Agenda - Environmental Policy Board - 04/18/2016

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5 Bioengineering approaches combine engineering techniques with ecological principles to stabilize the bank. They rely heavily on deep-rooted native plants along with a variety of other natural materials to reinforce and stabilize eroding riverbanks. Bioengineering also incorporates the goals of fish and wildlife habitat restoration, maintenance of water quality, and aesthetic considerations. In addition to bank stabilization, many benefits are achieved through bioengineering: • Improved aquatic and terrestrial habitat, • Increased connectivity among habitats along the riverbank, • Decreased water temperatures through shading, and • Improved soil and water quality. The stabilization solution for an eroding riverbank could certainly use a combination of hard armoring and bioengineering. In fact, ACD often recommends this combination on large river systems such as the Mississippi River because of the benefits provided by both approaches. Possible Stabilization Approaches Stabilization of riverbanks can be achieved through many different approaches. Below is a list of some common stabilization approaches (both bioengineering and hard armoring) to correct erosion issues. Again, a combination of approaches is often specified as the most effective solution. • Restoration of Native Vegetation — Deep-rooted, native vegetation creates a buffer along the riverbank that can provide stabilization and minimize erosion. Furthermore, if the bank is damaged, the vegetation has the ability to self - heal with additional growth. • Cedar Tree Revetment — Anchoring Eastern Red Cedar trees to the toe of the slope reduces water velocities near the bank to protect against erosion. Furthermore, the reduced water velocities promote sedimentation and can actually help rebuild the bank. This provides a cost-effective bioengineering option for moderate to severely eroding riverbanks. • Live Staking — Dormant, live stakes of native species (e.g. Sandbar Willow) can be installed to establish a dense plant community with high stem density that will stabilize the riverbank. • Hard Armoring — Hard armoring of the bank may be necessary along riverbanks on large systems that experience the greatest erosive forces (e.g. outside bends). However, it is often not necessary to hard armor the entire bank from the toe of the slope to the top of the bank. Rather, the hard armoring can extend to a predetermined elevation (e.g. 2-year or 5-year flood elevation), above which could be stabilized using the establishment of native vegetation. Furthermore, the sections that are hard armored can often be live staked to provide additional stabilization value, wildlife habitat, and improved shoreline aesthetics.