Hillslope Treatments

What – Straw, woodchips or fiber materials are applied to burned areas using ground or aerial application.

Purpose – By providing immediate ground cover, mulch is intended to reduce surface erosion, reduce downstream peak flows by absorbing rainfall, and secure seeds stored in the soil or applied as emergency treatment.  Mulch also provides favorable moisture and temperature regimes for seed germination.

Effectiveness – Straw mulch was reported as highly effective in reducing surface erosion when application rates exceeded 60% ground cover, and sometimes effective in reducing runoff.  Sites prone to high winds reported reduced effectiveness.  A combination of mulching and seeding was reported as more effective than seeding alone in regards to germination, but not necessarily in regards to surface cover.  Wood based mulches (manufactured products and shredded on-site trees) were equal to or more effective than straw mulch in reducing post-fire erosion.

Where

• Areas with moderate- or high-burn severity.
• Due to cost, there usually needs to be prioritization for mulch application, focusing on where there is a threat to life and property. This may include steep slopes adjacent to communities, roads, and infrastructure; critical headwaters that feed municipal water supplies; and waste sites that pose serious environmental threats.

Cost – Straw aerial application $250–930 per acre; ground application $425–1200 per acre.  Based on 1–2 tons per acre application rate (provides average mulch depth of 1–2 inches).  Wood based aerial application $1500–2000.  Additional factors include:

• Location and access.

How to Link – See USDA BAER Catalog page 27 (PDF page 35).

What – Lightweight synthetic or organic mats (netting or blankets) staked to soil surface.

Purpose – Intended to provide temporary (several months to years) soil stability to special interest sites (e.g., heritage resources) until vegetation can establish.  Mats also reduce soil temperature and provide moisture conservation.

Effectiveness – products are expensive, but effective when installed correctly.

Where

• Small areas with high values at risk.

Cost – $0.35–1.00 per square yard + installation (labor).  Additional factors include:

• Site location and access

How to Links – See USDA BAER Catalog page 37 (PDF page 45); and NRCS Erosion Control Mats Fact Sheet.

What – Combinations of organic fibers (e.g., wood shreds, paper, cotton, flax, etc.), tackifiers (i.e., glue), suspension agents, and seeds are mixed together with water and applied to the soil surface via ground or aerial applications. 

Purpose – The matrix formed by hydromulch creates an immediate cover and holds moisture and seeds on steep slopes, which fosters seed germination while holding soil in place.

Effectiveness – Hydromulch may reduce sediment yields during the first few rainfall events (long-term effectiveness is unknown).  Treatments are more effective on short slope lengths vs. longer slopes due to susceptibility to concentrated flows.  This method is wind resistant.  Multiple factors impact effectiveness (e.g., application rates, slope length and steepness, make/brand of tackifier). 

Where

• Aerial application on inaccessible, highly erodible soils following moderate or high fire severity.
• Ground application on highly erodible soils near roads.
• Due to cost, there usually needs to be prioritization for mulch application, focusing on where there is a threat to life and property. This may include steep slopes adjacent to communities, roads, and infrastructure; also critical headwaters that feed municipal water supplies, and waste sites that pose serious environmental threats.

Cost – $2000–3000 per acre for aerial application; $1675–3000 per acre ground application.  Additional factors include:

• Location and access
• Helicopter/fixed-wing aircraft turnaround time
• Helicopter/fixed-wing aircraft production rate

How to Links – See USDA BAER Catalog pages 15 and 22 (PDF pages 23 and 30); and NRCS Hydromulching Fact Sheet.

What – Logs are partially entrenched or/and staked to soil surface parallel to the contour.

Purpose – Intended to slow runoff, cause localized ponding, and capture and store eroded sediment when arranged in a bricklayer pattern on hillslopes. 

Effectiveness – Studies indicated that log erosion barriers may reduce runoff, peak flows, and sediment yields for low intensity rain events (< 1.8” per hour), but are unlikely to have a significant effect for high intensity rain events.  Sediment storage was reported to decrease by 10–15% with each successive rain event.  Although the potential volume of sediment stored is dependent on slope, tree size and length, frequency, and use of berm traps, with proper implementation effective sediment storage and creation of microsites can be achieved.

Please note: some agencies, such as the US Forest Service, no longer endorse this method. However, other users have reported success with this method when logs are properly placed and secured. Please consider the cost, ease of application, and safety, and consult with experts in the post-fire treatment profession who can provide perspective, insight, guidance, and advice in an ever evolving field of practice. 

Where

• Hillslopes with high- and moderate-burn severity.
• Slopes between 25 and 60 percent.
• Soils with high erosion-hazard ratings.
• Watersheds with high values at risk.

Cost – $420–1200 per acre.  Additional factors include:

• Terrain
• Site access
• Frequency of logs
• Labor experience

How to Links – See USDA BAER Catalog page 45 (PDF page 53); and NRCS Log Erosion Barriers Fact Sheet.

What – Felling, lopping, and then scattering trees and brush by hand or mechanical equipment.

Purpose – Intended to provide increased ground cover to reduce raindrop erosion.

Effectiveness – Scattering slash created by chain saw is generally ineffective due to slow labor production rates and the large amount of material needed for adequate soil cover.  However, mechanized equipment (e.g., hydro ax) that masticates material is considered moderately effective.

Where

• Burn sites with moderate or high fire severity.

Cost – $220–1000 per acre.  Additional factors include:

• Topography.

How to Link – See USDA BAER Catalog page 33 (PDF page 41).

What – Fiber rolls, commonly called wattles, are prefabricated rolls manufactured from rice straw and wrapped in degradable netting.  In some cases, on-site woody debris can be rolled in netting to reduce costs.  Rolls are ~ 9 inches in diameter and up to 25 feet long. 

Purpose – Intended for low-surface flows not to exceed 1 cubic foot per second. They are not for stream channels or gullies.  They are intended to reduce erosion by shortening the slope length to slow overland flow velocity as well as trap sediment and provide a seedbed for vegetative recovery.

Effectiveness – Studies indicated that erosion barriers may reduce runoff and sediment yields for low intensity rain events (< 1.8” per hour), but are unlikely to have a significant effect for high intensity rain events.  Wattles reduced total runoff and peak flow rates (Robichaud et al. 2008 and 2010).

Where

• Areas of high- and moderate-burn severity.
• Slopes with < 40% ground cover.

Cost – $1100–4000 per acre.  Additional factors include:

• Location and terrain
• Access
• Experience of crews

How to Links – See USDA BAER Catalog page 51 (PDF page 59); and NRCS Contour Wattles Fact Sheet.

What – Aerial and ground application of seed across large areas.  Native seed mixes are preferred, but non-invasive, non-native seed mixes are also used, often with sterile annual grass seeds or cereal grain seeds.

Purpose – Intended to reduce soil erosion.

Effectiveness – Seeding was generally reported as ineffective (i.e., provided < 60% surface cover) the first year following fire and neutral in subsequent growing seasons following fire.  However, when combined with mulching, the potential for germination may increase as a result of seed and moisture being held by mulch.  Sterile annual seeds and cereal grain seeds that germinate can reduce soil erosion after fire, yet not compete with native grasses in subsequent years.  Please note that seeding has the possibility for introducing invasive and noxious species, so be aware of this possibility.

Where

• Hillslopes with moderate and high fire severity.

Cost – $20–170 per acre.  However, trend analysis indicated costs increased over time (Peppin et al. 2011).  Additional factors include:

• Availability of seed
• Number of species in seed mix
• Implementation time frame
• Number of landowners involved
• Elevation and climate
• Size of fire
• Aircraft type
• Topography
• Proximity of treatment blocks to staging areas
• Weather conditions during seeding

How to Links – See USDA BAER Catalog page 64 (PDF page 72); and NRCS Seeding Fact Sheet.

What – a permeable fabric installed parallel to the contour and anchored with wooden stakes or metal t-posts.

Purpose – Intended to trap sediment and protect areas with high values at risk including heritage resources, water quality, and aquatic resources.

Effectiveness – Studies reported notably high effectiveness when fences were installed properly (i.e., anchored into soil and water allowed to pass through slowly while trapping sediment) and maintained (which requires significant effort and attention).  Robichaud and Brown (2002) measured trap efficiency at over 90 %. 

Where

• Areas accessible for inspection and maintenance.

Cost – $50 per roll (material); $150–250 labor for each fence installation.  Additional factors include:

• Location and terrain
• Frequency of fences
• Soil characteristics

How to Links – See USDA BAER Catalog page 56 (PDF page 64); and NRSC Silt Fence Fact Sheet.

What – Hand tools or mechanical equipment are used to break up and loosen topsoil to increase surface roughness.

Purpose – Intended to break down hydrophobic layer, prepare seedbed, and increase infiltration rate.

Effectiveness – Generally, this treatment did not provide significant improvement (e.g., reduced sediment yield) as compared to no treatment (Rough 2007).

Where

• Areas of high- and moderate-burn severity.
• Slopes with high erosion potential.                                                            

Cost – $245–300 per acre for hand crew; $50 per acre for ATV use.  Additional factors include:

• Location and access

How to Links – See USDA BAER Catalog page 60 (PDF page 68); and NRCS Mechanical Scarification Fact Sheet.