B.4. Stabilization

Stabilization is a project type that reduces or prevents slope failure or ground movement, of a relatively limited extent, that transports earthen debris downhill by sliding, rolling, falling or slumping. Slope failures can involve rock falls and/or debris flow (a mixture of soil, rocks and vegetation) that deposit material at the base of a slope or a slip‐out where a portion of a facility fails and falls to a descending slope. Slope failures can occur in either natural ground or human‐made fill, such as a highway embankment or canyon fill.

The following information highlights eligible activities under the stabilization project type. These activities are not comprehensive, and FEMA encourages applicants and subapplicants to explore innovative ways to stabilize soil. Stabilization projects are eligible under HMGP, HMGP Post Fire, BRIC and FMA.

Under HMA programs, proposed stabilization projects must meet program eligibility requirements, including mitigation of potential structure or infrastructure damage.

Stabilization is an eligible activity that involves projects that reduce risk to structures or infrastructure from erosion and landslides, including installing geosynthetics, surface and subsurface drainage, stabilizing sod, and vegetative buffer strips; preserving mature vegetation; decreasing slope angles; and stabilizing with riprap and other means of slope anchoring. These projects must not duplicate the activities of other federal agencies.

Stabilization can take place in environments ranging from shorelines and streambanks to mountainsides and hillsides, and can be used to mitigate erosion, landslides and avalanches. Stabilization mitigation techniques consist of two main categories: traditional “hard” techniques and nature-based/bioengineered techniques.

Examples of eligible stabilization activities are provided in Table 23.

Table 23: Examples of Eligible Stabilization Activities

Activity	Subactivity	HMGP	HMGP Post Fire	BRIC	FMA
Traditional hard/gray and hybrid techniques	Mechanically stabilized earth	Yes	Yes	Yes	Yes
	Soldier pile walls	Yes	Yes	Yes	No
	Gabion walls	Yes	Yes	Yes	Yes
	Crib walls and bin walls	Yes	Yes	Yes	Yes
Nature-based green technique	Fascines/stakes (e.g., live fascines, pole stakes and post plantings)	Yes	Yes	Yes	Yes
Streambank stabilization	Blankets/mats (e.g., erosion control blanket, live brush mattress, turf reinforcement mat, vegetated gabion mattress, coconut fiber rolls and toe stabilization/revetments)	Yes	Yes	Yes	Yes
	Stone-filled trenches (e.g., vegetated riprap, rootwad revetment, live siltation/tree revetment, trench fill revetment and longitudinal peak stone toe protections)	Yes	Yes	Yes	Yes
	Drainage-promoting measures (e.g., chimney drainage, slope drain and trench drain)	Yes	Yes	Yes	No
	Structural measures (e.g., geocellular containment system, live cribwalls, vegetated articulated concrete blocks, vegetated gabion basket and vegetated mechanically stabilized earth)	Yes	Yes	Yes	Yes
	Large woody debris	Yes	Yes	Yes	No
	Weirs and in-stream structures	Yes	Yes	Yes	No
	Bendway weir	Yes	Yes	Yes	No
	Diversion dike	Yes	Yes	Yes	No
	Engineered log jam	Yes	Yes	Yes	No
	Rock/cross vane	Yes	Yes	Yes	No
Shoreline stabilization	Beach/dune stabilization (e.g., beach nourishment, dune nourishment and plant beach/dune grass)	Yes	Yes	Yes	Yes
	Drainage (e.g., chimney drain, slope drain, trench drain and berm)	Yes	Yes	Yes	No
	Streambank regrading/stabilization (e.g., regrade bank, control runoff, install coir rolls and natural fiber blankets and plant native vegetation)	Yes	Yes	Yes	Yes
	Revetment (e.g., regrade slope, revetment and plant native vegetation)	Yes	Yes	Yes	Yes
	Marsh restoration (e.g., regrading fill, plant native vegetation, edging, sills, breakwater, reef balls, bulkhead, artificial beach, oyster bag/mat and thin layer placement)	Yes	Yes	Yes	Yes
Post-Wildfire	Mulching	Yes	Yes	Yes	No
	Erosion control mats or blankets	Yes	Yes	Yes	No
	Log terraces	Yes	Yes	Yes	No
	Fiber rolls	Yes	Yes	Yes	No
	Hydroseeding	Yes	Yes	Yes	No
	Silt fences	Yes	Yes	Yes	No
Other	Excavation (e.g., removing material and replacing with fill, benching or terracing a slope and reshaping ground surface)	Yes	Yes	Yes	Yes
	Reinforcement (e.g., geosynthetics, toe buttress or berm, deep soil mixing and soil nailing)	Yes	Yes	Yes	Yes
	Drainage (e.g., interceptor trench, horizontal drains and check dams)	Yes	Yes	Yes	No

Traditional measures to stabilize soils often involve the installation of retaining walls. Retaining walls are relatively rigid structures that can be used to strengthen soil and increase resistance to sliding forces in areas where space is limited, such as areas where rights-of-way are restricted. They can also be used to create additional space (e.g., road shoulders or parking areas). Hybrid walls combine wall types and may include both gray and green elements. Examples of hard components or hybrid measures include:

• Mechanically stabilized earth: Mechanically stabilized earth walls are constructed using compacted granular soil fill and geotextiles placed in alternating layers to construct a steepened slope that then may have a wall facing applied.
• Soldier pile walls: Soldier pile walls use a system of steel piles driven at regular intervals (usually 6 to 12 feet) and horizontal members, called lagging, placed horizontally between the piles to retain the soil behind the planks. Soldier pile walls provide stability by resisting the lateral forces of the soil behind the wall.
• Gabion walls: A gabion is a wire cage filled with rocks, concrete pieces, gravel or bricks. A bastion is a gabion that is lined with a geotextile and filled with sand. Gabion walls provide stability by resisting lateral forces behind them. Because gabion walls typically are filled with rocks, they are freely draining and do not allow a buildup of water behind the wall.
• Crib walls and bin walls: A crib wall is a gravity wall system consisting of stacked members that are filled with soil or rock. Bin walls are like crib walls except interlocking bins are stacked on top of each other.

Nature-based and bioengineered stabilization techniques use native vegetation and other suitable plant species with structural components to stabilize and reduce erosion to stabilize soil. These techniques can often be used in conjunction with hard or gray stabilization measures in hybrid approaches. The following sections highlight three nature-based/bioengineered stabilization eligible activities for streambank, shoreline and post-wildfire mitigation. These eligible activities do not represent an exhaustive list, but rather serve to highlight more common nature-based/bioengineered stabilization activities.

In accordance with the Coastal Barrier Resources Act,^[434] HMA programs may assist projects in Otherwise Protected Areas if they do not require flood insurance after project completion.^[435] Projects in a John H. Chafee Coastal Barrier Resources System (CBRS) unit are eligible only if they qualify for one of the exceptions in Section 6 of the Coastal Barrier Resources Act.^[436] That is, projects are eligible if they are consistent with the purposes of the Coastal Barrier Resources Act and qualify as projects for the study, management, protection and enhancement of fish and wildlife resources and habitats.^[437]  

• All projects that occur in or adjacent to CBRS units must meet one of the Coastal Barrier Resources Act exceptions and require that FEMA consult with the appropriate U.S. Fish and Wildlife Service Ecological Services field office.
• Proposed actions carried out within or adjacent to an Otherwise Protected Areas do not require consultation with the U.S. Fish and Wildlife Service.

Proposed bank stabilization projects must mitigate potential structure or infrastructure damage to meet eligibility requirements.

FEMA encourages project teams to coordinate with EHP or HMA staff to determine what data is needed to evaluate the project. The subapplicant should collect and review watershed data, hydrologic and hydraulic data, stream characteristics, soil and geotechnical data, fluvial geomorphic data, climatic and vegetative conditions, habitat characteristics (current and desired), and water quality and pertinent environmental data (current and desired). Important design considerations include site accessibility, channel grade, watershed flows, channel velocities, stream alignment, stream type/geometry, bed material and sediment load, and debris and maintenance needs.

Bioengineering approaches provide a self-stabilizing, long-term solution for many streams and banks damaged by erosion resulting from weather-related factors, construction and wildfires. The underlying principle requires the application of an integrated watershed-based approach that uses sound engineering practices together with ecological principles to assess, design, construct and maintain living vegetative systems. Bioengineering can be used on streambanks that require structural intervention to facilitate the growth of natural vegetation. Once the root system of the vegetation is established, it provides additional stream and bank stability. Successful projects can help repair damage caused by erosion and slope failures; protect or enhance already healthy, functioning systems; and ensure the long-term sustainability of the impaired area.

Measures may include but are not limited to the following categories:

• Fascines/stakes: Cuttings placed perpendicular to the ground or in trenches to improve slope and bank stability; project owners should work with appropriate local agencies to identify which plants to use.
  • Live fascines: Long branch cuttings bundled and placed in a shallow trench to stabilize streambanks and slopes.
  • Pole stakes: Cuttings from native species are embedded perpendicular to the ground in rows.
  • Post plantings: Large diameter cuttings (typically from a cottonwood or willow tree) are planted perpendicular to the ground surface, often among riprap.
• Blankets/mats: Protective layer of fiber, live cuttings or synthetic material placed on slopes for erosion protection.
  • Erosion control blanket: Flexible fiber mats placed over a geosynthetic netting down a slope.
  • Live brush mattress: Thick blanket of live brushy willow cuttings and soils.
  • Turf reinforcement mat: Rolled mat of non-degradable synthetic material that provides a matrix to reinforce the root system of vegetation for erosion protection.
  • Vegetated gabion mattress: Shallow rectangular containers 20 inches to 60 inches deep made of welded wire mesh and filled with rock and substrate to support vegetation.
  • Coconut fiber rolls: Manufactured, elongated cylindrical structures placed at the bottom of streambanks to help prevent scour and erosion in streams with low to moderate velocities (approximately 2.5 to 7 feet per second).
  • Toe stabilization/revetments:Structures or material, such as riprap, placed at the base of a slope to provide resistance against sliding material on a slope or embankment. In streams, these materials also reduce energy from moving water to decrease the likelihood of scour and erosion.
• Stone-filled trenches: Rock-filled trenches placed at the base of a stream bank capable of supporting substrate for vegetation.
  • Vegetated riprap: A layer of stone and/or boulder armoring that is vegetated, optimally during construction, using pole planting, brush layering or live-staking techniques.
  • Rootwad revetment: Structures constructed from interlocking tree materials, primarily intended to resist erosive flows and usually used on the outer bends of streams.
  • Live siltation/tree revetment: A revegetation technique in which cut trees are anchored along the stream bank to secure the toe of the stream bank, trap sediments and create a fish rearing habitat.
  • Trench fill revetment: Constructed by excavating a trench along the top of the bank, placing stone riprap in the trench, and filling the trench with native soil capable of supporting vegetation.
  • Longitudinal peak stone toe protection: A row of well-graded stones is placed parallel to the bank along its toe/base to protect against erosion and scour. The top of the stone is a third to half the bank height and the cross section of the row is triangular. Live poles can be staked among the stones in lower flow velocity environments.
• Drainage-promoting measures: Free-draining material placed on a slope or bank to intercept and control runoff and seepage to ensure long-term stability.
  • Chimney drainage: A subsurface drainage course placed between a natural slope and an earthen buttress fill or other retaining structure.
  • Slope drain: A drainage system used to collect and transport storm runoff down the face of a slope.
  • Trench drain: A drainage trench excavated parallel to and just behind the crest of a stream bank.
• Structural measures: Large retaining structures used to stabilize banks and slopes.
  • Geocellular containment system: Flexible, three-dimensional, high-density polyethylene, honeycomb-shaped earth-retaining structures; can be expanded/backfilled with a variety of materials to mechanically stabilize banks and slopes when applied.
  • Live cribwalls: A gravity-retaining structure consisting of a hollow, box-like interlocking arrangement of structural beams filled with soil and live cuttings.
  • Vegetated articulated concrete blocks: An articulated concrete block system consisting of durable concrete blocks placed together to form a matrix overlay or armor layer while allowing vegetation to grow throughout the system.
  • Vegetated gabion basket: Rectangular containers fabricated from a heavily galvanized steel wire or triple twisted hexagonal mesh. Vegetation is incorporated into rock gabions by placing live branches on each consecutive layer between the rock-filled baskets.
  • Vegetated mechanically stabilized earth: Live cut branches interspersed between lifts of soil wrapped in natural fabric.
• Weirs and in-stream structures: Structures that extend into the stream to direct flows away from banks to reduce erosion.
• Large woody debris: Structures made from felled trees (can include rootwads) to deflect erosive flows and promote sediment deposit at the base of eroding banks.
• Bendway weir: Discontinuous, redirective structures usually constructed of rock, designed to capture and then safely direct the flow through a meander bend; incorporating naturally occurring vegetation enhances aquatic and terrestrial ecosystems.
• Diversion dike: A low berm (or ditch/berm combination) constructed along the crest/top of a streambank.
• Engineered log jam: Structures made from felled trees may be used to deflect erosive flows and promote sediment deposition at the base of eroding banks.
• Rock/cross vane: Structures angled into the flow to reduce local bank erosion by redirecting flow from the near bank to the center of the channel; vegetation planted on nearby streambanks provides long-term stability.

Proposed shoreline stabilization projects must mitigate potential structure or infrastructure damage to meet eligibility requirements. Projects that return a shoreline to previous or pre-disaster conditions without an increase to the level of protection are not eligible.

The subapplicant must, at a minimum, collect and review data and photographs to characterize the project site based on hydrodynamics, morpho dynamics, sediment dynamics, anthropogenic factors, local ecology and water quality, and pertinent environmental data, as described below:

• Hydrodynamics describe the movement of water at the site by processes such as waves, tides and wind-induced currents as well as hydrological processes such as rainfall, infiltration and runoff.
• Morpho dynamics describe the shape and movement of the land’s surface at the site over time. Site orientation, fetch, bathymetry (measurement of depth of water in oceans, seas or lakes), and topography as well as bluff erosion and shoreline change rates are all important morpho dynamics data that should be considered.
• Sediment dynamics describe the movement of sediment, caused by the interaction of wind, water and local topography with individual sediment particles. Important information includes soil composition, sediment grain size distribution and the geotechnical properties of soil at the site.
• Anthropogenic factors include all human-induced impacts at the site. Examples include existing coastal structures (e.g., bulkheads, docks), commercial (e.g., dredging, shipping), recreational (e.g., powerboating, fishing), and fisheries and agricultural (e.g., commercially harvested oyster beds, aquaculture facilities).
• Ecology describes the naturally occurring and interdependent communities of plant, animal and microbial species occurring at the site, and the conditions they depend on. Important information includes common species of local grasses and seagrasses as well as listed threatened and endangered species relying on coastal habitats in the area.

Important design considerations include site accessibility, site grade and orientation, watershed flows, longshore currents, fetch (length of open water over which wind from a given direction can travel to create waves), bed material properties, sediment sources/sinks, debris and maintenance needs, and environmental and historical preservation.

Stabilization methods use living and non-living plant materials together with natural and synthetic construction materials to reduce coastal erosion, establish vegetation and stabilize shorelines. Successful projects can help repair damage caused by erosion and slope failures; protect or enhance already healthy, functioning systems; and ensure long-term sustainability of the impaired shoreline and coastal habitat areas. Commonly used bioengineered shoreline stabilization measures generally focus on reducing wave impacts, mitigating storm surge, minimizing erosion, improving slope stability and/or creating or improving coastal habitat. FEMA will not approve projects that include only sand/sediment placement as a risk reduction measure without accompanying stabilization measures. FEMA encourages the use of nature-based solutions for all shoreline stabilization measures.

Measures may include but are not limited to the following categories:

• Beach/Dune Stabilization:
  • Beach nourishment: Sediment of compatible type (mean grain size and material) is placed on the beach to widen it and add sediment to the shoreline system. Beach nourishment may only be used in combination with other stabilization measures.
  • Dune nourishment: Sediment of compatible type (mean grain size and material) is used to reinforce an eroded dune face or in some cases to create a new dune. Dune nourishment may only be used in combination with other stabilization measures.
  • Beach/dune grass plantings: Native, deep-rooted beach grasses are planted on the dune and upper beach to stabilize added sediment and trap additional sediment.
• Drainage:
  • Chimney drain: A subsurface drainage course placed between a natural slope and an earthen buttress fill or other retaining structure.
  • Slope drain: A drainage system used to collect and transport stormwater runoff down the face of a slope.
  • Trench drain: A drain excavated parallel to and just behind the crest of a coastal bank.
  • Berm: An earthen mound placed at the top of a coastal bank to direct runoff away from the bank fence.
• Streambank regrading/stabilization:
  • Regrade bank: Eroding bank face that is unstable and over steepened is stabilized by reducing the slope. Placing fill at the bank toe and retreating the bank crest are two options.
  • Control runoff: Surface runoff is diverted away from the eroding bank face by creating a berm at the bank crest and/or by installing drywells/French drains to encourage infiltration.
  • Install coir rolls and natural fiber blankets: Blankets made of natural biodegradable fiber are rolled out onto the bank face to temporarily control erosion. Coir rolls, which are dense rolls anywhere from 6 inches to 12 inches in diameter and made of coconut husks, are placed parallel to the bank toe and up the toe face to provide protection from short-term erosion events such as storms. Native, deep-rooted vegetation is planted through the natural fiber components into the bank face.
  • Plant native vegetation: Over time, the vegetation will become established and stabilize the bank as the natural fiber components degrade.
• Revetment:
  • Regrade slope: Flexible, three-dimensional, high-density polyethylene, honeycomb-shaped earth-retaining structures are installed; they can be expanded/backfilled with a variety of materials to mechanically stabilize surfaces.
  • Revetment: Sloped structure placed at the toe and/or face of a coastal bank to dissipate wave energy and reduce erosion; in coastal engineering these are usually made of riprap. Composed of natural materials but not inherently a bioengineering solution.
  • Plant native vegetation: Native vegetation planted on the slope above a revetment as well as within the spaces between rocks in a revetment’s face can increase stability and create habitat.
• Marsh restoration:
  • Regrading fill: Unstable slopes are brought to a lower grade; sediment appropriate for supporting marsh vegetation is introduced if it does not exist.
  • Plant native vegetation: Appropriate native marsh vegetation is planted along the future marsh platform. In areas of very low wave energy this may be all that is needed.
  • Edging: In areas of slightly higher wave energy, edging in the form of coir rolls and/or oyster shell bags can be used to protect the existing vegetated toe of the marsh.
  • Sills: Parallel to vegetated shoreline; reduces wave energy and prevents erosion. Suitable for most areas except high wave energy environments.
  • Breakwater: Offshore structures located parallel to the shore intended to break waves, reducing the force of wave action and encouraging sediment accretion. They are suitable for most areas and can be submerged or exposed. Where appropriate, they can be in the form of a living reef.
  • Reef balls: Reef balls are complex geometric structures that can be installed to serve as an alternative to a traditional breakwater in some environments. They create habitat for shellfish, fish and other marine animals while simultaneously providing protection to the coast by attenuating wave energy.
  • Bulkhead: Vertical wall parallel to the shoreline intended to hold soil in place. They are suitable for high-energy settings and sites with existing hard shoreline structures. Bulkheads are not a bioengineering solution but can sometimes be combined with bioengineering methods to reduce impacts on the local ecology and shoreline system.
  • Artificial beach: In some cases, a gravel and/or cobble beach may be constructed in front of a bulkhead to reduce direct wave impacts and reduce erosion in front of the hard structure.
  • Oyster bag/mat: Oyster bags/mats may be installed offshore of a bulkhead to create habitat and encourage colonization by native oysters.
  • Plant native vegetation: Native vegetation planted landward of a bulkhead can trap airborne sediment and reduce erosion in the case that a bulkhead is overtopped.

Soil stabilization activities post-wildfire (including activities such as flood diversion and reforestation) may be eligible under HMA programs. Landscape or soil stabilization, flood diversion and reforestation following a wildfire event are important because of the increased threat of soil erosion following the destruction of the plant material and litter layer on the ground. Reducing the risk of flood and erosion after a fire through the implementation of soil stabilization, flood diversion and reforestation efforts is important to protecting nearby communities.

Numerous techniques can be used to control erosion and provide soil stabilization after a wildfire event. Short-term stabilization methods include:

• Mulching: Covering the area with a protective straw layer can prevent erosion. Mulch should be covered with plastic netting or adhered to the soil with a tacking agent to minimize loss of straw to adverse weather.
• Erosion control mats or blankets: Fibers, straw or other plant material that protects the soil from precipitation can be used on hillsides and along valleys.
• Log terraces: Dead trees can be placed on the contour, opposite the direction of the slope in an alternating fashion, preventing water from finding a direct path downslope and eroding soil.
• Fiber rolls: Fiber rolls are made from materials such as straw or coconut fiber and are rolled into a tube. They can be used as a temporary fix to control sediment and soil surface runoff and erosion and are particularly useful to protect against sedimentation of water sources near burn sites.
• Hydroseeding: A slurry of seed and mulch mixed with water and fertilizer can be planted to promote growth of native grasses. Grasses help reduce soil erosion because they have an extensive root system to hold soil in place.
• Silt fences: Woven wire and fabric filter cloth acts as a fence to trap sediment from runoff.

Reforestation is a long-term stabilization activity that involves replanting trees and selecting seedlings to restore forest health and reduce erosion. The effectiveness of reforestation depends in part on the rate of forest establishment and appropriate maintenance accomplished during establishment to control invasive species.

Other stabilization projects may be eligible for assistance under HMA programs. FEMA encourages applicants and subapplicants to explore projects not explicitly detailed in the HMA Guide. Some other stabilization activities include:

• Excavation: Excavation is used to remove material from the slope to decrease the forces that drive sliding.
  • Generally, excavation is appropriate only for small slumps or near-surface failures.
  • The excavator should be kept a safe distance from the edge of the slope so it does not impose additional loads at the top of the slope, which could decrease slope stability.
  • The toe material at the bottom of the slope should not be removed.
  • Measures may include:
    • Removing material from the top of the slope and replacing with lightweight fill to reduce driving forces.
    • Benching or terracing the slope by making stair-step cuts.
    • Reshaping the ground surface to reduce the slope angle.
• Reinforcement: The shear strength of soil, which is a combination of frictional forces and cohesion between particles, is what resists downward movement of soil along a slope. Increasing the shear strength of soil helps to improve its resistance to sliding. There are several common methods of strengthening soil to improve sliding resistance. Measures may include:
  • Use of geosynthetics to improve the strength of soil and rock.
  • Constructing a toe buttress or berm at the bottom of the slope.
  • Deep soil mixing, which involves mixing a chemical stabilizer such as cement and/or lime with soil in situ (i.e., in place) to improve soil strength.
  • Soil nailing, typically steel rods or bars installed into the slope at an angle and held in place by cement grout.
• Drainage: Water is a key element that contributes to the stability or instability of a slope for several reasons:
  • The weight of water adds weight to the slope, which increases the driving forces on the slope and can decrease stability.
  • Water can dissolve bonding agents that hold soil or sediment particles together, which reduces the cohesion between particles and can lead to decreased stability.
  • Water can act as a lubricant between an overlying well-drained soil such as sands and gravels and poorly drained soils such as clays and some silts. In this last situation, the water drains more quickly through the well-drained soil and accumulates along its interface with the poorly drained soil because water cannot penetrate the poorly drained soil as quickly.

Improving drainage within a slope can help to improve slope stability. Drainage methods include:

• Install an interceptor trench, which is a drainage system installed near the top of a slope or above the top of a known slide area to collect and direct surface and subsurface water from within permeable soil layers away from the slope.
• Install horizontal drains, which are perforated pipes inserted into the slope at prescribed elevations and spacings to lower the water table to the level of the lowest pipe, which decreases the driving forces by decreasing the water content of the slope soils.
• Install check dams across a drainage ditch to slow the flow of water to reduce erosion.

FEMA will not approve shoreline stabilization projects that include only sand/sediment placement as a risk reduction measure without accompanying stabilization measures. FEMA encourages the use of nature-based solutions for all shoreline stabilization measures. A general list of ineligible activities is included in Part 4.

Bioengineered solutions may be eligible activities under programs by other federal agencies, such as the EPA, USACE and the Natural Resource Conservation Service. FEMA will not provide assistance for activities for which it determines the more specific authority lies with another federal agency or program. These other programs and authorities should be examined before applying for HMA. For more information refer to Part 4.

Applicants and subapplicants must demonstrate that mitigation projects are cost-effective. Projects must be consistent with Part 5.

Projects must meet cost-effectiveness requirements to qualify for FEMA assistance. Cost-effectiveness is evaluated by FEMA using BCA; cost-effective projects have a BCR greater than 1.0.

Stabilization projects that improve or restore the natural environment may be eligible for ecosystem services benefits. For more information refer to Part 5.

Projects must be consistent with Part 6.

Mitigation projects assisted by HMA must be both feasible and effective at mitigating the risks of the hazard(s) for which the project was designed. A project’s feasibility is demonstrated through conformance with accepted engineering practices, established codes, standards, modeling techniques or best practices. The approach should use sound engineering practices and ecological principles to assess, design, construct and maintain living vegetative systems that are blended into the shoreline and the supported coastal ecosystem.

To meet all established objectives, a combination of bioengineering techniques should be considered for a site-specific bioengineering project plan using the following selection criteria:

• Hydrology and hydraulics: The anticipated water surface elevations, wave and surge characteristics, prevailing currents, fetch, ice impacts and related forces should be used to determine the most appropriate type of stabilization structure (hard, bioengineered or a combination of the two) and the location and extent of selected measures.
• Coastal geomorphology: Form and function of the shoreline and its relationship to the coast and surrounding landscape should be studied to understand how the actions taken at the project site will affect the adjacent properties as well as the shoreline system.
• Geotechnical considerations: The type of rock and soil that make up the shoreline and surrounding area influence what measures are appropriate. Soil and geotechnical deficiencies should be evaluated to focus selection of measures that can increase soil erosion resistance and allow for the establishment of vegetation where feasible.

B.4.2.5.2. Design Development for Streambank Stabilization Projects

A combination of bioengineering techniques should be considered for a site-specific bioengineering project plan using the following selection criteria:

• Hydrology: The movement and volume of the flow to and within the stream should be used to determine the best type of stabilization structure (hard/bioengineered).
• Hydraulics: The anticipated water surface elevations, velocities and related forces should be used to determine the location and extent of selected measures. Sudden changes in velocity or shear stresses in areas such as abutments or culverts may necessitate the use of traditional stabilization methods; whenever possible, projects should try to establish vegetation around hardened measures to gradually transition to upland vegetated areas.
• Fluvial geomorphology: Understanding which portions of the stream channel are damaged and what changes might occur to the stream channel in response to human-caused and natural disturbances helps determine appropriate restoration approaches. These strategies must consider the form and function of the stream channel and relationship to the stream and surrounding landscape.
• Geotechnical considerations: The type of rock and soil that make up the stream channel and surrounding area influence what measures are appropriate. Geotechnical deficiencies should be evaluated to focus the selection of measures that can increase soil shear strength using root systems if possible.

A combination of bioengineering techniques should be considered for a site-specific bioengineering project plan using the following selection criteria:

• Geotechnical considerations: The type of rock and soil of the affected area can influence which soil approaches are selected in the stabilization process. Different soil types and conditions affect infiltration rates, which can impact flooding and slope stability. Soils that are hydrophobic may need to be plowed or otherwise broken up to enable infiltration to occur, decreasing surface runoff.
• Silviculture: Long-term stabilization through reforestation is desirable to achieve objectives such as establishing the forest, improving air and water quality, enhancing wildlife habitat and increasing biodiversity. Typically, native species are selected for planting to help achieve these objectives while also preventing the establishment of non-native invasive species. Selection of the appropriate species for planting, determining the appropriate spacing of trees and undertaking planting during the appropriate time of year for the selected species are important factors for achieving long-term stabilization.

It is important to address and comply with all federal, state and local regulations and obtain necessary permits after the completion of conceptual design. State and local law often runs parallel to or branches off from federal law; thus, federal, state and local reviews are often concurrent. Depending on the location, impacts, measures selected and material employed, various permits or certifications may be required before construction.

In general, permits are required from federal, state and local levels. For award, FEMA requires discussions with permitting agencies early in the project development process—even in the conceptual stages—and keeping documentation. Early discussions will likely save time and effort at the project closeout.

A list of pertinent regulations at the federal, state and local levels is included below:

• Water quality permits: Projects involving work within a water of the United States may require a 401 Water Quality Certification from state environmental agencies.^[438] Projects with the potential to affect public drinking supplies through dewatering or other construction activities must contact the state environmental agency to identify regulatory requirements that may apply. Wherever applicable, projects proposing to discharge into surface water must comply with the permit requirements of the National Pollution Discharge Elimination System. Permits from USACE will also likely be required under Section 10 of the Rivers and Harbors Act and/or Section 404 of the Federal Water Pollution Control Act (Clean Water Act), and potentially permission will be required under Section 14 of the Rivers and Harbors Act.^[439]
• Scenic and historic preservation: Permits or approvals may be required for projects that require earthmoving and/or demolition of a structure if the projects are within a certain distance from designated state wild, scenic or recreational, archaeological, and prehistoric or historical sites or structures.
• Tidal wetland and coastal zone permits: Special permit requirements may apply in tidal waters and ocean shorelines in some states. Permits are required for projects including engineering activity that affects dune fields, beaches or shoreline lands.
• Endangered species regulations: Wildlife, natural resources and fisheries departments must be consulted to ensure compliance with state threatened and endangered species regulations.
• Water rights: Each state regulates water rights within its jurisdiction. If a project diverts water or causes changes to a water course, approval or granting of water rights by the state may be required.
• Floodplain management permits: Floodplain management or construction permits may be required by the local floodplain administrator for projects occurring within federally identified special hazard areas (the 1% annual chance floodplain).
• Local stream and wetland ordinances: Many city or county planning departments have local ordinances pertaining to streams and wetlands. Depending on the nature of the project, several permits may be required.
• Local water resources permits: Local or regional irrigation and water districts are empowered to protect water resources in their jurisdiction; permits may be required for certain projects.
• Other: Various agencies, utilities and authorities should be consulted for projects that depend on specific activities and locations.

Table 24 outlines the function and efficiency of streambank stabilization measures.

Table 24: Function and Efficiency of Streambank Stabilization Measures

Measures			Function			Material
Stabilization Measure	Slope Angle	In-stream	Erosion Control	Drainage	Flow Control	Natural Veg.	Geo Synthetic	Stone/ Rock
Fascines/stakes
Live fascines	Low to High	No	Yes	No	Yes	Yes	No	Yes
Pole stakes	Low to Moderate	No	Yes	No	Yes	Yes	No	Yes
Post plantings	Low to Moderate	No	Yes	No	Yes	Yes	No	Yes
Blankets/mats
Erosion control Blanket	No	Yes	Yes	No	No	Yes	Yes	No
Live brush mattress	No	Yes	Yes	No	No	Yes	No	No
Turf reinforce-ment mat	No	Yes	Yes	No	No	No	Yes	No
Vegetated gabion mattress	No	Yes	Yes	No	No	No	No	Yes
Toe Stabilization/Revetments
Coconut fiber rolls	Low to Moderate	Yes	Yes	No	No	No	Yes	No
Stone fill trenches	Low to Moderate	Yes	Yes	No	Yes	No	No	Yes
Vegetated riprap	Moderate	No	Yes	No	Yes	Yes	No	No
Rootwad revetment	Low to Moderate	Yes	Yes	No	Yes	Yes	No	No
Live siltation/tree revetment	Moderate to High	No	Yes	No	No	Yes	No	No
Trench fill revetment	Low to Moderate	No	Yes	No	No	No	No	Yes
Longitudinal peak stone toe revetment	Low to High	No	Yes	No	No	No	No	Yes

All subapplications submitted to FEMA must meet the EHP criteria in Part 4. All subapplications must provide the information described in Part 6 so that FEMA may perform the EHP review.

All subapplications submitted to FEMA must meet the eligibility criteria in Part 4. All subapplications must have a scoping narrative in accordance with Part 6. Project-specific criteria are highlighted below.

All subapplications must include a line-item breakdown of all anticipated costs.

Subapplicants may apply for subrecipient management costs to cover administrative costs. Management costs must be included in the subapplication budget as a separate line item. More information about the requirements for management cost requests can be found in Part 13.

Project implementation includes site preparation, construction, planting, monitoring and aftercare. For the bioengineering design to be successful, implementation must be closely supervised throughout by someone familiar with the implementation of bioengineering projects. Continuity of the interdisciplinary team involved in the design is highly recommended, and consulting with someone who has implemented other bioengineering projects will help ensure the success of the project.

• Streambank stabilization: The optimum time to install bioengineered measures is usually during seasons when stream flows are typically low and dormant cuttings have the highest success rate for propagation. Scheduling the sequence of work is critical to project success. Scheduling considerations include endangered species’ nesting seasons.
• Shoreline stabilization: Ideally, bioengineered measures should be installed in seasons with low storm-wave-induced erosion, when dormant cuttings have the highest success rate for propagation. Scheduling the sequence of work is critical to project success, such as considering endangered species’ nesting seasons.
• Wildfire stabilization: Following a wildfire, there is increased vulnerability to secondary threats, such as floods and mudslides. Slope-stabilizing erosion control practices and forest regeneration can help mitigate floods and landslides. Short-term stabilization methods ideally should be implemented as soon as possible after the fire to help control erosion. Long-term reforestation methods should be undertaken during the appropriate planting season for the native species or seeding method selected.

Recipients are required to report deviations from budget, project scope or objectives in accordance with Part 8. Recipients must request prior approvals from FEMA for budget and program plan revisions.^[440] If the final design is not complete prior to award, once the project is awarded, the design must be finalized by a licensed design professional. Any changes to the scope of work or budget because of completing the final design or to address permitting requirements must be consistent with Part 8. Construction design activities are defined as construction activities; therefore, budget changes involving them must be consistent with Part 8.F.2.

Recipients and subrecipients must closeout projects in a timely manner consistent with Part 9.

In addition to the typical HMA program closeout process, closeout of stabilization projects includes submitting an operations and maintenance plan to FEMA for review prior to project closeout. In the operations and maintenance plan, the recipient must confirm the plan is consistent with the HMA Guide.

At a minimum, the operations and maintenance plan must include all the following information:

• Information demonstrating the completed stabilization project will be maintained to achieve the proposed hazard mitigation.
• A description of the post-closeout maintenance activities that will be undertaken to maintain the project area.
• The period of time the community is committing to maintain the area and/or project site, which must be consistent with the project useful life in the BCA.
• The department and position type that will be responsible for maintaining the project after the construction has ended.
• Estimated costs for annual maintenance of the project.
• The schedule for completion of the maintenance activities.