Leatherman cites U. In many of these cases, individual beaches may be losing only a few inches per year, but in some cases the problem is much worse. Of particular concern is the effect climate change , which not only causes sea levels to rise but also increases the severity and possibly the frequency of harsh storms, has on beach erosion.
Besides collectively lowering our greenhouse gas emissions substantially, there is little that individuals—let alone coastal landowners—can do to stop beach erosion. Building a bulkhead or seawall along one or a few coastal properties may protect homes from damaging storm waves for a few years, but could end up doing more harm than good. Other larger scale techniques like beach nourishment may have better track records, at least in terms of slowing or delaying beach erosion, but are expensive enough as to warrant massive taxpayer expenditures.
Not only did the effort stave off erosion, it helped revitalize the tony South Beach neighborhood and rescue hotels, restaurants and shops there that cater to the rich and famous. Box , Westport, CT ; submit it at: www.
Read past columns at: www. DEA Coastlines is a free, publicly available dataset that identifies annual shorelines and rates of coastal change along the entire Australian coastline from to the present.
The tool enables historic trends of coastal erosion and progradation growth to be seen at both a local and continental scale. The Smartline national dataset maps record the location of those coastal substrates and landforms that have greater or lesser sensitivity to potential coastal impacts of climate change and sea-level rise IPCC , such as accelerated erosion and shoreline recession, increased slumping or rock fall hazards, changing dune mobility, and other hazards.
Qin, G. Plattner, M. Tignor, S. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P. Midgley eds. Geoscience Australia is committed to support Australia's capability to managing the impact of natural hazards, including coastal erosion. Geoscience Australia:. Sand mining in rivers is a major cause of coastal erosion in many countries. Sand mining in a river lowers the river bed, causes bank erosion and reduces the supply of sand to the coast. There are five components in the sediment balance for a degrading river section, schematically represented in Fig.
Many rivers consist of a steep upper part, the mountain part, and a gently sloping lower part, where the river crosses the coastal plain. Sand extraction in the upper part of the river causes lowering of the river bed and a similar lowering of the water level, hence no changes in the sediment transport capacity. Thus the sand extraction in the upper part of the river is almost entirely balanced by local bed degradation, and has hardly any immediate impact on the supply of sand to the coast.
Sand mining in the lower part of the river at some distance from the river mouth causes a local lowering of the river bed. However, the water level will not lower as much, which results in a local decrease in the flow velocity and in the sediment transport capacity.
The river bed depression will gradually be filled in from upstream supply and will travel towards the coast. When the impact of sand mining reaches the coast there may be an accumulated deficit in available river bed material corresponding to several decades sediment supply from the catchment. This means that an immediate halt in the sand mining will have hardly any remedial effect on the supply of sand to the coast, as the entire river bed has to rebuild before the original supply is re-established.
Sand mining close to the river mouth causes an immediate decrease in the supply of sand to the coast, and halt of the sand mining in this situation will quickly cause recover of the supply of sand to the coast.
These impacts of sand mining on coastal sediment supply are observed in many rivers, for example for rivers in Sri Lanka [14]. Coastal erosion is not the only impact of river sand mining. Other impacts also have to be taken into consideration:. Hence, river sand mining requires an integrated approach taking into account all the impacts. This calls for close collaboration between river authorities and coastal authorities.
Small sandy bays enclosed between headlands have in general a crescentic shape, which is due to wave diffraction at the headlands and wave refraction in nearshore shallow water see Shallow-water wave theory. However, the shape and position of the shoreline depends not only on the wave climate, but also on sand supply to the bay.
There are two possible sources see Fig. The overall transport mechanisms in a crescent-shaped bay can be characterised as follows. The supply of sand from the upstream bay Q B will pass the headland and cross the bay via a bar.
If a river also contributes Q R to the littoral budget, this material will be transported downdrift into the bay, partly along the shoreline and partly onto the bar. The shape of the crescent-shaped bay is stable, apart from seasonal variations, as long as the supply of material to the bay Q S1 is not changed. This means that human interventions, which cause changes in one bay will gradually penetrate into the downdrift bays.
Hence, crescent-shaped bays, although they appear fairly stable, are actually very sensitive to interventions that modify the supply of sand. Wakes from fast ferries cause shore degradation in sheltered coastal environments [15] [16]. The special wake generated by fast ferries is characterised by a series of approximately 10 relatively low waves significant wave height below 1 m , but relatively long waves.
These wake waves are very similar to swell waves and they are exposed to considerable shoaling when approaching the coast. They often break as plunging breakers. If a fast ferry navigates through protected waters, the wake waves are very different from the natural waves along the navigation route. The wake waves caused by fast ferries may influence coastal conditions in the following ways:. A precondition for approval of a new fast ferry route is therefore to perform an environmental impact assessment study [17].
This will often result in navigation restrictions for certain parts of the route. An example of the impact of such waves is presented in Fig. Note the violent breaking, turbid water and rip currents.
The mining of sand and gravel along beaches and in the surf-zone will cause erosion by depleting the shore of its sediment resources. In connection with maintenance dredging of tidal inlets, harbours, and navigation channels, sand is very often lost from the littoral budget because the sand, unless otherwise regulated by legislation, is normally dumped at deep water.
Coral mining and other means of spoiling the protective coral reefs, for example, fishing by the use of explosives or pollution, will also cause coastal erosion and beach degradation. The protective function of the reef disappears and the production of carbonate sand stops. In conclusion, it can be seen that nearly every type of development and coastal protection along a littoral shoreline or along rivers will result in erosion of the adjacent shores and coasts. Log in. Page Discussion. Read View source View history.
Jump to: navigation , search. Article reviewed by. Job Dronkers See the discussion page. Shoreline management guidelines. Coastal erosion and control.
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