Gabions

Coastal Protection: Gabions

What are they? - Wire cages usually filled with crushed rocks, and then piled up along the shore to prevent or reduce coastal erosion by weakening wave energy.

Stability? - Short term protection of 5 to 10 years.

Durability- Wires need constant maintenance as they are easily corroded by seawater. They are also affected by excessive trampling and vandalism.

Problems - They are unsightly and can become a danger along the beach.

Seawalls

Coastal Protection: Seawalls

Seawalls absorb the energy of waves before they can erode away loose materials.
Seawalls can be made of concrete, rocks or wood.
They are effective in protecting cliffs from erosion.
They can only absorb the energy of the oncoming waves. They do not prevent the powerful backwash of refracted waves from washing away the beach materials beneath the walls.
Base of seawalls will be undermined and leads to their collapse.
Seawals are costly to build and maintain as constant repairs have to be made to prevent their collapse.

Breakwaters

Coastal Protection:

BREAKWATERS

Location:

East Coast Park, Siloso Beach

http://www.geographicasia.com/coasts/ecp1.html:

Two new breakwaters have been built at Siloso beach, on the southwest shore of Sentosa island. They will serve to protect the beach there, as erosion has been accelerated by the wash from the high-speed ferries plying between the nearby World Trade Centre and the Riau islands of Indonesia. At almost a kilometre in length, Siloso beach is the longest of three artificial beaches built at a cost of $20 million in 1991. The new breakwaters cost more than $1 million. They are each eighty metres long and are placed about a hundred metres offshore.

Breakwaters are only needed at Siloso Beach and along the East Coast Park because elsewhere in

Singapore, longshore drift is negligible.

How:

The breakwaters may be small structures, made of granites and placed one to three hundred feet offshore in relatively shallow water, designed to protect a gently sloping beach

When oncoming waves hit these breakwaters, their erosive power is concentrated on these

structures some distance away from the coast. In this way, there is an area of slack water behind

the breakwaters, which thus will reduce erosion.

Limitations:

When the breakwaters deflect the incoming waves before they reach the shore, these

waves that are deflected to other places (exposed areas of the coast) causing erosion.

Breakwaters are unable to provide complete protection for the whole coast and therefore

unprotected areas will prone to erosion.

Coastal Protections

HARD ENGINEERING

1. Groynes

2.Seawalls

3. Breakwaters

4. Gabions

SOFT ENGINEERING

1. Beach Nourishment

2. Planting mangroves along the shore

3. Growing of coral reefs

4. Stabilising coastal dunes

Groynes

Coastal Protection: Groynes

A groyne creates and maintains a wide area of beach or sediment on its updrift side, and reduces erosion on the other.
-It is a physical barrier to stop sediment transport in the

direction of long shore transport.
-This causes a build-up, which is often accompanied by

accelerated erosion of the down drift beach, which receives little or no sand from long shore

drift.
-Groynes do not add additional material to a beach, but merely retain some of the

existing sediment on the up drift side of the groynes.
-If a groyne is correctly designed, then

the amount of material it can hold will be limited, and excess sediment will be free to move

on through the system.
However, if a groyne is too large it may trap too much sediment,

which can cause severe beach erosion on the down-drift side.

-Intensity and character of groynes influence on shore behaviour depend on sea

water level, parameters of waves, currents and sediment supply in the surf zone, as

well as a shape and inclination of the cross-shore profile.

-Protection of the shore by use of one groyne only is most often inefficient. Therefore,

shore protection by groynes is designed as a group comprising from a few to tens of

individual structures.
- Besides its positive influence on the shore, it causes numerous

side effects, mainly in the form of coastal erosion on the lee side of the structure. In

the case of a group of groynes, the above effect appears on the lee side of the whole

system. The
- Loss of contact between a groyne and the shore in an unfavourable

effect. In such a case, long shore flows are generated between the shoreline and the

groyne root. These flows are the reason for washing out of the beach.