Beach erosion is a natural process and typically happens seasonally throughout the year. There are a wide range of factors that may cause greater than expected erosion and potential property damage. This article looks at beach erosion prevention solutions and how best to integrate them into a site.
What is Beach Erosion and How is it Prevented?
Beach erosion is the loss of sand, rubble and or rock from a beach front over time. There are various degrees of beach erosion that can occur at a site relative to time:
Cyclical erosion – this is typically based on seasonal storm patterns whereby a beach may erode during storm syrge or high wave energy. During the calmer months, the beach will naturally re-build
Significant event erosion – this is where a greater than normal storm event may take place and remove a significant amount of beachfront. During the quitter months some sand may re-build, but it will not be back to the same level it was pre-event
Ongoing erosion – this is where a storm event or season takes place, causing erosion, however, there is no natural sand reserves to replace or rebuild during the quiet months. Therefore, there is a general erosive trend landward that does not stabilise over time.
Is Beach Erosion a Natural Process?
Beach erosion is a natural process. It happens at very different rates depending on the site conditions and can result in one of the above-mentioned erosion types (also site dependant). In many cases where a beachfront is left in its natural state, the erosion that occurs will be cyclical.
This is how natural beaches stay relatively stable over time. With erosion occurring during storm season and deposition (sand build up) during calmer months.
What is the Main Cause of Beach Erosion
Some level of beach erosion occurs on most beachfronts around the world over time. In most cases, beach erosion is only really a problem when it relates property boundaries or infrastructure.
This is when notable changes in the beach require beach erosion prevention solutions.
There are a few factors that contribute to the erosion itself but in many cases, it comes down to a few key factors:
Wave impacts direct on shore have changed
There may be increased wave impacts on a section of coastline. This may be a combination of climate change, increased sea levels or changes to the surrounding areas (human inference)
Reduced sand flow to an area
Generally, occurs with interruption of natural sand flow by man-made structures on nearby site) which can reduce the ability for the beach to naturally build-up back up over time
A beach may be artificially created (or nourished) with a sand that is not well suited for the wave conditions at the site
Beach sand can vary significantly in quality and grain size. Very fine sand requires a significantly flatter slope than larger grains to sit at a ‘stable’ profile
What are the Effects of Coastal Erosion?
Depending on the site and the severity of the erosion there can be different effects.
The most noticeable effects of coastal erosion include:
Beach loss
Property loss
Property damage
Landslides
If erosion is occurring and the beach is not re-building (no deposition during calm months) it is possible that the rate of erosion may increase over time.
The best way to avoid further property loss is to take action as soon as possible.
Ways to Prevent Beach Erosion
There are a lot of beach erosion prevention solutions out there. Each with their own advantages and disadvantages. However, whater the solution may be, there is a process to determine which will work the best for the site.
The general process for preventing beach erosion is to follow the following:
Do a site investigation
This should be done by a professional coastal engineer
It may include survey (both of the land and the sea)
Determine the causes and rate of erosion
This can also be done by a coastal engineer
It can be done using a variety of mathematical equations and even computer simulated models taking into consideration all elements at the site (tide, wind, wave, surrounding interferences that may be man-made or naturally occurring)
Review all relevant coastal erosion solutions with their suitability to site
This takes into consideration things like constructability, cost, aesthetic, efficiency, etc.
Review and narrow down preferred option trough options analysis
Detail a solution
Once a preferred beach erosion prevention solution has been determined, a detailed design can be done.
This will result in drawings and construction material volumes that should be used by a contactor to build
Construct the beach erosion control solution(s)
There may be a variety of different structures and solutions implemented at the site
Monitor the site
It is good practice to follow-up with the site after significant storm events to ensure the design is performing as expected
What is a Way to Stop Coastal Erosion Naturally?
Our environment has developed some amazing nature based solutions to prevent and reduce coastal erosion.
These are referred to as blue/green solutions of which there are two primary types:
Coral reefs
Mangroves
Nourishment
Coral Reefs to Prevent Beach Erosion
Coral reefs are amazing wave breakers and have been said to reduce wave energy by up to 97%.
Coral reefs are also very fragile environments and subject to detrimental conditions (both natural and human influenced), which has led to their demise. In most instances, if the coral reef has degraded to a point where it is no longer acting as a significant wave breaker there is likely a multitude of factors at play which may include overfishing, physical damage from construction, sea temperatures rising, etc.
Therefore, simply planting more coral may work in the short term but if conditions persist, they may be destined for the same fate.
In addition to planting coral, artificial reefs can be used to help reduce wave impact to prevent beach erosion.
Mangroves to Prevent Beach Erosion
Mangroves are one of nature’s most important coastal inventions. Not only do they provide habitat for the majority of juvenile fish species, they act as wave breaking barriers simultaneously reducing wave energy while ‘holding’ the beach in place through a complex root system.
It should be noted that both coral reefs and mangroves do not survive in all weather conditions (the need tropical/sub tropical). However, there are many other types of vegetation that can be used to ‘hold’ beach sand in place.
Why do Plants and Trees Prevent Soil Erosion?
The root systems of coastal vegetation (especially dune vegetation) are dense, which act as a kind of underground ‘net’ to trap sand and soil in position.
Therefore, adding more dune vegetation to a site is a great, natural way to reduce or prevent beach erosion.
‘Soft’ Solutions to Prevent Beach Erosion
Beach nourishment is a widely used form of coastal erosion control, however, it is rarely used as a stand-alone solution.
Typically, beach nourishment (artificially nourishing the beach with imported or local sand) is done in conjunction with a form of ‘hard’ beach erosion control.
This is typically, done so that the newly nourished beach can be ‘held’ in position with some kind of hard structure. However, alternative soft solutions include the creation of offshore sand banks to break waves offshore and reduce the chance of erosion.
Nearshore nourishment can be used to get better cost to volume of sand placement.
Hard Beach Erosion Prevention Solutions
Engineered beach erosion prevention solutions include ‘hard’ structures such as:
Seawalls (make sure you review advantages and disadvantages of seawalls)
Breakwaters
Floating breakwaters
Groynes/ Groines
These can be arranged in a variety of ways to best suit a site. They can also be made from a variety of materials including concrete, rip rap rock, sand filled geotextile containers or modules.
Note that these kinds of solutions should only be installed with consultation of experienced coastal engineers as in many cases, improper installation can actually increase beach erosion and cause further damage to nearby properties.
How do Groynes Reduce Coastal Erosion
One example of how the hard structures (groynes) can reduce beach erosion is that groynes act as beach compartmentalisation structures. This means that they can prevent sand from being lost from the system if there is a significant storm event. In this case the sand may shift slightly within the confines of the groynes, but would not be totally removed from the beach.
The beach may then naturally re-align over time or some maintenance (beach scraping or shitting) can be done to manually shift the beach back into alignment.
Stabilising Shoreland Property to Prevent Erosion
There are a lot of beach erosion prevention solutions available and with the right design, almost any beach can be protected.
In the dynamic, coastal environment things are always changing and therefore need to take into consideration things like sea-level rise, increased storm severity and more.
It is always recommended that a professional coastal engineer be consulted when looking to prevent beach erosion at a site, as in many cases world-wide when coastal structures are installed incorrectly, they can actually cause more damage than good.
Costs Consideration of Beach Erosion Prevention Solutions
There is a range of cost-effective solutions that can be implemented at a site to reduce upfront (capital costs).
It should be taken into consideration that costs for beach erosion prevention solutions can be distributed between capital and maintenance. In general, large upfront costs for large scale construction can lead to minimal need for maintenance or future works, however, if a low impact/low cost solution is preferred then a maintenance plan can also be developed.
For example, a breakwater may be constructed offshore of a site to be large and stop ALL waves at all expected conditions. This would be a significant upfront cost. It would also be a large aesthetic disturbance. However, if reduced in size to be approximately half the size (and cost) and stop waves 60% of the time then, there would be still a significant improvement at the site/reduction in beach erosion compared to the ‘do-nothing’ option. And the cost to maintain the site over time would be much less that the ‘do nothing’ option.
When a coastal engineer reviews relevant coastal erosion prevention solutions (step 3 as mentioned above) costs of capital vs. maintenance should be considered and discussed and built into the design process.