Large Amount Of Sediment On The Beach example essay topic

Sediment is material that transported to and from coasts by winds and water. Sediment flows in and out of coastal systems. The amount that enters a system is referred to as the sediment input and the amount that leaves is known as the sediment output. By deducting the sediment output from the sediment input we are able to determine the sediment budget. Coastal sediment budgets are largely determined by the rates of erosion and deposition on the coast by various processes such as waves, tides, currents and winds. High energy waves pound coastlines and place headlands and cliff faces under intense hydraulic pressure having the effect of weakening rock and sediment particles causing them to become dislodged and mobilised.

The waves breakout from the shore and because of their high energy the waves' backwash remains strong enough to remove sediment particles as it retreats back into the sea. As high energy waves serve to carry away sediment particles the result is an increase in the sediment output of a coastal system. It is for this reason that high energy waves play an extremely important role in the coastal sediment budget. Compared to the rest of New South Wales the Northern beaches of Sydney experience the greatest number of storms, which also tend to occur in groups. The debate about storm damage is an extremely important one as millions of dollars of local property in prime foreshore locations are susceptible to the effects. By building on active beach zones residents have subjected their properties to then constant change of coastlines and wave action can undermine these buildings and in some case destroy them.

Development has also had a major impact on the dune systems surrounding the area's beaches. The dunes have been levelled to make way for property development. The result has been that sand previously available for beach replenishment is now reduced. When powerful storms occur and a large amount of sediment is removed from the beach the sand previously present in the dune system is not available to replace the sand lost. When there is a large amount of sediment on the beach than the power of waves is reduced and they become less erosive as the sediment help to absorb energy. However the next time storms occur there is less protection for the property occupying land that was previously the dune system thus greater destruction occurs.

Local residents have an obvious obligation to protect their investments and as a result sea walls consisting of large boulders and rocks have been built right on the beach. The purpose of these sea walls is to protect the properties that lie directly behind them, built on what was previously the fore dune, from the effects of storms. The sea walls are also a crude attempt by the local authorities to reduce increasing beach erosion caused by the loss of sand dunes. However the only result has been that increased scouring now occurs caused by the force of waves rebounding back off the rocks and boulders carrying away more sediment than before.

This has destroyed the profile of parts of Narrabeen Beach leaving almost no sand behind in certain areas of the beach. The sediment being carried away from areas of the beach where development has taken place may be responsible for another of the areas' problems. High energy tides and currents as well as the process of long shore drift are causing the sediment to be carried to the northern end of the beach where the entrance to the sea, of Narrabeen Lake, has been blocked by sediment deposits. This causes additional problems for the environment surrounding the lagoon.

A blocked entrance greatly increase the risk of the flooding when the lagoon's catchment area receives heavy rain and will also reduces the water quality of the lagoon as very little exchange of water between the lagoon and the sea will be taking place. An understanding of the coastal sediment budget and interaction of key biophysical processes as well as existing evidence tells us that previous management strategies for the Narrabeen coastal environment have been inadequate. It also tells that although measures have been taken in the past to reduce storm damage, these are not sustainable in the long term. The mistakes of the past, including development on active beach zones, the dumping of ineffective sea walls, and the destruction of sand dune systems, have led to many problem which are difficult and extremely expensive to manage today. It is for these reasons that effective management strategies need to be developed. The Warring ah Council has considered a number of strategies and their costs.

A sea wall survey in 1999 costing $50 000 found that the current boulder sea walls are inadequate for a major storm. This evaluation is an accurate assessment and a positive step for the improving the condition of the beach. The strategy of the reconstruction and linking of existing seawalls is one that costs in excess of $11 million dollars. Having already explained the detrimental effects of the existing sea walls it would be entirely inappropriate and undesirable for this strategy to be implemented, as it would only lead to more significant beach erosion. The strategy would not be financially viable either as the seawalls would also need to be maintained and reconstructed in the future requiring even more money. The strategy of sand nourishment is a process involving sand being dredged from the sea floor or river estuaries and then being dumped on beaches.

This strategy is theoretically possible and occurs in other parts of Australia such as Cronulla Beach however there is no available source of sand to mine for the replenishment of Colla roy and Narrabeen Beach. Also as the dredged sands tend to be finer and more easily eroded than beach sands they replace they provide only short term protection from storm damage. Although this strategy is preferable to the reconstruction of sea walls it would cost between $5-$15 million dollars and would need to be repeated if the problems involving increased beach erosion have not been solved. Buy back is a strategy involving the purchase of high risk cottage homes built on active beach zones and returning the land to the sand dune environment that existed prior to development.

This is the most beneficial strategy as it attempts to correct the mistake of building on active beach zones. However its effectiveness is restricted by the willingness of owners to place their properties on the market. We can see from our understanding of the coastal sediment budget that none of the mentioned strategies will be effective on their own. Education programs and other non-structural approaches to coastal management may be needed to change people's attitudes to the use of coastal resources. A combination of land buy back and sand nourishment may be able to improve the condition of the beach in the long term.

For this to be successful the necessity for sea walls has to be removed, meaning that there will be few properties at risk of storm damage, so that any sand replenished isn't just eroded away in a few years. As well as this the land obtained from buy back should be re vegetated with dune vegetation. These developing dunes should be protected from disturbance by being fenced off with paths through the areas offering people access to the beach. This allows sand to accumulate there over time and eventually the sand dunes are returned to the area.

Bibliography

A Geography Of Global Interactions 1: Preliminary Course Grant Klee man Roger Epps David Hamper Christopher Lloyd Barbara Rugendyke Meg Serval Pages 101 to 135 James Ruse Ag. High Year 11 Geography Field trip Coastal Environment Centre (worksheet) (information copied from Andrew Teh) Info sheets Storm Damage (1974) Wave Climate.