ADVANTAGES
Establishes vegetative cover and root mat, reduces flow velocities on vegetative surface, traps sediment laden runoff, aesthetically pleasing once established, grows stronger with time as root structure develops, usually has deeper root structure than grass.
LIMITATIONS
Expensive, may be labour intensive to install, not commonly used in Alberta highway construction projects, revegetated areas are subject to erosion until plants are established, plants may be damaged by wildlife, watering is usually required until plants are established.
ADVANTAGES
Provide immediate soil stability and habitat Can be used with other toe protection such as, rootwads, coir rolls, and log toes. Combining live brushlayering with rock toes is an effective and relatively low cost technique for revegetating and stabilizing streambanks. Provides a source of shade and nutrients, while slowing velocities along the bank during flooding flows. They provide a flexible strengthening system to fill slopes. Act as horizontal drains and favourably modify the soil water flow regime.
LIMITATIONS
Live cuttings are most effective when implemented during the dormancy period of chosen plant species. Brushlayers are vulnerable to failure before rooting occurs, and they are not effective at counteracting failure along very deep-seated failure planes.
ADVANTAGES
Provides a dense network of branches that quickly stabilize a slope or streambank. Will trap sediments during high water and eventual plant growth will enhance aquatic habitat. Well suited for combined installation with many other streambank or slope stabilization techniques such as Vegetated Riprap, Live Stakes, Live Fascines, Rootwad Revetment, Live Siltation, and Coconut Fibre Rolls. Provides immediate surface protection against floods, greatly reducing water velocity at the soil surface. Cuttings are usually available locally. Relatively economical technique. Captures sediment during floods, assisting in rebuilding of bank. Produces riparian vegetation rapidly and enhances wildlife habitat value.
LIMITATIONS
Does not show high success on streams where basal ends cannot be kept wet for the duration of the growing season. They should be installed during the dormant season for woody vegetation and Installation is labour intensive.
ADVANTAGES
A very effective and simple conservation method using local plantmaterials. Can be constructed in combination with rock toes, Rootwad Revetments, Coconut Fibre Rolls, Live Fascines, and Brush Mattresses. Valuable for providing immediate cover and fish habitat while other revegetation plantings become established. The protruding branches provide roughness, slow velocities, and encourage deposition of sediment. The depositional areas are then available for natural recruitment of native riparian vegetation.
LIMITATIONS
If using a living system, cuttings must be taken during the dormancy period.
ADVANTAGES
Willow posts and poles are inexpensive to acquire, install, and maintain, provide longterm protection. They may be inserted into stone or soil backfill and thus become incorporated with the structure as they root. They can also be incorporated into many techniques during construction (e.g., Vegetated Riprap, Vegetated Gabions), and can be planted in the keyways of many structures. Aquatic and terrestrial habitat is provided and/or improved. Willows act as pioneer species, and allow other plant species to colonize the area after the willows have become established.
LIMITATIONS
Willow posts and poles have higher survival rates when planted during their dormant season, so planning should be adjusted accordingly. Optimum stabilization is not achieved until the willows become established, typically at least one season after installation, although they provide some reinforcement immediately following installation.
ADVANTAGES
Rock vanes can successfully reduce near-bank velocities and shear stress, vegetation establishment is greatly improved. Vanes are often combined with other biotechnical soil stabilization measures for bank areas between the vanes. Provide aquatic habitats superior to resistive, continuous structures like Riprap and Longitudinal Stone Toe. Controlled scour at the vane tip, the creation of pool/riffle bed complexity, and increased deposition of the upstream end are the major environmental benefits of vanes. Vanes provide fish rearing and benthic habitat, creates or maintains pool and riffle habitat, provides cover and areas for adult fish, and velocity refugia. The redirection of impinging flows away from the bank and the sedimentation on the upstream side of the vane creates areas where vegetation can effectively re-establish. Areas of active bank erosion become depositional, vegetate, and subsequently, become permanently stable. The technique is appropriate under a range of flow conditions and bed materials and can be used in series to redirect flows around bends. Vane installation does not require extensive bank reshaping, and most heavy equipment work can be done from the top of the bank, further reducing site disturbance. Vanes require less rock and heavy equipment than riprap for a similar length of protected bank.
LIMITATIONS
Unintended impacts can result from improper design and construction. If the vane is not properly keyed into the bank, it is likely to fail, creating new localized erosion problems. Improper vane angle and crest elevation can redirect flow in unintended directions, triggering downstream erosion.
ADVANTAGES
Willow posts and poles may be incorporated into key sections and used to revegetate the middle and upper bank above stone toe. May be combined with a number of other different techniques and the results enhance aquatic habitats. Longitudinal Stone Toe with Spurs is a variation on this technique. Bank grading, reshaping, or sloping is usually not needed (existing bank and overbank vegetation need not be disturbed or cleared), nor is a filter cloth or gravel filter needed. If stone is placed from the water side, existing bank vegetation need not be disturbed. It is very cost-effective and is relatively easy to design, specify and construct. It is easily combined with other bank stability techniques that provide superior habitat compared to pure riprap.
LIMITATIONS
Only provides toe protection and does not protect mid- and upper bank areas. Some erosion of these areas should be anticipated during longduration, high energy flows, or until the areas become otherwise protected. Stone toe is not suitable for reaches where rapid bed degradation (lowering) is likely, or where scour depths adjacent to the toe will be greater than the height of the toe.
ADVANTAGES
The presence of vegetation softens the stark visual appearance of conventional mechanically stabilized earth structures and provides potential habitat for riparian wildlife. Overhanging branches of the live brushlayers provide shade for fish and a substrate for insects and other organisms that the fish feed upon. They permit much steeper slopes to be constructed than would be possible with live brushlayers alone. Brushlayering treatment by itself is normally restricted to slopes no steeper than 1V:2H. VMSE can be constructed with a slope as steep as 1V:0.5H. The vegetation shields the fabric against damaging UV radiation, and provides visual and riparian habitat benefits. The brushlayers act as horizontal drains that favourably modify the groundwater regime in the vicinity of the slope face, thereby improving stability against mass slope failure.
LIMITATIONS
A VMSE structure must be constructed during the dormancy period to insure good vegetative propagation and establishment. Alternatively, the live cuttings may be harvested during dormancy, and placed in temporary cold storage until they are ready for use during an out-of-dormancy period, viz., during the summer months (increases the cost). Materials procurement is more demanding, and installation more complex, because of the blending of two distinct methods, viz., conventional MSE and live brushlayering, into a single approach. Costs will also be more than brushlayering used alone, because of the added expense of the geotextile and the additional labour required to handle and construct the wraps. VMSE streambank structures must be constructed during periods of low water because of the need to excavate and backfill a trench with rock in the streambed to provide a stable foundation.
ADVANTAGES
When graded or “self-launching” stone are used, riprap is self-adjusting to small amounts of substrate consolidation or movement. The revetment can sustain minor damage and still continue to function adequately without further damage. The rough surface of the riprap dissipates local currents and minimizes wave action more than a smooth revetment (like concrete blocks). Stones are readily available in most locations, and materials are less expensive than many other “hard armouring” techniques. The rock provides a large amount of aquatic habitat it’s easily repaired. The fibrous roots of the chosen vegetation prevents washout of fines, stabilizes the native soil, anchors armour stone to the bank, and increases the lift-off resistance. The vegetation also improves drainage of the slope by removing soil moisture for its own use. Vegetated riprap has a more natural appearance, and is therefore more aesthetically pleasing, which is frequently a matter of great importance in high-visibility areas. The vegetation also supplies the river with carbon-based debris, which is integral to many aquatic food webs, and birds that catch fish or aquatic insects will be attracted by the increased perching space next to the stream. The brushlayering methods reach out over the water, and provide shade and organic debris to the aquatic system.
LIMITATIONS
Vegetated riprap may be inappropriate if flow capacity is an issue, as bank vegetation can reduce flow capacity, especially when in full leaf along a narrow channel. In remote areas large rocks may be difficult to obtain and transport, which may greatly increase costs. Riprap may present a barrier to animals trying to access the stream.
ADVANTAGES
Durable with high tensile strength. Rolls and Mats accumulate sediment while plants grow and roots develop. Biodegradable. Can be combined with brushlayering to provide immediate shoreline or streambank protection.
LIMITATIONS
Coir Rolls are relatively expensive. Technique should be implemented during the dormancy period of the cuttings used for brushlayering and staking.
