What are groynes? |
Groynes are one the most commonly seen sea defences around the world. The reasons why can be because it is cheaper and yet effective comparing to other sea defences that might be much more expensive. The advantage of groynes are it will prevent long shore drift, which means less sands will be washed away. This will also help to absorb energy created from waves which will decrease the chance of cliff erosion. The groynes are usually made out of wood, concrete, or rock plies, and placed in bulk. It is a barrier constructed at a right angle towards the beach to retain material. Any materials that is trapped between the groynes stays there. |
Example - Kirra Beach/ Gold coast
An example of beach that I've chosen to demonstrate groynes is the Kirra Beach side. It is located in Gold Coast, Queensland, Australia. The Government of Queensland started building the groynes in 1972 and it's purpose was to trap sands preventing further erosion to the beach. The groynes in Kirra Beach, also known as the "big groynes" starts from the North and outstretch up to the Coolangatta beach on the south.
In the beginning, there were people especially surfers who strongly disagree about the plan of building groynes as they believe it would affect the break of waves. There were a few protests and also held by the local organizations back in the 1970s. What they didn't hope to happen turned into a reality, the breaks of the waves weren't as good as the past after the groynes were launched. This has also caused a decline in the tourist rate as well as the local visitors. But miracle happened after the first year, the sand returned and the result of it is that the waves ate breaking than before.
In 1975, another smaller groyne was built and is refered to "little groyne" now. It is located on the north of Kirra Beach to prevent the area from erosion. As a result, the groynes have prevented the waves from carrying the sands away and eventually eroding the area. By 2003, the two groynes are completely covered by sands and in 2006 the Griffith University Coastal management Center has lauched a project to restore the beach.
In the beginning, there were people especially surfers who strongly disagree about the plan of building groynes as they believe it would affect the break of waves. There were a few protests and also held by the local organizations back in the 1970s. What they didn't hope to happen turned into a reality, the breaks of the waves weren't as good as the past after the groynes were launched. This has also caused a decline in the tourist rate as well as the local visitors. But miracle happened after the first year, the sand returned and the result of it is that the waves ate breaking than before.
In 1975, another smaller groyne was built and is refered to "little groyne" now. It is located on the north of Kirra Beach to prevent the area from erosion. As a result, the groynes have prevented the waves from carrying the sands away and eventually eroding the area. By 2003, the two groynes are completely covered by sands and in 2006 the Griffith University Coastal management Center has lauched a project to restore the beach.
Advantage of groynes
- It traps sediments from long-shore drift
- Coastal erosion on beach will be reduced
- Low maintenance
- Able to build it at a low cost
Disadvantage of groynes
- They prevent beaches down the coast from having sediments deposited there which can lead to soil erosion
- Does not protect coasts from storm driven waves approaching the shore
- Causes coast to be unnatural
- Protection of one groyne only is often inefficient and therefore many groynes are designe comprimising froma few to tens of individual structures which can cause people to be unattracted
- If erosion breaches the seawall, then debris from the wall will be left on the beach and in the surf.
What is Beach Nourishment?
Beach nourishment is the process of moving sands from offshore or inland sources and depositing it into the beach by truck, barge, boat or pipeline. This method combats erosion by replacing eroded materials and supplying new sands to long shore through natural process and eventually increase the growth of beach's down drift. To achieve the best result of beach nourishment, the size and quantities of sand must be researched and experiment if it matches the wave conditions. Besides, a balance must be reached between the sand that are originally at the beach and the new sand that are transferred from else where. The purpose of this is to allow enough sand at the beach to be carried along shore and also maintains active beaches down-drift. However, the disadvantage of beach nourishment is it must be repeated regularly and is expensive.
Example - North Cronulla Beach
This is the 2nd example of successful coastal management in Australia that i have chosen to explain. Since 1970's, the idea of beach nourishment was introduced to Sydney. However, only a minimal nourishment has taken place at Cronulla and Manly beach. As they only place around 10000s m3 of sand, so the result didn't really make a difference to the beach. As time goes by, the beaches has been eroded further to the civilization areas like the photo above. Because there weren't any actions taken place, it eventually resulted in loss of visitor and surfers.
North Cronulla Beach is located on the east coast of Australia, 29km from the centre of Sydney. It was a beautiful beach until the waves started to become weak and it was eroding further to the building. Therefore, some parts of the beach were severely affected by the wind aspect from the South which gradually had caused the waves height to shrink from at least 10 meters to only 2 meters. In 2000, the local government has finally agreed to use Beach Nourishment to improve the wave breaking for the Cronulla Beach. At the end of the year, they have started plugging the sands on to ground collected from the Stockman and Palm Beach which is less popular. It was estimated that 10 million m3 of sands will be pump on the Cronulla Beaach by 2020.
After the nourishing in Cronulla beach, the strong waves breaks have came back or even better than in the past. NOw, there's a stabilized population of visitors and surfers who always come to the beach for recreational purpose. Besides, the residence who lives near the sea wouldn't have to worry about the erosion in the next few years.
In conclusion, beach nourishment can definitely serve the beach good as it will become wide and good for surfing, especially if it produced better banks. The wider beach is also good for protection of any exposed property or facilities behind the beach, such as surf clubs, car parks, houses etc. All this means visitors will have a wider and more useful beach, as well as a softer sands.
North Cronulla Beach is located on the east coast of Australia, 29km from the centre of Sydney. It was a beautiful beach until the waves started to become weak and it was eroding further to the building. Therefore, some parts of the beach were severely affected by the wind aspect from the South which gradually had caused the waves height to shrink from at least 10 meters to only 2 meters. In 2000, the local government has finally agreed to use Beach Nourishment to improve the wave breaking for the Cronulla Beach. At the end of the year, they have started plugging the sands on to ground collected from the Stockman and Palm Beach which is less popular. It was estimated that 10 million m3 of sands will be pump on the Cronulla Beaach by 2020.
After the nourishing in Cronulla beach, the strong waves breaks have came back or even better than in the past. NOw, there's a stabilized population of visitors and surfers who always come to the beach for recreational purpose. Besides, the residence who lives near the sea wouldn't have to worry about the erosion in the next few years.
In conclusion, beach nourishment can definitely serve the beach good as it will become wide and good for surfing, especially if it produced better banks. The wider beach is also good for protection of any exposed property or facilities behind the beach, such as surf clubs, car parks, houses etc. All this means visitors will have a wider and more useful beach, as well as a softer sands.
Advantages
- Nourishment restores and widens the recreational beach.
- Structures behind beach are protected as long as the added sand remains.
- When erosion continues, beach nourishment does not leave hazards on the beach or in the surf zone. This is a big advantage when compared with "hard" beach stabilization structures like seawalls or groins.
Disadvantages
- Beach nourishment sand usually erodes faster than the natural sand on the beach. Therefore regular preservation is required.
- As storms are unpredictable, therefore the nourished beach lifetimes is not guaranteed as storm is one of the factors that might are unpredictable too.
- Beach nourishment is expensive, and must be repeated periodically. Except on very small beaches, the minimum expenditure is usually $1 - $2 million dollars; larger, longer-lasting projects often cost much more (e.g., $100 million - 1 billion).
- The beach turns into a construction zone during nourishment.
- The process of nourishment may damage, destroy or hurting marine and beach life by burying it, squishing it under bulldozers or changing the shape of the beach.