Coastal Erosion - It all comes out in the backwash

Caitlin Carpenter

Global Studies student, Monash University

‍

Through a combination of sea level rise and higher energy storms, climate change is beginning to eat away at our beaches.

That not only degrades the environment and destroys infrastructure, it also erodes our very culture. So what can we do about it?

‍

Like most Victorians, I have a deep-seated connection to the beach. It's a place to build sandcastles, surf/swim in some ‘killer’ waves, and socialise with loved ones. To me, the beach epitomises a relaxing and peaceful life.

So you can imagine my concern when I began to learn about coastal erosion. This process, which climate change exacerbates, puts a thing of natural beauty at risk. In fact, about 50% of Australia’s coastline will be “severely threatened by 2100”¹. But the effects of coastal erosion are already visible today.

‍

Coastal erosion is a natural process that involves the “net removal of sediment”². Essentially, the shoreline recedes when the beach loses more sand than it receives. It is important to note that coastal erosion can have a varying timeline². It can be short-term, i.e. days to weeks, or long term, years to decades.

‍

It’s all to do with waves. The interaction of a wave with the shore comes in two phases. The movement of water onto the beach, which most of us consider a ‘typical wave’, is known as the swash³. But there also is the pull of the wave back to the ocean, which is called the backwash³. Depending on the relative strength of these two parts, there are two sorts of waves. Constructive waves have a stronger swash, so more sediment is dumped onto the beach; destructive waves have a stronger backwash that “pulls material away from the shoreline”³.

‍

The movement of sediments, known as longshore drift, is also a significant factor in coastal erosion⁴. This occurs when, directed by a strong ‘prevailing’ wind, the swash approaches the beach at an angle, but the backwash recedes perpendicular to the coast, so the sand is pushed along the coastline⁵. If the sand is constantly moving in one direction, the beach very quickly becomes uneven. This leaves some parts of the beach and the rock inland more exposed to eroding, destructive waves.

‍

‍

Why is coastal erosion so bad?

Each different ‘zone’ of a beach provides a different habitat for a wide variety of animals⁶.

Biologically, erosion causes a “landward migration of habitats”⁷, putting a strain on existing ecosystems. Many native species are put at severe risk⁸. Studies, such as Clemens, et al. (2016), for example, have shown a significant population decrease in 17 out of 19 southern Australian migratory shorebirds⁹. Population shifts can create flow-on impacts throughout food webs, leading to further instability and threatening coastal biodiversity.

Economically, the impacts of erosion include property damage, loss of tourism, loss of land, and the costs of rebuilding infrastructure (such as roads and footpaths)¹⁰. Each year Australians make about 31 million day trips to the beach¹¹. Beach tourism is an important part of Australia's economy.

Another social impact is simply the loss of beaches themselves. They provide aesthetic  and recreational opportunities, and for some, a sense of place¹². For Victorians, the beach can be an escape from regular work life. These unquantifiable impacts are equally important to consider when studying coastal erosion.

‍

What’s climate change got to do with it? 

While coastal erosion is a normal process, climate change, population growth and human activity all exacerbate its impacts¹³, leading to more severe erosion and less time to implement management strategies. Climate change also increases the frequency and severity of storms¹⁴ which, in turn, increase short-term coastal erosion.

Sea level rise is another factor that amplifies the impacts of coastal erosion⁷. First, it shifts the intertidal zone, which means waves reach further up the beach and erode areas that have been previously left untouched⁷. Second, if reefs and rocks are submerged more deeply in the water, they can no longer disrupt the wave’s energy, a process that tends to reduce the intensity of the destructive waves ⁷.

‍

So how do we stop this?

Mitigation comes in many forms. There are hard engineering measures, which is the physical construction of structures to block erosion¹⁵. An obvious example is building a seawall that blocks waves from hitting more vulnerable land behind.

There is also soft engineering management, such as native vegetation, which can protect dunes and, therefore, the beach¹⁶. Soft engineering involves “a more sustainable and natural approach”¹⁵ than physical man-made structures, but generally takes a lot more time.

Groynes are the perfect example of hard engineering¹⁷. These structures are built perpendicular to the shoreline. Normally there are several over a stretch of beach. They are designed to reduce longshore drift, acting as a physical blockade to prevent the extreme movement of sand¹⁸. Rock groynes generally have a simple construction, demand relatively low maintenance, are durable – lasting 30 to 50 years – and are reasonably permeable. Thus, they are effective at absorbing wave energy¹⁸. They are not aesthetically attractive, however¹⁹. And they can prevent natural drift of sediments. This might become detrimental to surrounding beaches¹⁸. For a groyne to be most effective, other management strategies, such as beach renourishment, must be used in conjunction with it.

Beach renourishment is a process that involves adding sand to a coastal region that suffers high levels of erosion²⁰. This is considered  an example of “soft” management¹⁵. Due to natural processes, like longshore drift, this management strategy does not have a long lifetime¹⁵. It is useful for delaying the impacts of erosion, however, providing time to find other solutions. It is better to have the waves hit and move the sand than hit and erode the important foundations of rock.

Where the sand for the renourishment comes from is of potential concern²⁰. It can be taken from a wider part of the beach or, by pumping up sediments, from the middle of a bay, lake or ocean. Such dredging can be detrimental to marine life²¹.

An example of beach renourishment in action is the Dendy Street Beach in Brighton,  home to a famous set of bathing boxes, and a critical social, economic, and cultural hotspot. The local council has moved about 3500 cubic metres of sand for its immediate protection. This solution, however, it is going to only last 3 to 5 years²².

Like most natural processes, coastal erosion will be amplified by climate change to levels where humans cannot cope. The least all of us can do is learn more about coastal erosion, stay on the pre-formed paths (which reduces human erosion), and alert the local council if there are any local erosion concerns.

Future generations should be able to enjoy beaches just as much, and in the same state, as we do now.

‍

References

1. ://www.gsi.ie/en-ie/geoscience-topics/natural-hazards/Pages/Coastal-erosion.aspx 
2. Geoscience Australia. (2023. Coastal erosion. www.ga.gov.au. https://www.ga.gov.au/education/natural-hazards/coastal-erosion
3. US Department of Commerce, National Oceanic and Atmospheric Administration. (2019). Longshore currents - Currents: NOAA’s National Ocean Service Education. noaa.gov. https://oceanservice.noaa.gov/education/tutorial_currents/03coastal2.html 
4. LibreTexts Geosciences. (2020). 12.10: Longshore Currents and Longshore Drift. Geosciences LibreTexts. https://geo.libretexts.org/Bookshelves/Oceanography/Oceanography_101_(Miracosta)/12%3A_Coasts/12.10%3A_Longshore_Currents_and_Longshore_Drift 
5. Mazor, T., et al. (2023). Statewide Marine Habitat Map: Habitat Complex Modelling Method (CBiCS Level 3). In www.marineandcoasts.vic.gov.au, Victoria Department of Energy, Environment and Climate Action. https://www.marineandcoasts.vic.gov.au/data/assets/pdf_file/0027/617607/Statewide-Marine-Habitat-Map-2023.pdf
6. Paice, R. & Chambers, J. (2016). Climate change impacts on coastal ecosystems. National Climate Change Adaptation Research Facility. https://coastadapt.com.au/sites/default/files/factsheets/T312_9_Coastal_Ecosystems.pdf 
7. Von Holle, B., et al. (2019). Effects of future sea level rise on coastal habitat. The Journal of Wildlife Management 83 (3): 694–704. doi.org/10.1002/jwmg.21633 
8. Clemens, R., et al. (2016). Continental-scale decreases in shorebird populations in Australia. Emu - Austral Ornithology, 116 (2): 119–135. doi.org/10.1071/mu15056 
9. Reiff, N. (2022). The Economic Impact of Coastal Erosion. Investopedia. https://www.investopedia.com/the-economic-impact-of-coastal-erosion-5220483 
10. Tourism Research Australia. (n.d.). Beaches. In Tourism Research Australia (pp. 1–2). Australian Government, Austrade. From https://www.tra.gov.au/content/dam/austrade-assets/global/wip/tra/documents/tra-domestic-visitor-profiles-beach.pdf 
11. Lakshmi, A. (2021). Coastal ecosystem services & human wellbeing. Indian Journal of Medical Research 153 (3): 382–387. doi.org/10.4103/ijmr.IJMR_695_21 
12. Victorian State Government. (2023). Coastal erosion. In www.marineandcoasts.vic.gov.au, Victoria Department of Energy, Environment and Climate Action. https://www.marineandcoasts.vic.gov.au/marine-coastal-management/coastal-erosion
13. NSW Government . (n.d.). Sea level rise. AdaptNSW, NSW Government . https://www.climatechange.environment.nsw.gov.au/impacts-climate-change/weather-and-oceans/sea-level-rise
14. BBC. (2019). Coastal management - AQA - Revision 1, GCSE Geography - BBC Bitesize. BBC Bitesize. https://www.bbc.co.uk/bitesize/guides/z2234j6/revision/1
15. Bird, E. & Lewis, N. (2014). Responses to Beach Erosion. SpringerBriefs in Earth Sciences, 29–39. https://link.springer.com/chapter/10.1007/978-3-319-09728-2_3  
16. Lee, N. (2004). Erosion on the Yorkshire coast. Geography Review 18 (2):18+ https://link.gale.com/apps/doc/A124791871/ITOF?u=monash&sid=bookmark-ITOF&xid=4926ddb6 
17. RISC-KIT. (n.d.). Groynes | In Coastal Management Webguide  www.coastal-management.eu. https://www.coastal-management.eu/measure/groynes 
18. The Flood Hub. (2021). Coastal Flood Defences: Groynes. https://thefloodhub.co.uk/wp- content/uploads/2019/01/Groynes.pdf 
19. US Army Corps of Engineers, Institute for Water Resources Website. (n.d.). Beach Nourishment. www.iwr.usace.army.mil https://www.iwr.usace.army.mil/Missions/Coasts/Tales-of-the-Coast/Corps-and-the-Coast/Shore-Protection/Beach-Nourishment/ 
20. Todd, V. L. G., et al. (2014). A review of impacts of marine dredging activities on marine mammals. ICES Journal of Marine Science, 72 (2): 328–340. doi.org/10.1093/icesjms/fsu187 
21. Stantec. (n.d.). Dendy Street Beach Renourishment. www.stantec.com. https://www.stantec.com/en/projects/australia-projects/d/dendy-street-beach-renourishment 
22. Crothers, J. (2018). Great Ocean Road erosion prompts call for plan to preserve tourist destination's future. ABC News. https://www.abc.net.au/news/2018-08-26/erosion-threatening-great-ocean-road/10147918
23. Dipper, F. (2022). Elements of Marine Ecology (5th ed.). Butterworth-Heinemann. https://www.sciencedirect.com/book/9780081028261/elements-of-marine-ecology#book-info
24. Mid-Vancouver Island Habitat Enhancement Society. (2019). Nearshore Ecosystem - MVIHES (Mid-Vancouver Island Habitat Enhancement Society). www.mvihes.bc.ca. https://www.mvihes.bc.ca/current-initiatives/36-general-current/121-nearshore
25. Pew Trusts. (2014). Coral Reefs Reduce Wave Energy and Height. Pew.org. www.pewtrusts.org/en/research-and-analysis/data-visualizations/2014/coral-reefs-reduce-wave-energy-and-height
26. NearMap. (n.d.). High Quality Aerial Imagery Maps & Geospatial Data. www.nearmap.com. https://www.nearmap.com/au/en 
27. AW Maritime. (n.d.). Brighton Beach Renourishment, VIC. AW Maritime. https://www.awmaritime.com/projects/brighton-beach-renourishment/ 
28. Main banner image from Jamie Davies via Unsplash