Vegetated armoring erosion control
The purpose of using vegetated armoring shore protection techniques in controlling waterward erosion is to combine the structural integrity of technical shore protection with the positive biological aspects associated with biological shore protection. Vegetated armoring techniques integrate biological and technical methods. Providing woody cover and vegetation is key in preserving and/or establishing critical habitat for shoreline inhabitants regardless of the biotechnical shore protection technique.
Vegetated armoring structures mimic the natural environments through the use of woody and vegetative elements in the biotechnical techniques. In addition to vegetation is the special importance of dead materials that substitute for woody cover that is typically lost during the construction of shore protection. Dead trees and woody debris provide a significant amount of food and cover for a wide variety of animals. Further, the use of natural products in biotechnical shore protection promotes faster and often better establishment of natural vegetative cover. The incorporation of inert materials (typically rock) increases substrate size, increases interstitial habitats for invertebrates and fishes. However, in comparison to biological techniques, the tradeoff is slower and possibly less recovery or establishment of nearshore vegetation along the water’s edge.
Geomorphic characteristics such as bank geometry play a major part in the employment of bioengineering. The angle required varies with the soil, equipment used and several other factors. Sand, for instance, has an angle of repose of about 30 degrees, whereas clay can stand on a much steeper angle. Most slopes that accommodate revegetation are less than 1-1.5 V:1 H. On steep banks where undercutting may be a problem, the toe of the bank may need protecting with riprap or other hard, structural treatments. Control of shoreline erosion can be achieved with soil bioengineering techniques provided the energy of the waves does not exceed the resistance of the plant roots or combination of plant roots and manufactured systems.
Additionally, roots add tensile strength, binding together masses of stone and soil. Stems and branches dissipate wave energy, shielding the soil from the erosive force—growing vegetation sprouts to fill in any open, eroding areas. As a supplement to structural wings, live woody cuttings have the advantage of extending roots and sprouts that protect and bind masses of soil. Additionally, as vegetated systems grow, they become increasingly effective in preventing shoreline erosion.
Integrated toe protection
Biotechnical integrated toe protection designs have toes made of inert materials, including rock and armor units. The bank above the OHWM may incorporate inert materials if necessary into the particular selected design.
One crucial aspect of integrated toe protection is the establishment of the hard toe, made of rock and filter cloth. In most instances, this will provide scour protection for the vegetative material located above the toe. When establishing any type of integrated to protection technique, the specifications for individual sites will depend on the amount of wave action and scour activity. Rocks should be lined below the water level at the deepest scour depth over a layer of 3-inch filter cloth and gravel or a 6-inch layer of gravel only. This will prevent the most destructive wave from reaching the biological shore protection placed above.
These are techniques that incorporate vegetation into the joints of placed rock into stone riprap. A “stinger,” that is a long metal probe mounted on a backhoe, used to create a pilot hole in the joints of riprap for inserting a long and living willow or cottonwood post. Vegetated riprap is an example where standard riprap methods are used; however, plants are inserted between the rock spaces to provide a vegetative covering. This combining of biological and technical shore protection techniques allows excellent waterside erosion protection with natural scenic beauty similar to biological shore protection.