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Relative Effectiveness Not enough interviewees rated this treatment. It is difficult to assess the relative effectiveness of this treatment because no monitoring information was available and few visual observations have been made. Log jams created by felling trees into channels have the potential to detain sediment, but there is little credible confirmation of this potential. Implementation and Environmental Factors Good pre-planning, supervision, and a high level of crew experience are crucial to successful implementation of this treatment. Skilledtree fellers and chainsaw crews are vital to implementation of this treatment. Crews need to be able to judge correct log spacing, position- ing, and adequate contact with the atreambed. This treatment can be implemented only where there is a good supply of dead trees near the channels. Also, care must be taken not to use large trees because they do not work as well as smaller ones. Snags can be felled parallel to channels to support channel banks or in v- ahaped orother patterns to retain woody debris above road culverts. Dania Purpose. Log dame, like straw bale check dame, are used to prevent or reduce sediment inputs into peren- nial streams during the first winter or rainy season following a wildfire. They are constructed of more durable material than straw bale dams. Log dame function by decreasing water velocity and detaining sediment-laden surface runofflong enough for coarser sediments to deposit behind check dams. Decreased water velocity also reduces downcutting in ephemeral channels. Relative Effectiveness. Excellent-40% Good-60% Fair- 0% Poor-0% (Replies = 5) Log dame were rated `excellent° and `goodA in their effectiveness as a BAER treatment by the limited number of interviewees who commented on log dame. Well-built log check dame can be 70 to 80 percent effective in trapping sediment and last 15 to 30 years, The amount of sediment trapped is highly variable depending on the size of the dam. In one location individual log dame were reported to trap up to 40 yd~ (40 ma) o£ sediment without failure. They can be very effective in adding to channel stability and keeping sediment onaite. On the negative side, failures due to undercutting, bypassing, and complete blowout have aggravated erosion preblema by producing deep scour- ing at dam sites and release of large amounts of sediment in pulses. Despite these potential problems and situations where 25 percent failed in the first storm, no one rated log dams as "fair" or "poor" in effectiveness. Implementation and Environmental Factors Like straw bale check dams, a key factor in log dam cen- atruction is having a skilled implementation leader and trained, experienced crews. Log check dams are croatly and labor intensive, requiring six to eight times the labor for installation than straw bale check dame. Design features such ae appropriate size ofwaterahed, dam orientation, log sizes, lateral keying (1.5 to 3 ft (0.4 to 1 m) into banks), spillways, contact with the stream bed, plugging of gaps, and energy dissipaters are important implementation considerations. Some BAER coordinators recommend that log dame never be put in fully functional channels, but others recom- mend that log dams can be used to replace coarse woody debris burned out of small perennial channels. Often rocks are used in conjunction with log dame. Other Factors In some locations, there might not be adequate woody material after a fire to build log dams. Debris Basins Purpose: Debris basins are constructed to treat either the loss of control of runoff and deterioration of water quality, or threats to human life and property. The design of debris basins must be to a standard that they provide immediate protection from flood water, float- able debris, sediment, boulders, and mudflows. They are usually constructed in stream systems with nor- mallyhigh aedimentloads. Their purpose is to protect soil and water resources from unacceptable losses or to prevent unacceptable downstream damage. Debris basins are considered to be a last resort because they are extremely expensive to construct and require com- mitment to annual maintenance. Relatrve Etl`ectrveness Not enough interviewees rated this treatment. In order for debris basins to function they moat be able to trap at least 50 percent and preferably 70 to 80 percent of 100-year flows. A spillway needs to be constructed in the debris basin to aafelyrelease flow in excess of the design storage capacity. The downstream channel should be lined to prevent scour. In some instances excavated pits in ephemeral channels have been used as debris basins. These must be large enough to trap 50 to 90 percent offlood flow. They need to be cleaned annually until abandoned. ImplementatronandEnvironmentalFactors Because debris basins are rather large, they require design by qualified engineers. They are built in depositional or runout areas that have large storage capacity. During construction it is important to maintain the channel gradient. Head cutting can result from improperly located or constructed debris basins. Other Factors Debris basins must be designed with large vehicle access to the basins eo they can be 82 USDA Forest Service Gen. Tech. Rep. RMRS-GTR~3. 2000