Sand Dunes combating Coastal Erosion EarthCache
Sand Dunes combating Coastal Erosion
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Paradise Point on the Gold Coast is a lovely spot to swim,ride your bike,picnic or walk along the boardwalk .
Away from the swimming area are the sand dunes which are helping to protect our coastline from erosion
FACTORS AFFECTING THE RATE OF EROSION
The biggest factor affecting coastal erosion is the strength of the waves breaking along the coastline. A wave’s strength is controlled by its fetch and the wind speed. Longer fetches & stronger winds create bigger, more powerful waves that have more erosive power. As waves approach a coastline they lose energy though because friction with the seabed increases. This means that the bathymetry (the underwater elevation) of the ocean or sea bed also impacts the strength of waves.
Certain landforms further reduce wave’s erosive power. Beaches increase the distance a wave travels before it reaches the coastline’s cliffs and so reduces its energy. Headlands refract waves around them, reducing their erosive power at one location while increasing it at another.
Weathering also plays a role in the rate of erosion by creating weaknesses in rocks that are exploited by the processes of erosion. Freeze-thaw weathering, for example, creates cracks in rocks, increasing the rock’s susceptibility to hydraulic action.
As always, humans have an impact on coastal erosion. Human activities have a variety of complex effects on coastal erosion but most commonly the activities increase the strength of waves. One activity, dredging, is commonly carried out to improve shipping capacities but it reduces the amount of energy dissipated from incoming waves and so increases erosion
LITHOLOGY
Lithology refers to the physical properties of a rock such as its resistance to erosion. The lithology of a coastline affects how quickly it’s eroded. Hard rocks (e.g., Gabbro) are resistant to weathering & erosion so a coastline made of granite will erode slowly. Soft rocks (e.g., Limestone) are more susceptible to weathering & erosion so a coastline made of chalk will change relatively quickly.
COASTAL DUNES
Dunes—nature's coastal defence
Most beaches are backed by vegetated sand ridges called dunes, built up by dry beach sand blown inland and trapped by plants and other obstructions. As sand accumulates, the dunes become higher and wider.
Plants play a vital role in this process, acting as a windbreak and trapping the deposited sand particles. A characteristic of these plants is their ability to grow up through the sand and continually produce new stems and roots as more sand is trapped and the dune grows.
In our haste to get to the water we often over look the amazing vegetation that assists in the forming and shaping of the dunes .
The dune vegetation captures and traps wind blown sand.Holding sand'bank'for future erosion events.
Their masses of intertwining roots stabilize the sand and most importantly assist in beach recovery after an erosion event .
Without these plants much of the sand would be blown away .
Coastal dunes
Stable sand dunes play an important part in protecting the coastline. They act as a buffer against wave damage during storms, protecting the land behind from salt water intrusion. This sand barrier allows the development of more complex plant communities in areas protected from salt water inundation, sea spray and strong winds.
The dunes also act as a reservoir of sand to replenish and maintain the beach at times of erosion.
The sensitive side of the beach
Frontal sand dunes are vulnerable. The vegetation can be destroyed by natural causes such as storms, cyclones, droughts or fire, or by human interference such as clearing, grazing, vehicles or excessive foot traffic. If the vegetation cover is damaged strong winds may cause 'blowouts' or gaps in the dune ridge. Unless repaired, these increase in size; the whole dune system sometimes migrates inland covering everything in its path. Meanwhile, with a diminished reservoir of sand, erosion of the beach may lead to coastal recession.
To avoid this, protecting the vegetation is vital.
The beach between high and low tides is resilient but the sensitive dunes that we cross to reach it must be protected also. For this reason damaged and sensitive dunes might need to be fenced and access tracks for vehicles and people provided.
For the sake of our coast we must care for the dunes.
Plants on the beach
Vegetation on the beach and dunes tends to occur in zones, according to the degree of exposure to harsh coastal conditions.
Closest to the sea is the pioneer zone, extending landward from the debris line at the top of the beach in an area called the foredune or frontal dune.
Only specialised pioneer plants can colonise areas exposed to salt spray, sand blast, strong winds and flooding by the sea. They are often protected by waxy or hairy coverings on stems and leaves and grow low to the ground, offering little resistance to the wind. They have strong root systems and spread rapidly. They create a mesh of creeping stems so if one part is buried in shifting sand or uprooted another part can continue growing; and so they serve to stabilise the sand, forming and building dunes.
Beach spinifex grass (Spinifex sericeus) and goat's foot convolvulus (Ipomoea pes-caprae) are two of the most common of these herbland plants in the pioneer zone.
Close behind these plants on the frontal sand dunes, coastal she-oaks (Casuarina equisetifolia) are commonly found. The composition of this zone can reveal the condition of the beach. Extensive areas of herbland plants suggest that sand is accumulating; but where they are absent, especially if she-oaks are perched close to the high tide zone, erosion is likely to be occurring. Other trees of this zone are Pandanus species, coastal banksia (Banksia integrifolia) wattles (Acacia spp.), beach almond (Terminalia spp.) and beach calophyllum (Calophyllum inophyllum). The actual species found will depend on the climate. Fruits and seeds from all these species are often found in the flotsam.
Behind the frontal dunes, in areas protected from windy and salty conditions, vegetation depends on local circumstances. Freshwater swamps are usually dominated by paperbark teatrees (Melaleuca spp.) whereas, on higher better-drained ridges, woodlands of Eucalyptus and Acacia species or low rainforest (beach scrub) develop.
These zones are not fixed. As plants grow taller and humus such as dropped leaves accumulates, exposure to sun and soil conditions change. The soil becomes richer and holds more water. This enables scrub and woodland plants to move in, changing the type of vegetation type by a process called succession.
Man must help protect our coastline from further erosion .
Information gathered for this cache was obtained from the web
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A sign at ground zero placed by the council
To log this cache you must first send answers to questions listed below then all good to log
I will get in touch if need be .
Q1
Why are stable sand dunes important .
Q2
What type of erosion could occur along the coast here .
Q3
At the sign what does it say the foreshore has been shaped by .
Q4
Man has used several barriers here to protect the sand dunes what are they and why
We hope you enjoy your visit to the area
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