Forestry
Specific BMP guidelines apply in Alabama for timber harvesting surrounding streams and wetlands. The tables provided here offer essential information to planning and implementing environmentally responsible harvesting techniques in various scenarios.
Forestry best management practices (BMPs) are implemented to minimize nonpoint source pollution (NPSP) that can occur on active and completed timber harvests. NPSP in forestry consists of sediment reaching waterways and wetlands via erosion from forest roads, skid trails, and stream crossings. Specific BMPs may be required to maintain silvicultural exemption from certain provisions of the Clean Water Act.
BMPs are implemented during active timber harvests and at harvest close-out. The primary goal is to minimize NPSP from entering waterways and wetlands. This means that preparations related to streamside management zones (SMZs), stream crossings, forest roads, and skid trails must begin during the pre-harvest planning stage.
Figure 1. Diagrams on installing water bars, broad-based dips, and culverts. The culvert diagram was modified to the Alabama BMP manual specifications of at least 1 foot of cover above the culvert or half the diameter for larger culverts.
The first step in the planning stage is to determine if there will be any stream crossings and the type of stream that will be crossed (table 1). There are specific BMP guidelines for perennial (table 2), intermittent (table 3), and ephemeral (table 4) streams. Harvesting in wetlands need to follow Alabama BMP guidelines (table 5) along with the fifteen U.S. Army Corps of Engineer baseline BMPs for forest roads and stream crossing construction in wetlands (table 12).
Stream crossing methods can be installed as temporary or permanent crossings and consist of log crossings, fords, culverts, and bridges (table 6). Culvert diameters need to account for peak flow and the Alabama BMP guidelines, which recommend culvert sizes based on drainage (watershed) area (table 7). Temporary crossings need to be removed after the harvest.
Forest road and skid trail BMPs need to be planned out prior to harvesting and implemented and maintained during and after harvesting (close-out BMPs) (tables 8 to 10). Water diversion devices, such as water bars, broad-based dips, and turnouts, are recommended BMPs to reduce erosion and sedimentation from forest roads and skid trails (table 11 and figure 1).
The complete forestry BMP manual is available on the Alabama Forestry Commission (AFC) website at www. forestry.alabama.gov/Pages/Management/Forms/2007_ BMP_Manual.pdf.
Table 1. Stream-type Definitions
Table 2. BMPs for Perennial Streams
Table 3. BMPs for Intermittent Streams
Table 4. BMPs for Ephemeral Streams
Table 5. BMPs for Wetlands
Table 6. Stream-Crossing Methods
It is recommended that all stream approaches and banks be stabilized with hay, enviro mats, grass seed, and hay bales to prevent soil movement back into the stream.
Table 7. Recommended Culvert Diameter Based on the Drainage Area Above the Crossing
Table 8. Permanent Forest Roads
Table 9. Temporary Harvest Roads
Table 10. Skid Trails
Table 11. Water Diversion Device Spacing for Water Bars and Broad-based Dips Based on Percent Slope of Forest Road or Skid Trail
Table 12. U.S. Army Corps of Engineer Baseline BMPs* for Roads and Stream Crossings Within Wetlands and Other U.S. Waters
*BMPs from Section 404, Corps of Engineers Permit Requirements, 40 CFR Part 233.22
Richard Cristan, Extension Specialist and Assistant Professor, School of Forestry and Wildlife Sciences and Carey Potter, BMP Coordinator, Alabama Forestry Commission
Reviewed July 2022, Timber Harvesting Guidelines for Forestry Best Management Practices, FOR-2009