Contour-Felled Logs (Log Erosion Barriers, Log Terraces, Terracettes)

System for detaining runoff and sediment on slopes by felling standing timber (snags) along the contour, delimbing and anchoring the logs, and backfilling to create small detention basins. Also known as contour-felling, contour log terraces, log erosion barriers (LEBs). In some regions, contour-felling describes only felling the standing timber in the direction of the contour but not anchoring or backfilling. 

Purpose: Contour-felled logs reduce water velocity, break up concentrated flows, and induce hydraulic roughness to burned watersheds. Sediment storage is a secondary objective. The potential volume of sediment stored is highly dependent on slope, the size and length of the felled trees, and the degree to which the felled trees are adequately staked and placed into ground contact.

Relative Effectiveness: Excellent-29% Good-37% Fair-14% Poor-20% (Replies = 35).   The effectiveness of contour-felling covered the spectrum from “excellent” to “poor,” although more ratings were “excellent” or “good” (66 percent) than “fair” or “poor” (34 percent). Some personnel reported 100 percent of logs functioning, while others reported 0 percent functioning. Site conditions, installation quality, climate, and the quality of materials are major factors in determining relative effectiveness. In some instances contour-felled log barriers have filled with sediment following the first storm event after installation, while others have taken 1 to 2 years to fill.

Implementation and Environmental Factors: Good planning, proper implementation, and knowledge of environmental factors are crucial to the success of contour-felling. This ESR treatment is expensive, technically demanding, and dangerous work, so crew skill and experience and good supervision are important. Attention to felling and delimbing safety rules is paramount. Logs must be placed on the contour, put in contact with the ground, and properly anchored. If these three items are ignored, failure is assured. This treatment needs to be implemented in a very methodical and meticulous manner. Increased installation speed or area covered will not make up in effectiveness that can be lost by poor installation. Ground contact can be assured by adequate delimbing beneath each log, leaving branches downhill, trenching, and back-filling. In some instances machinery has been used to make ground contact trenches, but the usual method is to excavate with hand labor due to equipment and slope limitations. Trenching to seat contour-felled logs has an additional benefit in that it can help to break up hydrophobic layers in the soil. Anchoring can be done with wooden or re-bar stakes where slopes are steeper, but should be of sufficient frequency and depth to prevent movement of the logs.

Shallow, rocky soils that are very uneven are problematic for anchoring, so care must be taken to ensure that logs are adequately secured to the slope. Overly rocky and steep slopes should be avoided, because benefits gained from contour-felling treatment can be easily offset by extra implementation time required and limited stabilization of small amounts of soil. Gentler slopes and finer textured soils (except clayey soils) lead to better installation and greater sediment trapping efficiency. Slopes less than 40 percent are recommended for successful contour-felling. Slopes greater than 75 percent present significant installation safety hazards and should be avoided. In some instances, only the lower portions of slopes near ephemeral or perennial channels have been treated. In highly erosive soils derived from parent material such as granitics or glacial till, so much sediment can be mobilized that it might overwhelm small contour-felled logs.

Availability of adequate numbers of straight trees also affects this treatment. Specifications require logs from burned trees 15 to 20 ft (4.5 to 6 m) in length with diameters of 4 to 12 in (100 to 305 mm). Placing tree stems 10 ft (3 m) apart on slopes over 50 percent, 15 ft (4.5 m) apart for slopes of 30 to 50 percent, and 20 ft (6 m) apart for slopes less than 30 percent would require 2000 to 4000 linear ft/ac (1500 to 3000 linear m/ha ) of tree bole on some sites. A shortage of dead timber or large numbers of small diameter trees could place limitations on the contour-felled treatment area. Crooked stems, such as oak, are often readily available, but they are not useable or cost-effective for contour-felling treatment. Cutting trees for contour-felled log barriers reduces the number of snags for birds to use. However, it often increases vegetation cover when plants become established in fine sediments trapped on the uphill sides of the felled logs. Contour-felled logs should be placed in a random pattern to ensure a more “natural” appearance and avoid patterns which might aggravate runoff.

Contour-Felled Logs (Log Erosion Barriers, Log Terraces, Terracettes) Implementation Guidelines


The objectives for log erosion barriers are:

To foster infiltration and to slow overland runoff.

To prevent and reduce erosion, rills, and loss of ashes from the site.


The sites where this methodology is often used is on steep, productive soils that have burned under a high intensity and have hydrophobic soils.

Areas that have standing burned trees.

Slope Gradient is generally between 30% to 60%.

Watershed Condition --Log Erosion barriers are most effective when constructed in watersheds with a moderate to severe degree of damages from a fire such as:

Abundant hillslope sediments that were stable before the fire and have been released by the fire.

Watershed soils are moderate to strongly hydrophobic (water beads at least 3 minutes or over 10 minutes before infiltrating).

Ground cover density of effective organic materials has been reduced to less than 20% as a result of the fire. 

Needle cast from overstory trees is expected to provide less than 50% ground cover before the first flood-producing precipitation event. 

Dominant vegetation on adjacent watershed is trees, seedling shrubs, or other vegetation that requires a lag time to recover, but is neither perennial grass, nor annual grass that will recover in year one. 

Size of fuels consumed by the fire is mostly 3/4", diameter or larger. This judgment is made by observing the residual fuels.

If a Geographical Information System database is available, three site criteria can be used to locate potential log terrace sites:

High Risk Watershed Condition (defined in mapping burned areas)

Slopes greater than 30% and less than 60%.

Tree size class that indicates trees present are at least 6 inches DBH or some measure of tree size such as tree canopy 15% or greater.

Log erosion barrier sites are often given companion treatments such as aerial seeding and instream treatments, especially if there are high values at risk.


Work includes selecting only those trees that meet the criteria, felling, limbing, trenching and backfilling above each log.

Locating -- Log erosion barriers are implemented only on hillslopes designated by the project leader and approved in the treatment plan. The perimeter of each area is clearly flagged with a discrete color code, marked on the ground with a wooden stake and indexed both on the staked and on the project map. The size may be noted both on the ground and on the map.

Spacing -- The preferred density is 400 to 600 linear feet of logs per acre, but can go as low as 300 linear feet of logs per acre if trees are scarce. To judge when the target density is achieved, inventory a 1/5th acre plot.

Positioning -- Logs must be level, and positioned perpendicular to the overland flow path of water. Where the log cannot be leveled against stumps or natural features, a short stake may be driven into the soil to keep from rolling. The stake can be a tree linb, rock or sawn stake.

Tree Size -- The preferred tree is 6" to 8" DBH and unmerchantable. Trees up to 10" DBH can be used where others are not available within a reasonable distance. Trees that could be used as sawlogs are never selected. In areas where acceptable trees are not available, trees as small as 4" DBH can be selected. In stands of smaller trees, the small stems can be felled in groups of 3 to 6 stems per group. The best, and most durable trees are those that are suppressed and growing in the understory. Down logs may also be used if they are solid enough to act as an erosion barrier.

Species -- The least valuable trees will be used.  Conifers are preferable to hardwoods,  Only dead trees of any species should be cut for logs. No trees with green leaves/needles should be used.

Stumps -- Stumps should be at least 12" high, but on steeper slopes can go to 18" high. Stumps make a good place to secure the log on the uphill side.

 Logs -- Should be approximately 10 to 20 feet long. Longer logs are difficult to handle and not easily bedded into the soil. The entire length must be in contact with the soil, and positioned on the contour, perpendicular to the slope.

Bedding -- Each log must be bedded in a trench approximately 2" deep, with an upslope backfill to seal the log to the soil such that water does not flow beneath the log. Both the trench and backfill are made with a Hazel Hoe scalping tool.

Progress -- It is best to begin at the top of the unit and work down. That way the people bedding the logs can stay out of the way of falling trees. It is also easier to determine how the water would flow looking down on an area and easier to determine the staggered spacing of logs.

Teams -- The most efficient team is one person sawing trees, followed at a SAFE distance by two people trenching and bedding the logs. 

Equipment -- Chain saw with safety equipment; Hazel Hoe or mattock for bedding logs; a single bit axe is sometimes used to cut and bound stakes: small 8" carpenter level to periodically check logs.

Protection of Cultural Resources -- The workers must protect all cultural resources by not dropping trees or bedding logs on these sites. Each site must be reported to the team leader.

Bypass Areas -- There will be islands within most designated treatment blocks that are low priority for log erosion barriers. Here are a few examples:

Trees that have been killed by the fire, but still retain their needles. These areas can be bypassed if needle cast will stabilize the site.

Slopes that are greater than 60% with poor footing can be bypassed.

Where surface rock, 4" in diameter and larger cover over 60% of the soil surface, a partial treatment can be achieved by felling the required number of trees, but without cutting it into logs, or bedding it.

Where trees are 12" diameter or greater, and no candidate trees can be found.

Openings where trees do not grow should be bypased.

If not enough suitable trees are available, only those that meet the selection criteria are felled.

Production -- A well trained crew can achieve 1+ acre of log terraces per person day. Experienced crews can treat 3+ acres per person day.


Costs do vary slightly from area to area but some of the factors that must be considered include the following:

Availability of labor supply, such as experienced contract crews.  The use of force account crews should be avoided because training takes considerable time, and other duties may take them away before the completion of log erosion barriers. In addition, costs may increase dramatically with force account crews. Inmate crews are another option. It is important to consider the time for training and inspection of new crews. In addition, in-mate crews often have a shorter work day and are constrained in terms of how far they can go.  

The approximate acreage for treatment must be appropriate for the size of the potential labor supply and the expected time available before winter weather closes the area.

The expected success of alternative treatments (such as seeding, tilling and other hillslope treatments) are low or delayed. In some cases the log terracing may be implemented with more confidence than other treatments that may not be immediately effective.

The use of test plots for bidders has been used. This enables potential bidders to look at what is the desired result and have a clear idea of the expectation of the unit.

In areas where logs are limited, some units have factored in a certain amount of hand trenching that can be used alone or in combination with log erosion barriers.