Fig 1: East Coast Park
Introduction
Singapore’s small size coupled with its rapid development has led to massive land reclamation projects to extend its land area and its coastline. East Coast Park is one of the massive tracts of land that has risen from the sea in the recent decades. However, the battle between Man and Nature is not over yet! The sea is still trying to take back the area was once water, and we must fight back.
In this Earthcache, you will learn about the following:
- The natural forces that shape coastlines
- Coastal defence: how we fight back against the sea
- How defences reshape the coastline
Section 1: Getting the into Drift of things
As one might expect, the main forces shaping our coastlines are the waves, which constantly deposit and wash away the sand on the shore as they beat back and forth. The waves mostly deposit as much sand as they wash away, but over time, these small waves can make a huge difference.
In this Earthcache, you will learn about the phenomenon of Long Shore Drift (LSD), where sediments on beaches are transferred in a particular direction along a shore. To understand LSD, we need to divide the process into two parts.
Firstly, when the waves move towards the shore, the sediments they carry are washed up in the direction of the waves. The direction of the waves is dependent on the prevailing wind and current directions in the area, and more often than not, the waves will hit the shore at an angle.
Secondly, as the waves flow back towards the sea, the waves will take the course dictated by gravity back to the sea. Therefore, the waves will recede at right-angles to the shoreline. These waves will wash sediments back into the sea. These two processes repeat themselves over time as the waves move back and forth.
You should notice that these two processes often do not happen in exactly the same direction, so sediments that are washed up the shore will not return to the sea in the same direction. The combination of these two processes leads to the sediments gradually getting transferred along the coastline in the direction of the prevailing wave direction. This is what geologists call the Long Shore Drift (LSD): a drifting of sediments a-long the shore.
Fig 2: Diagram of LSD on a beach. Note how the sediment is washed ashore in the direction of the wind and waves, but is washed back into the sea perpendicular to the shoreline. The combination of the two direction causes the sand to move to the right over time.
Section 2: Coastal Total Defence
LSD can have nasty effects on a beach, as sediment and sand from one area gets pushed up along a shore to the next area. This leads to beach depletion caused by the erosion of the sand. This can be an issue, especially when there are structures near the beach, which will be struck by waves when the beach disappears. So, we have come up with ways to defend the coastline and slow down the effects of LSD. The defence mechanisms can be divided into two broad categories: hard and soft engineering.
Hard Engineering: These methods employ the use of hard structures to either resist or reduce the power of the waves which cause the LSD. The following are a few commonly used strategies.
1. Groynes: These are solid structures build perpendicular to the coastlines. They primarily prevent the drift of sand and sediments further down a beach by acting as a barrier to the sediments’ movement.
Fig 3: Example of a groyne
2. Seawalls: These are long solid structures built along a coastline to prevent further erosion of land by the waves. These structures are very good at their jobs of preventing erosion, but they generally lead to beach depletion in front of the wall. So, it is unsuitable in places where a beach is to be maintained.
Fig 4: Example of a seawall
3. Breakwaters: These are solid structures built near shoreline and usually protrude out to the sea. There are usually built in the water, and serves to reduce the impact of waves when they hit the shore, and thus, reduce LSD. They can be a continuous wall to provide a safe harbour for ships or a series of short parallel walls to protect beaches and provide safe swimming areas.
Fig 5: Example of breakwaters
4. Gabions: These are loose rocks bundled together with a mesh and stacked to form a wall. These are used as alternative to solid walls as they allow some water to pass through them, and can capture sediments in the waves.
Fig 6: Example of gabions
Soft Engineering: These methods involve using less direct strategies to prevent sediments from getting washed away or by replenishing the sediments. These employ techniques like mangrove trees replanting to act as a barrier to strong waves, planting grass and trees to prevent sand from getting washed away and adding more sand to beaches.
Section 3: The Clash of Man and Nature
At the ECP, you will look at examples of how the coastal defences and the force the wave combine to shape the coastline. Making these observations will be the tasks for this EC.
These are the EC tasks:
- Identify the coastal defence structures at WP1 and WP2.
- Estimate the height of the defence structure at WP2 above the high tide mark. This is the height from the high watermark to the top of the structure.
- Describe the profile of the coastline to the east and west of these structures. Guiding questions: What is the shape of the shore (curved or straight)? How wide is the beach? On which side of the structure is the beach wider?
- Based on your observations in Part 2, and the description and diagram showing the mechanism of the LSD above, in which direction do the waves in ECP primarily strike the shore? Towards the North-east, North or North-west? Explain your answer.
Email the answers to the above tasks to me. You may log after sending the e-mail, so, there is no need to wait to wait for a reply. You will hear from me if there are any issues.
Enjoy your trip to the beach!