Erosion is a natural process that rivers undergo as they meander, or move back and forth across their floodplain. However, clearing of land, building structures that permanently alter the river’s course, and removing trees and shrubs whose roots help stabilize the banks of the river all increase the rate at which the slopes deteriorate. Sediment is then released into the water, which decreases water quality, and the removal of the tree canopy results in warmer water. There are many ways to reduce erosion, but a common natural method is to re-introduce native species.
The NWAI tree nursery was developed to support active reforestation and riverbank stabilization projects along the Nashwaak River and, in particular, to provide healthy trees for the Nashwaak Greenway project. Starting in 2016, NWAI increased its production of Silver Maple (Acer saccarinum) so that by 2018 at least 1,000 three-year old trees will be ready annually for planting along disturbed sections of floodplains and eroded river banks of the Nashwaak in order to re-establish this critical habitat that these forests provide to sensitive and species at risk.
Landowners in the watershed are encouraged to participate in shoreline naturalization. Free site visits are available to waterfront property owners. During these visits staff will provide advice and recommendations for the property then create and implement a planting plan. Two successful shoreline plantings on private properties can be viewed in the videos below:
Floodplain forests are critically important ecosystems. One of the main benefits they offer to the river is their ability to mitigate flood damage by absorbing large amounts of water and slowing the speed and reducing the height of a flood. Planting Silver Maples can significantly reduce soil runoff and erosion along a riverbank. A mature Silver Maple can draw up and release into the atmosphere 200 L of water every hour (Kozlowski and Davies, 1975). In addition, their canopy shades the river and helps to moderate its temperature. Riparian forests (those along the banks of a river) provide habitat for many different species of animals and plants. For these reasons, NWAI is committed to restoring the Silver Maple floodplain forest communities along the banks of the Nashwaak River.
In areas of more severe erosion, NWAI advocates the use of bio-engineering methods, including geotextile fabric, which biodegrades after several years. This method is not only much cheaper than rip-rap (rocking the entire bank), but looks more natural and provides riparian habitat while shading the adjacent stream. In 2017, NWAI completed 2 bioengineered bank restorations: one in Marysville and one on MacPherson Brook.