Saturday, 14 December 2013

Reference


these are our reference...

coastal-erosion09.pdf

Controlling-Coast-Erosion-Informational-Slides.pdf

Erosion strategy edoc.pdf

GuidetoErosionProcess.pdf

LabHandout.pdf

Case study : Kwazulu-Natal, south Africa

there are an article title " Living With Coastal Erosion In Kwazulu-Natal". The writer wrote about coastal erosion that happened to surround Kwazulu-Natal, South Africa...
Continued global warming will cause sea-level rose and increased intensity and frequency of coastal storms.
Below, is the picture to prove that coastal erosion that can harm living things on the continental crust.
 ( January 2007)
(July 2007)

The rate of coastal erosion is very fast. In just a few month the beach are almost gone. 
Coastal erosion results in three different types of impact :
- loss of land and damage to the built environment
- destructing  of natural sea defenses such as dunes
- undermining and failure of artificial sea defenses



Mitigation of Coastal Erosion
Mitigation schemes use a combination of techniques and approaches which may include
- Hard engineering techniques : using permanent concrete and rock constructions to fix or consolidate the coastline and protect the inland assets.
- Soft engineering techniques : building with natural process in mind relying on natural elements such as sand dunes,vegetation to prevent erosive forces from reaching the built environment, and the use of sandbags and beach nourishment schemes.
- Managed retreat - removal and relocation of houses and other infrastructure away from erosion prone areas.

But, each techniques have their positive and negative effects.


A short-term responses strategy
- Plan any coastal construction so that it is a safe distance away from the high-water mark and reinstate natural defence mechanism with necessary
- Replace lost sand with sand
- Soft engineering solutions
- Consider hard engineering solutions in exceptional cases only after detailed environmental assessment and authorization is obtained.



p/s : click on image to enlarge it


Controling Coastal Erosion


There are two ways to control coastal erosion or prevent coastal erosion from it get worst. 

(click image to enlarge)

Hard structural are as follow :






Soft structural : Beach nourishment
- is the addition of sand and sediment to the beach to replace the sand and sediment that has been eroded away.
- the replacement sand added is oftent different from the natural beach sand, maybe bigger or smaller in diameter thus affect the way waves interact with the beach and cause change the shape of beach
- the nourishment sand usually erodes faster than the natural sand on the beach.

Both image showed before (left) and after beach nourishment (right)


Process of transport sand and material to the beach.

Friday, 13 December 2013

Wave action

WAVE
- the main driving force of coastal erosion
- can move material onto, off along the shore depend on the height,
length and direction of the waves
-height and length depend on the  blows over the water
-Waves that generated by storms, wind or fas moving motor craft can cause coastal erosion
-There are two types of wave
   : Constructive wave
   : Destructive wave






(click on the image to enlarge)

Destructive wave
-High energy waves that erodes the coast
-They are common along the steep sloping coast
-These waves also called plunging breakers where it  tend to carry material off the beach and into the sea.
-Produced by waves of short wavelength  and high    height





Constructive wave
-Low energy and are common along gently sloping coasts
-The swash stronger than backwash
-Also called spilling breakers which produced by waves af long wavelength and low height




Wave action
Corrasion/abrasion is when waves pick up beach material (e.g. pebbles) and gradually erode the coast.
Hydraulic action occur when waves striking a cliff face compress air in cracks on the cliff face this trigger pressure on the surrounding rock, rock crack and remove piece by piece.
Attrition occur when waves cause loose pieces of rock debris (scree) to collide with each other, grinding and chipping result in small size. Scree also collides with the base of the cliff face and have a corrasion effect
Corrosion occur when waves break on cliff faes and slowly erode it



The Impact

Coastal erosion will change the landform of the coastal. Some coastal landforms serve as natural erosion protective features, minimizing the amount of coastal erosion to land and structure behind them. These includes beaches and dunes, bluffs, stacks, stumps, caves, offshore bars, spits and shoals, bays and headlands, and coastal wetlands and the vegetation on them.


Bays and headlands
Headlands form along coastlines in which bands of soft and hard rock outcrop at right
angles to the coastline (see image below). Due to the different nature of the rock erosion
occurs at different rates. Less resistant rock (e.g. boulder clay) erodes more rapidly than
less resistant rock (e.g. chalk).



Stack, stump and caves
-These features are formed on cliffs or headlands. Waves attack vertical lines of weakness in the rock known as faults. Processes such as hydraulic action and abrasion widen these faults into cracks and eventually the waves will penetrate deeply enough to create caves.

-Over time, the cave will be eroded into an arch, accessible to the sea on both sides.  Weathering will also play a role, with physical weathering processes such as freeze thaw and salt crystallisation and chemical processes such as carbonation weakening the rock surrounding the cave or arch making it more susceptible to mass movement and collapse.

-Finally, the erosion and weathering continues and the arch collapses leaving behind a stack (a vertical column of rock) .  These stacks can be attacked further, and eventually the stack may collapse to leave a low lying stump. 



Thursday, 12 December 2013

Factors that influence..

The factors can be divided in three : primary, secondary and tertiary factors. 

Primary factors
•The hardness or ‘erodibility’ of sea-facing rocks is controlled by the rock strength and the
presence of fissures, fractures, and beds of non-cohesive materials such as silt and fine sand.
•The rate at which cliff fall debris is removed from the foreshore depends on the power of the
waves crossing the beach. This energy must reach a critical level to remove material from
the debris lobe. Debris lobes can be very persistent and can take many years to completely
disappear.

•Beaches dissipate wave energy on the foreshore and provide a measure of protection to the
adjoining land.
The stability of the foreshore, or its resistance to lowering. Once stable, the foreshore should
widen and become more effective at dissipating the wave energy, so that fewer and less
powerful waves reach beyond it. The provision of updrift material coming onto the foreshore
beneath the cliff helps ensure a stable beach.
The configuration of the seafloor, controls the wave energy arriving at the coast, and can
have an important influence on the rate of cliff erosion. Shoals and bars offer protection from
wave erosion by causing storm waves to break and dissipate their energy before reaching
the shore. Given the dynamic nature of the seafloor, changes in the location of shoals and
bars may cause the locus of beach or cliff erosion to change position along the shore.
•Coastal erosion has been greatly affected by the rising sea levels globally.  

Secondary factors
Weathering and transport slope processes
Slope hydrology
Vegetation
Cliff foot erosion
Cliff foot sediment accumulation
Resistance of cliff foot sediment to attrition and transport
Human Activity

 Tertiary factors
Resource extraction
Coastal management

The Definition

Coastal erosion is defined as 
‘the process of episodic removal of material at the shoreline leading to a loss of land as the shoreline retreats landward’.
The processes involved incoastal erosion include not only the work of the sea, but also that of the wind, migrating river mouths and tidal inlets, coastal landslides and tectonics which may take the form of long-term losses of sediment and rocks, or merely the temporary redistribution of coastal sediments; erosion in one location may result in accretion nearby.

Images of coastal erosion