by Alana Coulombe
Developed shorelines have a higher risk of erosion and often require protection of upland areas. The best way to stabilize your shoreline for long-term protection is by enhancing or creating a natural shoreline buffer consisting of native wildflowers, trees, shrubs, and grasses. If, however, your shoreline requires a stronger approach than plants alone, consider installing vegetated riprap instead of typical retaining walls or gabion baskets (Natural Edge, 2022). Riprap uses natural stone/rock placed on a gentle 3:1 angled slope to absorb wave energy on the shoreline (Natural Edge, 2022). To mitigate the issue of traditional riprap not providing sufficient wildlife and fish habitat within the riparian zone, rocks can be combined with native vegetation to provide greater erosion control and habitat preservation (Tron & Raymond, 2014).
Vegetated riprap is both aesthetically pleasing and environmentally friendly for water bodies needing continuous and resistive bank protection (Alberta Environment and Sustainable Resource Development [ESRD], 2011). Vegetated riprap is especially effective against high water, aggressive water flow, and ice movement (Otty Lake Association, 2017). Vegetated riprap offers the immediate and long-term protection afforded by traditional riprap as well as habitat benefits from the creation of a healthy riparian buffer (ESRD, 2011).
From an economic perspective, rocks are less expensive and more readily available than materials used in many other hardening techniques (ESRD, 2011). Since riprap consists of many small rocks, the overall structure is not compromised by the movement of a few rocks or shifts in the shoreline or bottom soil (Otty Lake Association, 2017). Therefore, riprap has the ability to self-adjust and, if needed, can be easily repaired by adding more rock (ESRD, 2011). The use of rough, angular-shaped rock is preferred over smooth, rounded stone because rough rocks can interlock and better resist overturning. Riprap design should consider the source of the rock in relation to sediment introduction as well as the size, type, and configuration of the rock with regard to its hydraulic relationship. Rock is an ecologically favourable material to use over other hardening materials such as concrete or steel because the rough substrate is available for invertebrates to colonize and can enhance aquatic habitat (ESRD, 2011).
When native vegetation is included in the riprap structure, the root systems lock the rocks in place preventing damage to the riprap and improving the riprap’s resiliency (Natural Edge, 2022). Additionally, deep-rooted vegetation, like trees and shrubs, can bind and stabilize the soil along your shoreline, reducing the risk of property loss caused by erosion (Natural Edge, 2020). Using their extensive root systems, these plants will act as barriers to reduce surface runoff, slow floodwaters, and filter pollutants and excess nutrients, thus improving water quality (Natural Edge, 2022). Plants also improve drainage of the slope by removing water from the soil through uptake and transpiration (ESRD, 2011).
In addition to shoreline protection, native vegetation is a vital part of the aquatic and terrestrial ecosystems and improves the aesthetic value and natural appearance of the shoreline property (ESRD, 2011). Overhanging branches and vegetation also provide cover, shade to cool the water, organic debris, food sources like insects, an easy transition from land to water, and other crucial habitat features for fish, frogs, turtles, waterfowl, and other wildlife (Natural Edge, 2020). To soften existing riprap, plant native vegetation behind the riprap and above or between the rocks, moving rocks if necessary to create space (Otty Lake Association, 2017).
To study the effects of vegetation on riprap stability, an analysis was conducted on the vegetated riprap installation along the Columbia River riverbank in British Columbia in 2013 (Tron & Raymond, 2014). While investigating the root system development within the vegetated riprap, it was determined that the additional root cohesion was more effective in the deeper soil layer predominated by the soil matrix (Tron & Raymond, 2014). Additionally, the roots did not increase the cohesion in the upper soil layer, which contains a larger particle size, but rather acted as a network to tie the rocks of the riprap together (Tron & Raymond, 2014).
Vegetated riprap is a biotechnical stabilization technique that combines structural and vegetative elements together in an integrated manner (ESRD, 2011). The rough surfaces of the rocks help to minimize wave action while plantings between the rocks and behind the riprap facilitate the erosion control and create wildlife habitat (Natural Edge, 2022). If an engineer has advised you that creating a natural shoreline buffer is not a strong enough approach for your shoreline property, consider installing vegetated riprap for long-term shoreline protection against erosion. Ensure the qualified engineers or contractors installing your vegetated riprap take all necessary precautions to protect your shoreline and the waterbody during construction (Natural Edge, 2022). This includes the responsible use of heavy equipment to prevent interference with existing vegetation and habitat as well as proper sediment barriers to prevent water quality issues and damage to fish and wildlife populations (Natural Edge, 2022). Please note the need for permits for work in or near water and the governing body responsible for those permits varies from region to region. Be sure to check with your local municipality, conservation authority (if applicable), appropriate provincial ministry and/or appropriate federal department for the permits to do work in or around water.
Alberta Environment and Sustainable Resource Development. (2011). Lake Shoreline Stabilization Techniques. Government of Alberta. https://www.parklandcounty.com/en/live-and-play/resources/Documents/PRC/iceheave/Shoreline-Stabilization-Sample-Plans.pdf
Natural Edge (2020). Shoreline habitat creation manual. Watersheds Canada. https://watersheds.ca/habitat-creation-manual-download/
Natural Edge (2022). Guide to building resilient shorelines. Watersheds Canada. https://watersheds.ca/download-building-resilient-shorelines-guide/
Otty Lake Association. (2017). Otty Lake Shoreline Handbook. https://www.ottylakeassociation.ca/documents/otty_lake_shoreline_handbook.pdf
Tron, S., & Raymond, P. (2014). Analysis of root reinforcement of vegetated riprap. EGU General Assembly Conference Abstracts, 16(4928). https://ui.adsabs.harvard.edu/abs/2014EGUGA..16.4928T
This blog is part of a five-part series generously funded under the Great Lakes Protection Initiative – Areas of Concern (AOC) Program by Environment and Climate Change Canada. This three-year project will support important shoreline restoration in the St. Lawrence River AOC through the Natural Edge Program, and is being delivered by Watersheds Canada, Mohawk Council of Akwesasne, River Institute, Great River Network, and Raisin Region Conservation Authority.