by Alana Coloumbe, Education programs administrator
Shorelines are the interface between land and bodies of water that are important for both humans and wildlife. Shorelines facilitate the exchange of resources between aquatic and terrestrial ecosystems, and therefore affect the functioning and ecological condition of both ecosystems (Wensink & Tiegs, 2016).
Recent human developments for industrial, commercial, recreational, and residential purposes have threatened shoreline stability across Canada. Developed shorelines may have a large dock or deck, a straight path from a building to the shore, multiple large paved surfaces, a manicured lawn right to the water’s edge, and little to no upland forest, shoreline vegetation, or aquatic vegetation. These features result in an inability to manage stormwater and thus, increased surface runoff which can lead to greater flooding and erosion, as well as declining water quality.
Developed shorelines in the fall (Getty Images Signature).
What are hardened and soft shorelines?
To protect upland areas and developments, many shorelines are stabilized using hardened shoreline engineering to prevent flooding and erosion (Hartig et al., 2011). Hardened shorelines contain structures such as retaining walls made of concrete, steel, armour stone, gabion baskets, or wood. Although hardened shorelines can provide some short-term benefits for humans, they can have severe ecological and economic impacts. For example, hardened shorelines can impact water quality, have detrimental effects on nearby ecosystems, and increase erosion along a shoreline resulting in property loss (Bilkovic et al., 2016).
A more sustainable alternative to hardened shorelines is the engineering of soft shorelines. Soft shorelines utilize habitat restoration alone or together with some type of built infrastructure for shoreline protection (Smith et al., 2020). Soft shorelines consist mainly of native vegetation with the possible addition of stones, woody debris, and other structural or organic materials (Bilkovic et al., 2016). By enhancing or creating a natural shoreline buffer, soft shorelines provide long-term flood and erosion protection while also improving habitat and water quality (Bilkovic et al., 2016).
A blend of both: vegetated riprap.
What problems are associated with hardened shorelines?
Humans share the critical land-water interfaces created by shorelines with a variety of wildlife including native plants, fish, birds, and amphibians. However, hardened shorelines can disturb and eliminate habitats, reduce habitat connectivity, affect species distributions, and facilitate invasive species (Dugan et al., 2018). For instance, hard stabilization structures placed beyond the original waterline remove shallow-water habitat (Wensink & Tiegs, 2016). Likewise, retaining walls create a sharp, vertical division instead of a gradual, sloping transition into the water, thus eliminating the dynamic ability of natural shorelines to move with fluctuating water levels (Wensink & Tiegs, 2016). As a result, these spatially fixed shorelines foster habitats that are either permanently terrestrial or permanently aquatic (Wensink & Tiegs, 2016).
Additionally, hardened shorelines alter hydrodynamics, thus changing the water flow and transport of sediments (Dugan et al., 2018). By reflecting wave energy and restricting natural shoreline dynamics, hardened shorelines can cause flanking erosion of adjacent shorelines resulting in property loss and reduced water clarity (Dugan et al., 2018). In comparison to soft shorelines, hardened shorelines also contain larger sediment sizes and accumulate less lake-derived wrack despite showing slower decomposition of organic matter (Wensink & Tiegs, 2016). In addition to their ecological harm, hardened shorelines can be expensive and high maintenance while offering little aesthetic value (Smith et al., 2020).
Rushing water during a heavy rain event carries sediments, pollution, and warmth over a developed property into the lake.
Why are soft shorelines preferred?
Soft shorelines provide numerous long-term ecological and economic benefits, and they are beautiful! Soft shorelines create diverse habitats and maintain healthy ecosystems that support the success of native wildlife (Bilkovic et al., 2016). Through their dynamic nature, soft shorelines enhance habitat connectivity to ensure wildlife and organic matter can move freely between terrestrial and aquatic habitats and along the shoreline (Bilkovic et al., 2016). Furthermore, a natural shoreline, consisting of native species of wildflowers, trees, grasses, and shrubs, acts as a shoreline buffer to help reduce runoff by slowing surface water so it can reach the soil for proper filtration. By filtering rainwater, sequestering carbon, and cycling nutrients, soft shorelines reduce the amount of pollution and excess nutrients entering the freshwater body, keeping it safe and healthy (Smith et al., 2020).
The various root structures of the native vegetation also work to bind the soil in place along the shoreline and absorb and redistribute water to reduce erosion and flooding. In particular, trees and shrubs transpire water from the soil to the air, aiding in flood recovery by drying the property out faster. Therefore, soft shorelines promote resilience to storms and water level rises by acting as natural barriers to slow rising floodwaters and stormwater runoff (Bilkovic et al., 2016). Waterfront property owners interested in naturalizing and restoring their shoreline can access free resources and planting opportunities through Watersheds Canada’s national program, The Natural Edge.
The beginnings of a native plant buffer that works with stone and large woody debris to protect the shoreline from erosion.
Soft shorelines can additionally stabilize sediments and attenuate waves (Smith et al., 2020). By these means, soft shorelines reduce erosion, thereby promoting the long-term stabilization and safety of the shoreline while improving its aesthetic value and maintaining water clarity (Hartig et al., 2011). As a means of long-term shoreline protection and enhancement, soft shorelines require less maintenance and are more cost effective than hardened shoreline infrastructure (Smith et al., 2020).
So, is softening your shoreline property really the “soft” choice? Now that we know the ecological and economic benefits (and beauty!) of soft shorelines, we can challenge the misconception that natural shorelines are inferior to hardened infrastructure for shoreline protection. Will you break the status quo and soften your shoreline for greater shoreline stability and habitat enhancement, and to improve the health and biodiversity of your freshwater and terrestrial ecosystems overall?
References
Bilkovic, D. M., Mitchell, M., Mason, P. A., & Duhring, K. (2016). The role of living shorelines as estuarine habitat conservation strategies. Coastal Management, 44(3), 161–174. https://doi.org/10.1080/08920753.2016.1160201
Dugan, J. E., Emery, K. A., Alber, M., Alexander, C. R., Byers, J. E., Gehman, A. M., McLenaghan, N., & Sojka, S. E. (2018). Generalizing ecological effects of shoreline armoring across soft sediment environments. Estuaries and Coasts, 41, 180–196. https://doi.org/10.1007/s12237-017-0254-x
Hartig, J. H., Zarull, M. A., & Cook, A. (2011). Soft shoreline engineering survey of ecological effectiveness. Ecological Engineering, 37(8), 1231–1238. https://doi.org/10.1016/j.ecoleng.2011.02.006
Smith, C. S., Rudd, M. E., Gittman, R. K., Melvin, E. C., Patterson, V. S., Renzi, J. J., Wellman, E. H., & Silliman, B. R. (2020). Coming to terms with living shorelines: A scoping review of novel restoration strategies for shoreline protection. Frontiers in Marine Science, 7. https://doi.org/10.3389/fmars.2020.00434
Wensink, S. M., & Tiegs, S. D. (2016). Shoreline hardening alters freshwater shoreline ecosystems. Freshwater Science, 35(3), 764–777. https://doi.org/10.1086/687279