Environmentally Sensitive Channel- and Bank-Protection Measures (2005)

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29 APPENDIX A DESCRIPTIVE LIST OF CHANNEL- AND BANK-PROTECTION TECHNIQUES The following techniques are described below: • River training ° Spur dikes ° Vanes ° Bendway weirs ° Large woody debris structures ° Stone weirs ° Longitudinal stone toe ° Longitudinal stone toe with spurs ° Coconut fiber rolls ° Vegetated gabion basket ° Live cribwalls ° Vegetated mechanically stabilized earth ° Live siltation ° Live brushlayering ° Vegetated floodways ° Meander restoration • Bank armor and protection ° Vegetation alone ° Live staking ° Willow posts and poles ° Live fascines ° Turf reinforcement mats ° Erosion control blankets ° Geocellular containment systems ° Rootwad revetments ° Live brush mattress ° Vegetated articulated concrete blocks ° Vegetated riprap ° Soil and grass covered riprap ° Vegetated gabion mattress ° Cobble or gravel armors ° Trench fill revetment • Riparian buffer and stream opportunities ° Live gully repair ° Vanes with J-hooks ° Cross vanes ° Boulder clusters ° Newbury rock riffles • Slope stabilization ° Diversion dike ° Slope drain ° Live pole drain ° Chimney drain ° Trench drain ° Drop inlet ° Fascines with subsurface drains ° Slope flattening ° Stone-fill trenches RIVER TRAINING SPUR DIKES Spur dikes, deflectors, or groins are transverse structures that extend into the stream from the bank and reduce erosion by deflecting flows away from the bank. Transverse river training structures often provide pool habitat and physical diversity. Two to five structures are typically placed in series along straight or convex bank lines where flow lines are roughly parallel to the bank. Spurs, groins, and deflectors have no spe- cific design criteria regarding crest height, crest slope, or upstream angle and therefore differ from vanes and bendway weirs. Earthen core spur dikes are groins constructed with a soil core armored by a layer of stone. Deflectors can also be constructed from natural materials, such as Large Woody Debris (LWD), or LWD embedded with rock, and designed to provide biologic benefits and habitat restoration. Stone spurs capped with a prism of earth reinforced with live fascines are referred to as “live booms.”

30 VANES Rock vanes are discontinuous, redirective structures angled upstream 20 to 30 degrees. Generally, two or three vanes are con- structed along the outer bank of a bend in order to redirect flows near the bank to the center of the channel. Typically, vanes project 1/3 of the stream width. The riverward tips are at channel grade, and the crests slope upward to reach bankfull stage elevation at the key. Rock vanes can preclude the need for rock armor and increase vegetative techniques as the high flows are redirected away from the bank. Vanes can increase cover, backwater area, edge or shore- line length, and the diversity of depth, velocity, and substrate. Vari- ations include cross vanes and rock vanes with J-hooks. BENDWAY WEIRS Bendway weirs are discontinuous, redirective structures usually constructed of rock, designed to capture and then safely direct the flow through a meander bend. A minimum of five structures are typically placed in series (the series are known as “weir fields”) along straight or convex bank lines. Bendway weirs differ from spurs and vanes in that they form a control system that captures and directs the streamflow through the weir field, usually all the way through the bend (hence the name bendway weirs). Bendway weirs are generally longer (1/3 to 1/2 stream width) and lower than barbs or spurs, flat crested, and designed to be continuously submerged or at least overtopped by the design flows. Transverse river train- ing structures often provide pool habitat and physical diversity. LARGE WOODY DEBRIS STRUCTURES Large woody debris (LWD) structures (also known as engi- neered log jams) made from felled trees may be used to deflect erosive flows and promote sediment deposition at the base of eroding banks. Root wads, consisting of a short section of trunk and attached root bole, can also be used or incorporated into the structures. Using the classical spur design criteria and methods, the placement of LWD structures can be designed to achieve opti- mum benefit for both aquatic habitat and bank protection. STONE WEIRS Stone weirs are structures that span the stream and produce a drop in the water surface elevation. These structures are fre- quently made of angular quarried stone, but logs, sheet piling, concrete, boulders and masonry are also quite common. Well- constructed stone weirs can prevent or retard channel bed erosion and upstream progression of knickpoints and headcuts, as well as provide pool habitats for aquatic biota. Stone weirs or similar grade control structures are often intended to raise or elevate the bottom of incised channels, with the ultimate goal of elevating a dropping water table. Variations on stone weirs that have addi- tional habitat benefits are newbury rock riffles and cross vanes.

LONGITUDINAL STONE TOE A longitudinal stone toe (also known as longitudinal peaked stone toe protection [LPSTP]) is continuous bank protection consisting of a stone dike placed longitudinally at, or slightly streamward of, the toe of an eroding bank. The cross section of the stone toe is usually triangular in shape. The success of this method depends upon the ability of stone to self-adjust or "launch" into scour holes formed on the stream side of the revetment. The stone toe does not need to fol- low the bank toe exactly, but should be designed and placed to form an improved or "smoothed" alignment through the stream bend. Longitudinal stone toes usually require much less bank disturbance and the bank landward of the toe may be revegetated by planting or natural succession. Brushlayering and willow post and poles are excellent candidates for use with this technique. LONGITUDINAL STONE TOE WITH SPURS A longitudinal stone toe (also known as longitudinal peaked stone toe protection) has proven cost-effective in protecting lower banks and creating conditions leading to stabilization and reveg- etation of steep, caving banks. A large body of evidence indicates, however, that intermittent structures such as spurs tend to provide aquatic habitats superior to those adjacent to continuous struc- tures like a stone toe. This technique represents an effort to achieve erosion control benefits available from a continuous stone toe and habitat benefits associated with spurs. COCONUT FIBER ROLLS Coconut fiber rolls are manufactured, elongated cylindrical structures that are placed at the bottom of streambanks to help prevent scour and erosion. The coconut husk fibers (coir) are bound together with geotextile netting with 35 cm or 40 cm (12 in. or 18 in.) diameters and lengths of 6 m (20 ft). Coir is fairly long-lasting, typically 5 to 7 years, but must be designed with riparian revegetation to attain permanent solutions. Proper anchoring is critical and generally coir rolls are not recommended for areas with high velocities and shear. Brushlayering and live stakes are good candidates for combining with coconut fiber rolls. VEGETATED GABION BASKET Gabions are rectangular baskets made of twisted or welded- wire mesh that are filled with rock. These flexible and pervious structures can be used individually or stacked like building blocks to reinforce steep banks. Used alone, rock-filled gabions provide insufficient habitat benefit. However, woody vegetation, such as brushlayering or post and poles, can be incorporated by inserting the cuttings all the way through the basket during filling and pen- etrating the native subsoil. The woody vegetation can provide additional reinforcement and longevity to the structure while helping to mitigate loss of habitat. 31

32 LIVE CRIBWALLS A cribwall is a gravity retaining structure consisting of a hol- low, box-like interlocking arrangement of structural beams (for example, logs). The interior of the cribwall is filled with rock or soil. In conventional cribwalls, the structural members are fabri- cated from concrete, wood logs, and dimensioned timbers (usu- ally treated wood). In live cribwalls, the structural members are usually untreated log or timber members. The structure is filled with a suitable backfill material, and live branch cuttings are inserted through openings between logs at the front of the struc- ture and imbedded in the crib fill. These cuttings eventually root inside the fill and the growing roots gradually permeate and rein- force the fill within the structure. VEGETATED MECHANICALLY STABILIZED EARTH This technique consists of live cut branches (live brushlayer- ing) interspersed between lifts of soil wrapped in natural fabric, for example, coir, synthetic geotextiles (turf reinforcement mats [TRMs] or erosion control blankets [ECBs]), or geogrids. The fabric, branches and optional geogrids provide the primary geot- echnical reinforcement, similar to that of conventional mechani- cally stabilized earth, allowing relatively steep, stable slopes. The fabric wrap over the face of the soil lift prevents erosion until veg- etation takes over. The live, cut branches eventually root and leaf out, providing vegetative cover and secondary reinforcement as well. This technique is recommended for use above the annual high water stage. LIVE SILTATION Live siltation is a bioengineering technique involving the installation of a living or a nonliving brushy system at the water’s edge. Willow cuttings are the most common materials used. Live siltation construction is intended to increase rough- ness at the stream edge thereby encouraging deposition and reducing bank erosion. The embedded branches and roots also reinforce the bank and reduce geotechnical failure, while the branches and leaves provide cover, aquatic food sources, and organic matter. LIVE BRUSHLAYERING Live brushlayers are rows of live woody cuttings that are lay- ered, alternating with successive lifts of soil fill, to construct a reinforced slope or embankment. Vertical spacing depends on slope gradient and soil conditions. Live brushlayering provides enhanced geotechnical stability, improved soil drainage, and superior erosion control. It is one of the most effective ways to establish vegetation from live cuttings. Live brushlayering is an excellent candidate for combining with other streambank stabi- lization measures.

VEGETATED FLOODWAYS Confining floodwaters to a broad floodway bordered by levees or topographic highs is attractive because the portion of the flood- way not normally inundated can support vegetation and thus pro- vide wildlife habitat or recreational opportunities. Floodways may be created by constructing levees or floodwalls or by exca- vation. Excavation consists of creating terraces or benches along an existing channel or a completely new flood channel (bypass). Roadway embankments sometimes serve a dual purpose by defin- ing a floodway. MEANDER RESTORATION Meanders are broad, looping (sinuous) bends in a stream channel. Meandering is a form of slope adjustment with more sinuous channel paths leading to decreased reach gradient. Flu- vial and ecological functions are integrally related to the highly diverse spatial and temporal patterns of depth, velocity, bed material and cover found in meanders. Generally speaking, streams with natural meander bends do not require grade control measures. Meander restoration consists of reconstruct- ing meandering channels that have been straightened or altered by humans. BANK ARMOR AND PROTECTION VEGETATION ALONE Vegetation can be viewed as a living, organic groundcover consisting of grasses, legumes, forbs, or woody plants. Vege- tation is established on bare soils in order to help prevent surficial erosion, minimize shallow seated mass movement, provide habitat, and enhance aesthetics or visual appearance. Vegetation can be used alone under special circumstances, but it also lends itself well to conjunctive use with other erosion control techniques in a mutually beneficial manner. Living plants can be used in conjunction with nearly every type of groundcover. LIVE STAKING Live stakes are very useful as a revegetation technique, a soil reinforcement technique, and as a way to anchor erosion control materials. They are usually cut from the stem or branches of willow species, and the stakes are typically 0.5 to 1.0 m (1.5 to 3.3 ft) long. The portion of the stem in the soil will grow roots and the exposed portion will develop into a bushy riparian plant. This technique is referred to as Joint Planting when the stakes are inserted into or through riprap. Live staking is an excellent candidate for combination with other techniques. 33

34 WILLOW POSTS AND POLES Post and pole plantings are intended to provide mechanical bank protection. Willow and cottonwood species are recom- mended for their ability to root and grow, particularly if they are planted deep into the streambanks. Larger and longer than live stakes, posts and poles can provide better mechanical bank pro- tection during the period of plant establishment. Dense arrays of posts or poles can reduce velocities near the bank or bed surface, and long posts or poles reinforce banks against shallow mass fail- ures or bank slumps. Posts and poles are also excellent candidates for combination with other structural methods, for example, LWD structures, vegetated gabion baskets, live cribwall, and cross vanes. LIVE FASCINES Live fascines are bundles of live (and nonliving) branch cut- tings placed in long rows in shallow trenches across the slope on contour or at an angle. Fascines are intended to grow vegetatively while the terraces formed will trap sediment and detritus, pro- moting vegetative establishment. Fascines can be utilized as a resistive measure at the stream edge and for erosion control on long bank slopes above annual high water. Fascines are also an effective way to anchor ECBs and TRMs. TURF REINFORCEMENT MATS Turf reinforcement mats (TRMs) are similar to erosion control blankets, but they are more permanent, designed to resist shear and tractive forces; they are usually specified for banks subjected to flowing water. The mats are composed of ultraviolet (UV) sta- bilized polymeric fibers, filaments, or nettings, integrated together to form a three-dimensional matrix 5 to 20 mm (0.2 to 0.79 in.) thick. TRMs are a biotechnical practice intended to work with vegetation (roots and shoots) in mutually reinforcing manner. As such, vegetated TRMs can resist higher tractive forces than either vegetation or TRMs can alone. EROSION CONTROL BLANKETS Erosion control blankets (ECBs) are a temporary rolled ero- sion control product consisting of flexible nets or mats that can be brought to a site, rolled out, and fastened down on a slope. ECBs are typically manufactured of fibers such as straw, wood, excelsior, coconut, or a combination of these, and then stitched to or between geosynthetic or woven natural fiber netting. Various grades of biodegradable fibers and netting can be specified depending on required durability and environmental sensitivity.

GEOCELLULAR CONTAINMENT SYSTEMS Geocellular containment systems (GCS) are flexible, three- dimensional, high density polyethylene (HDPE), honeycomb- shaped, earth-retaining structures that can be expanded and backfilled with a variety of materials to mechanically stabilize surfaces. They can be used flat, as channel or slope lining, or stacked to form a retaining wall. GCS provide very little habitat enhancements alone, therefore these systems must be combined with vegetation to be considered environmentally sensitive. Live staking and joint planting are excellent choices for combining techniques. ROOTWAD REVETMENTS Rootwad revetments and tree revetments are structures constructed from interlocking tree materials. These structures are continuous and resistive, distinguishable from discontinu- ous and redirective techniques, such as LWD structures or rootwad deflectors. Rootwad revetments and tree revetments are primarily intended to resist erosive flows and are usually used on the outer bank of a meander bend when habitat diver- sity is desirable and tree materials are available and naturally occurring. LIVE BRUSH MATTRESS A live brush mattress is a thick blanket (15 to 30 cm [6 to 12 in.]) of live brushy cuttings and soil fill. The mattresses are usually constructed from live willow branches or other species that easily root from cuttings. Brush mattresses are used to simul- taneously revegetate and armor the bank. The dense layer of brush increases roughness, reducing velocities at the bank face, and protecting it from scour, while trapping sediment and pro- viding habitat directly along the water’s edge. Brush mattresses are an excellent candidate for combining with structural tech- niques such as rock toe protection. VEGETATED ARTICULATED CONCRETE BLOCKS An articulated concrete block (ACB) system consists of durable concrete blocks that are placed together to form a matrix overlay or armor layer. Articulated block systems are flexible and can conform to slight irregularities in slope topography caused by settlement. The blocks are placed on a filter course (typically a geofabric) to prevent washout of fines through the blocks. ACBs provide very little habitat enhancements alone, therefore these systems must be combined with vegetation to be considered envi- ronmentally sensitive. Vegetation in the form of live cuttings or grass plugs is inserted through openings in the blocks into the native soil beneath the blocks. 35

36 VEGETATED RIPRAP A vegitative riprap is a layer of stone and/or boulder armoring that is vegetated, optimally during construction, using pole plant- ing, brushlayering, and live-staking techniques. The goal of this method is to increase the stability of the bank, while simultane- ously establishing riparian growth within the rock and overhang- ing the water to provide shade, water quality benefits, and fish and wildlife habitat. Vegetative riprap combines the widely accepted, resistive, and continuous rock revetment techniques with deeply planted biotechnical techniques. SOIL AND GRASS COVERED RIPRAP Two configurations have been used: (1) an ordinary riprap blanket is covered with a layer of soil 30 to 60 cm (1 to 2 ft) thick from the top of the revetment down to base flow eleva- tion or (2) a crown cap of soil and plant material is placed over a riprap toe running along the base of a steep bank, effectively reducing the bank angle. Soils used for fill should not be highly erosive. A variety of methods may be used to establish plant materials, including hydroseeding, seeding and mulching, sod- ding, and incorporation of willow cuttings or root stock in the fill materials. VEGETATED GABION MATTRESS Gabion mattresses differ from gabion baskets as they are shal- low (0.5 to 1.5 m [20 to 60 in.] deep), rectangular containers made of welded wire mesh and filled with rock. Gabion mattresses are not stacked but placed directly and continuously on the prepared banks. They are intended to protect the bed or lower banks of a stream against erosion. A gabion mattress can be used as either a revetment to stabilize a streambank or, when used in a channel, to decrease the effects of scour. Live cuttings are introduced through the rock filled mattress and inserted into native soil beneath. COBBLE OR GRAVEL ARMORS Cobble or gravel armor is a resistive technique, similar to riprap revetment, that uses naturally occurring rock. Cobbles are natural stones larger than 6.5 cm (2.5 in.) in diameter that have been rounded by the abrasive action of flowing water, while gravel is material smaller than cobble, but larger than sand (larger than about 5 mm [0.2 in.]). Rounded river cobble or gravel blanket presents a more natural appearance and can be as effective as riprap revetment for areas with relatively lower tractive forces and velocities.

TRENCH FILL REVETMENT Trench fill revetments are constructed by excavating a trench along the top of the bank and placing stone riprap in the trench. As the bank erodes, the stone is undercut and “launches” down the bank line, resulting in a more gradual, protected slope. Earth removed for excavation of the trench may be used to cover the riprap, thus completely concealing it until it is launched. This technique might be chosen if access to the stream reach is restricted due to legal or environmental issues. RIPARIAN BUFFER AND STREAM OPPORTUNITIES LIVE GULLY REPAIR Live gully fill repair consists of alternating layers of live branch cuttings and compacted soil. This reinforced fill can be used to repair small gullies. The method is similar to branch packing (a method for filling small holes and depressions in a slope), but is more suitable for filling and repairing elongated voids in a slope, such as gullies. Gully treatment must include correcting or elim- inating the initial cause of the gully as well as the gully itself. Gul- lies are likely to have tributary gullies that also require treatment. VANES WITH J-HOOKS Vanes with J-hooks are actually rock vanes modified to enhance the instream habitat benefits. They are redirective, upstream-pointing deflection structures whose tip is placed in a “J” configuration and partially embedded in the streambed so that it is submerged even during low flows. The rock vanes have demonstrated effectiveness in reducing near-bank velocities by redirecting the thalweg toward the center of the channel. The “J” structures are intended to create scour pools and thereby improve substrate complexity. The scour usually results in a “tail out” deposition of gravel (riffle) which may provide spawning habitat. CROSS VANES Cross vanes (also known as vortex weirs) are “V” shaped, upstream-pointing, rock structures stretching across the width of the stream. Cross vanes redirect water away from the streambanks and into the center of the channel. This serves to decrease shear stress on unstable banks, as well as create aquatic habitat in the scour pools formed by the redirected flow. Cross vanes are designed to be overtopped at all flows. The lowest part of the structure is the vortex of the “V,” which is at the point farthest upstream. The crests are sloped 3% to 5% with the ends of the vanes keyed into the streambanks at an elevation approximate to annual high water or bankfull stage. This shape forms a scour pool inside the “V.” Cross vanes are particularly useful for mod- ifying flow patterns, enhancing in-stream habitat and substrate complexity, and providing in-grade control. Double cross vanes (W weirs) are a variation suitable for wider channels. 37

38 BOULDER CLUSTERS Large boulders may be placed in various patterned clusters within the base flow channel of a perennial stream. Natural streams with beds coarser than gravel often feature large rough- ness elements like boulders that provide hiding cover and velocity shelters for fish and other aquatic organisms. If a con- structed or modified channel lacks such features, adding boul- der clusters may be an effective and simple way to improve aquatic habitat. NEWBURY ROCK RIFFLES Newbury rock riffles are ramps or low weirs with long aprons made from riprap or small boulders that are constructed at inter- vals along a channel approaching natural riffle spacing (5 to 7 channel widths). The structures are built by placing rock fill within an existing channel. The upstream slope of the rock fill is typically much steeper than the downstream slope, which creates a longitudinal profile quite similar to natural riffles. These struc- tures provide limited grade control, pool and riffle habitat, and visual diversity in otherwise uniform channels. SLOPE STABILIZATION DIVERSION DIKE A diversion dike is a low berm (or ditch and berm combi- nation) that is constructed along the crest or top of a stream- bank. The purpose of a diversion is to intercept and divert concentrated runoff away from the face of a steep slope or streambank. Diversion dikes are constructed from compacted earthen fill and should be used on drainage areas of 2 ha (5 ac) or less. In addition to protecting the face of a streambank from overbank runoff, diversions may also improve general slope stability by preventing runoff from infiltrating into and satu- rating the bank. SLOPE DRAIN A slope drain is a drainage system used to collect and transport storm runoff down the face of a slope. This system usually con- sists of a berm at the top of the slope or streambank and a flexi- ble pipe with end sections and outlet protection. A pipe slope drain is constructed with corrugated pipes (polymeric or metallic) and can be temporary or permanent. Slope drains are commonly used to: (1) temporarily convey runoff down the face of a steep slope until permanent protection or cover can be established, (2) prevent further cutting of a gully, and (3) serve as a permanent drainage-way down a steep slope where visual appearance is not a factor.

LIVE POLE DRAINS Live pole drains are live, growing, and often long-lived drainage systems composed of bundles (fascines) of live branches (commonly willow). Live pole drains are placed in areas where excess soil moisture results in soil instability. They are also used to treat small drainage gullies. Live pole drains collect subsurface drainage and concentrated surface flow and channel them to the base of the bank. Once established, their drainage function is increased, as the plants absorb much of the water that is con- ducted along their stems. Because they are long and fibrous, the bundles act like a conduit. As the fascines begin to root and sprout, the root system acts like a filter medium, stabilizing fine particles and reducing piping and sapping. Live pole drains provide drainage and stabilization immediately after installation and, once estab- lished, produce roots that further stabilize bank and levee slopes. CHIMNEY DRAIN A chimney drain is a subsurface drainage course placed between a natural slope or streambank and an earthen buttress fill or other retaining structure (for example, log crib wall). A drainage blanket, sloped sheet drain, and strip drain are types of subsurface drainage courses. Typically, a chimney drain is a near- vertical drain that feeds into a collection system at its base, whereas a sloped sheet drain is inclined back at an angle. A sub- surface drain may be continuous across the slope, or it may con- sist of discontinuous drainage strips that are placed against the natural slope at periodic intervals. TRENCH DRAIN A trench drain is a drainage trench excavated parallel to and just behind the crest of a streambank. Ideally, the bottom of the trench should be keyed into an impermeable layer in the slope. The trench should be backfilled with a coarse graded aggregate that meets filtration criteria; that is, it should allow unimpeded flow of groundwater while excluding fines. Alternatively, the trench can first be lined with a filter fabric that meets the filtration requirements and then be backfilled with a coarse aggregate. The purpose of the trench is to intercept and divert shallow seepage away from the face of the streambank. DROP INLET Concentrated overbank runoff can be a major cause of erosion, especially along deeply incised channels. Runoff passing over the top of banks frequently triggers gully development and expan- sion. Water that is ponded at the top of high, steep banks and infiltrates or seeps into the ground behind the slope face is often a major factor in erosion by piping or slope failure. Gully erosion and downcutting can be addressed using a drop inlet, which is a water control structure that consists of an L-shaped corrugated pipe passing through an earthen embankment placed at the down- stream end of the gully. 39

40 FASCINES WITH SUBSURFACE INTERCEPTOR DRAIN Rows of drainage fascines (also known as live pole drains) are installed off contour along a slope. Drainage fascines are widely used to help dewater landslides or small gullies and on very wet sites where there is evidence of substantial subsurface seepage that is causing piping and slope instability. As the seepage and drainage become concentrated, the fascines can be connected to a subsurface drain, consisting of a perforated pipe wrapped in a geocomposite drainage medium, and placed at the bottom of a trench. The trench is backfilled with clean, coarse aggregate or gravel that is oriented downslope. There is significant evidence that live drainage fascines, usually constructed from willow cut- tings, are long lived once established. SLOPE FLATTENING Flattening or bank reshaping stabilizes an eroding streambank by reducing its slope angle or gradient. Slope flattening is usually done in conjunction with other bank-protection treatments— including installation of toe protection, placement of bank armor, revegetation, and erosion control—or installation of drainage measures. Flattening or gradient reduction can be accomplished in several ways: (1) by removal of material near the crest, (2) by adding soil or fill at the bottom, or (3) by placing a toe structure at the bottom and adding a sloping fill behind it. Right-of-way constraints may limit or preclude the first two alternatives because both entail either moving the crest back or extending the toe forward. STONE-FILL TRENCHES Stone-fill trenches are rock-filled trenches placed at the base of a streambank, usually within a failed section of the toe. A series of trenches are excavated at or within the toe of the slope in a direction perpendicular to the stream. The trenches are backfilled with crushed rock or stone. The toe of the slope is then recon- structed by placing and compacting earthen fill within and atop the stone-fill trenches. A small, longitudinal riverside plug or stone dike should be used between the stone trenches to help con- tain and protect the toe of the earthen fill placed between and atop the stone trenches.