amount harvested, or reforestation methods used. SMAs are managed to use only harvest and silvicultural methods that will prevent soil disturbance within the SMA. Additional operational considerations for SMAs are addressed in subsequent management measures. Practices for SMA applications to wetlands are described in Management Measure J.
3. Management Measure Selection
a. Effectiveness Information
The effectiveness of SMAs in protecting streams from temperature increases, large increases in sediment load, and reduced dissolved oxygen was demonstrated by Hall and others (1987) (Table 3-10). Lantz (1971) (Table 3-11) also showed the protection that streamside vegetation and selective cutting gave to both water quality and the cutthroat trout population. A comparison of physical changes associated with logging using three streamside treatments was made by Hartman and others (1987) (Table 3-12 (11k)). This study was performed to observe the impact of these SMAs on the supply of woody debris essential to the fish population and channel structure. The volume and stability of large woody debris decreased immediately in the most intensive treatment area, decreased a few years after logging in the careful treatment area, and remained stable where streamside trees and other vegetation remained.
Other experimental forest studies have found that average monthly maximum water temperature increases from 3.3 to 10.5 øC following clearcutting (Lynch et. al., 1985). Increases in stream temperature result from increased direct solar radiation to the water surface from the removal of vegetative cover or shading in the streamside area. Stream temperature change depends on the height and density of trees, the width of the waterbody, and the volume of water (stream discharge), with small streams heating up faster than large streams per unit of increased solar radiation (Megahan, 1980). Increased direct solar radiation also shifts the energy sources for stream ecosystems from outside the stream sources, allochthonous organic matter, to instream producers, autochthonous aquatic plants such as algae.
Brown and Krygier (1970) report the greatest long-term average temperature response following clearcutting and slash disposal on a small watershed in Oregon. The average monthly temperature increased 14 øF compared to no increase on an adjacent, larger watershed that was clearcut in patches with 50- to 100-foot-wide buffer strips between the logging units and the perennial streams. Lynch and Corbett (1990) report less than a 3 øF mean temperature increase following harvesting, with 100-foot buffer strips along perennial streams. They attribute the increase to an intermittent stream with no protective vegetation that became perennial after harvesting due to increased flow. As a result of this BMP evaluation study, Pennsylvania modified its BMPs to require SMAs along both perennial and intermittent streams.
Another benefit of streamside management areas is control of suspended sediment and turbidity levels. Lynch and others (1985) documented the effectiveness of SMAs in controlling these pollutants (Table 3-13). A combination of practices was applied, including buffer strips and prohibitions for skidding, slash disposal, and road layout in or near streams. Average stormwater-suspended sediment and turbidity levels for the treatment without these practices increased significantly compared to the control and SMA/BMP sites.
Practices such as directional felling are designed to minimize stream and streambank damage associated with increased logging debris in SMAs. Froehlich (1973) provides data on how effective different cutting practices and buffer strips are in preventing debris from entering the stream channel (Table 3-14). Buffer strips were the most effective debris barriers. Narver (1971) investigated the impacts of logging debris in streams on salmonid production and describes threats to fish embryo survival from low dissolved oxygen concentrations and decreased flow velocities in intragravel waters. Erman and others (1977) studied the effectiveness of buffer strips in protecting aquatic organisms and found significant differences in benthic invertebrate communities when logging occurred with buffer strips less than 30 meters wide.
b. Cost Information
In 4 of the 10 areas in Oregon studied by Dykstra and Froelich (1976a), the 55-foot buffer strip was the least costly alternative, yet these researchers concluded that no single alternative is preferable for all sites in terms of costs and that cost analysis alone cannot resolve the question of best stream protection method (Table 3-15).
Dykstra and Froehlich (1976b) also found that increased cable-assisted directional felling costs (68 to 108 percent increase) were offset by savings in channel clean-up costs (only 27 percent as much large debris and 39 percent small debris accumulated in the stream for cable-assisted felling), increased yield from reduced breakage, and reduced yarding costs. They also estimated costs for debris removal from streams to be $300 to clean 5 tons of debris from a 100-foot segment, or about $60 per ton of residue removed.
Lickwar (1989) examined the costs of SMAs as determined by varying slope steepness (Table 3-16) in different regions in the Southeast and compared them to road construction and revegetation practice costs. He found SMAs to be the least expensive practice, in general, and to cost roughly the same independent of slope.
The costs associated with use of alternative buffer and filter strips were also analyzed in an Oregon case study (Olsen, 1987) (Table 3-17 (13k)) and by Ellefson and Weible (1980). In the Oregon case study, increasing the buffer width from 35 feet on each side of a stream to 50 feet was shown to reduce the value per acre by $103 undiscounted and $75 discounted costs, approximately a 2 percent increase on a harvesting cost per acre of $5,163 undiscounted and $3,237 discounted. Doubling the buffer width from 35 to 70 feet on each side reduced the dollar value per acre by approximately 3 times more, adding approximately 8 percent to the discounted harvesting costs. Ellefson and Weible also analyzed the added cost and rate of return associated with various filter and buffer strip widths. Doubling the width of a filter strip from 30 to 60 feet increases the cost from $12 to $44 per sale and reduces the rate of return by 0.4 percent. Doubling the width of the buffer strip from 30 to 60 feet doubles the cost and reduces the rate of return by 1 percent. Increasing the width of the buffer strip from 30 to 100 feet triples the cost and reduces the rate of return by 2.3 percent.
4. Practices
As discussed more fully at the beginning of this chapter and in Chapter 1, the following practices are described for illustrative purposes only. State programs need not require implementation of these practices. However, as a practical matter, EPA anticipates that the management measure set forth above generally will be implemented by applying one or more management practices appropriate to the source, location, and climate. The practices set forth below have been found by EPA to be representative of the types of practices that can be applied successfully to achieve the management measure discussed above.
Many States use SMAs. Examples of SMA designation strategies from Florida, North Carolina, Maine, and Washington are presented. Figure 3-10 depicts Florida's streamside management zone (SMZ) designations. Florida's SMZs are divided into a fixed-width primary zone and a variable secondary zone, each of which has its own special management criteria. Table 3-18 presents North Carolina's recommendations for SMZ widths for various types of waterbodies dependent on adjacent upland slope. Maine's recommended filter strip widths are dependent on the land slope between the road and waterbody (Table 3-19). Washington State requires a riparian management zone (RMZ) around all Type 1, 2, and 3 waters where the adjacent harvest cutting is a regeneration cut or a clearcut. A guide for calculating the average width of the RMZ is provided in the Forest Practices Board manual (Washington State Forest Practices Board, 1988)(Figure 3-11).
Enough trees should be left to maintain shading and bank stability and to provide woody debris. This provision for leaving residual trees can be accomplished in a variety of ways. For example, the Maine Forestry Service (1991) specifies that no more than 40 percent of the total volume of timber 6 inches DBH and greater should be removed in a 10-year period, and the trees removed should be reasonably distributed within the SMA. Florida (1991) recommends leaving a volume equal to or exceeding one-half the volume of a fully stocked stand. The number of residual trees varies inversely with their average diameter (Table 3-20). A shading requirement independent of the volume of timber may be necessary for streams where temperature changes could alter aquatic habitat.
Studies by Brazier and Brown (1973) demonstrated that the effectiveness of the SMA in controlling temperature changes is independent of timber volume; it is a complex interrelationship between canopy density, canopy height, stream width, and stream discharge. The Washington State Forest Practices Board (1988) incorporates leave tree and shade requirements in its regulations (Figure 3-12). Shade requirements within the SMA are to leave all nonmerchantable timber that provides midsummer and midday shade to the water surface, and to leave sufficient merchantable timber necessary to retain 50 percent of the summer midday shade. Shade cover is preferably left distributed evenly within the SMA (Figure 3-13). If a threat of blowdown exists, then clumping and clustering of leave trees may be used as long as the shade requirement is met (Figure 3-14).
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