Sec 2 IDS, 2010Coastal Management

You will learn:

1. Evaluate the feasibility of coastal protection measures at Pulau Ubin

Coastal Management

• Coastal erosion is a landward movement of

the coastline. To prevent erosion,

measures have been take to protect the

coastline. These can include hard

engineering and soft engineering methods.

Hard engineering methods

In marine engineering, hard engineering refers to measure that use man-made and artificial structures such as concrete sea walls to protect the coasts.

• Various types: revetments, rip-rap, concrete walls, piles of rubble, etc.

• Nearly 100% of the time they damage or destroy a beach which is eroding to begin with

From Dean (1999)

Loss of beach

Flooding of beach

Destruction of seawall

Hard engineering methods1. Seawalls

• The essential problem is that the beach is moving landward naturally, but the seawall isn’t

• The result: NO BEACH

Hard engineering methods

• Hugely costly measures are required to restore beach, e.g., pumping sand, and this is only a temporary solution

• Also, houses are now closer to the water and more vulnerable

• On either end of the seawall, the beach erodes and is displaced toward the land naturally…so the walled part of the beach is exposed to the ocean and vulnerable to storms

Hard engineering methods

• Erosion is worst here, with severe scour occurring (this aspect is not well understood)

• This means that seawalls frequently need to be extended, in order to save houses which are vulnerable to being destroyed

From Dean (1999)

Erosion

Hard engineering methods

• Seawalls may even encourage erosion… waves are no longer absorbed by the soft sand

• Instead, the waves bounce off the hard seawall, scouring the beach in front

• The wall eventually fails

Hard engineering methods

Hard engineering methods

http://1.bp.blogspot.com/_vLWmPrr87pw/SkY8F7i1MzI/AAAAAAAAC7k/a4nHZ1P0aXI/s400/breakwater-big.jpg

Breakwaters: can be constructed away from the coast OR with one end linked to the coastErosive powers of waves are concentrated in the breakwaters, while encouraging deposition in the other side

2. Breakwaters

• Designed to allow sediment to settle

• Smaller waves behind, less sediment is transported

From Dean (1999)

Hard engineering methods

• Thus, beach behind breakwater can grow out to it…

• …but the beach down-current is deprived of sand and thus erodes

From Dean (1999)

Experimental breakwater designed to preserve sediment

Hard engineering methods

Hard engineering methods

Hard engineering methods2. Breakwaters

Below is a link which you can find out more on groynes:

http://www.channelcoast.org/programme_design/defence_type/?link=groynes.html

Hard engineering methods3. Groynes

Hard engineering methods3. Groynes

• Designed to trap sediment…

• but they instead progressively starve beach of sediment in the direction of longshore-littoral current

From Dean (1999)http://www.bbc.co.uk/schools/riversandcoasts/coasts/change_coast/pg_18_flash.shtml

Hard engineering methods

This photograph shows how littoral drift was interrupted by the rock groins that stick out into the water. Sand accumulates on one side and erodes on the other. What is the direction of littoral drift here? Shore erosion in this area of coastal New Jersey has caused damage to roads and private property.

Hard engineering methods

Hard engineering methods

Hard engineering methods

• Gabions are wire cages containing rocks which are used to form a seawall, groyne or a breakwater to protect the coast against erosion.

• When a wave breaks on a gabion, the sea water slips through the gaps between the large stones and the waves’ energy is dissipated

Think of one disadvantage in using gabions.

Hard engineering methods

Soft Engineering Methods

• Involves the use of natural processes or

agents to protect or stabilise the coast.– Planting of vegetation– Beach nourishment– Encouraging growth of coral reefs

Soft Engineering Methods1. Planting Vegetation

• Mangrove trees have long roots that traps sediments efficiently, helping to extend the coast into the sea

• They are hardy and able to absorb the impact of waves

• The government is looking at mangrove swamps as a less expensive alternative to building concrete structures to protect the coast

• Examples of sites: Sungel Buloh Wetland Reserve, Pasir Ris Park and offshore islands like Pulau Tekong and Pulau Ubin

Soft Engineering Methods2. Beach Nourishment

• It is the process of adding new beach materials, usually sand to a beach that has been depleted

• The sand is usually similar to the original and is usually dredged from the nearby shallow sea

• The replenished beach serve the main purpose of protecting the coast and the tourism industry

• In some cases, this method is short-lived. Why?

Soft Engineering Methods3. Encouraging growth of corals

• Like mangrove swamps, they are a coastline’s natural defence against waves. The rough surfaces of healthy corals act like natural breakwaters

• Offshore coral reefs have spared many coastal villages in Asia from the 2004 Asia Tsunami

• Due to industrialisation, less than 60% of Singapore’s coral reefs are left.

• The government has set up a coral nursery off Pulau Semakau. When the coral reefs have grown to a certain size, they are sent to the southern coast for propagation, an alternative to protect our coasts.

Coastal Management

1. Name one type of soft engineering method which involves the use of plants.

2. Name two methods which involve the use of sand.

3. Coral reefs are found off shore. What effect do they have on the waves?

Below are terms which you have learnt in this chapter.

Group them into as many meaningful units as possible and provide a heading for every group.

You may use a term more than once. The group with the most groupings wins!

Bay Swash Tide Currents Mangroves

Tombolo Wave refraction

Spit Mangroves Fetch

Groyne Waves Erosion Gabion Wind energy

Cliff Longshore Drift

Headland Deposition Coral reefs

Marram grass

Shore platforms

Backwash Hydraulic action

Beach