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NSW Coastline Management Manual

New South Wales Government
September 1990

ISBN 0730575063

Appendix B: Coastline Processes

Appendix B1 - Interaction of Coastline Processes

1 INTRODUCTION

Coastal lands are exposed to never ending attack by the sea, the atmosphere and coastal rivers. The waves, increased water levels and winds associated with storms, together with coastal currents and rivers debouching into coastal waters, reshape beaches and shift beach sediments offshore, onshore and alongshore. At best, a restless equilibrium is achieved with sandy beaches waxing and waning in response to the above forces.

The coastal fringe of New South Wales is an attractive area in which to live, work and play. Over 80% of the State's population live along the seaboard. However, improperly sited, poorly designed or inadequately protected coastal developments are exposed to a variety of coastline hazards. Beach erosion, coastal inundation and wind blown sand can damage or destroy coastal developments and reduce beach amenity.

In order to better manage coastline hazards, it is necessary to understand the various processes that cause them. This suite of appendices describes coastal processes of relevance to the New South Wales coastline:

Before describing these processes, Appendix B2 presents a brief description of the geology of the coastline and continental shelf of New South Wales, and the coastline terminology used in this report.

For reasons of convenience, coastal processes have been largely described on an individual basis in these appendices. However, it is essential to appreciate that they do not operate in isolation, but interact with each other, often in quite complex ways. The purpose of this appendix is to briefly highlight these interactions.

2 INTERACTIONS BETWEEN PROCESSES

Figure B1.1 shows the major processes or manifestations of processes that affect coastal areas. There are five major categories:

Astronomical Processes as manifested in the tidal rise and fall of water levels.
Meteorological Processes winds, storms, rainfall and climate change.
Hydraulic Processes water movement, as manifested in waves,changing water levels and currents.
Sediment Transport Processes sediment movement by water and wind.
Human Activities the use of the coastal zone for different purposes by various groups of the community.
coastal processes

Figure B1.1 Interaction Between Coastal Processes

The first four groups of processes are of a physical nature. They have been studied for many years, and although complex, are now reasonably well understood.

The final group of processes, Human Activities, reflect the many and varied uses of coastal areas by the community and are subject to the economic, political and environmental whims and pressures of our society.

3 EXAMPLES OF INTERACTIONS

Figure B1.1 also shows interactions between the various coastal processes. Significant interactions are shown more prominently. Major potential impacts detrimental to human activities are also highlighted. Three examples serve to illustrate the highly interrelated nature of coastal processes:

First, consider the processes affecting coastal water levels. Water levels are increased by storms (storm surge), rainfall (flood levels in estuaries), the gravitational effects of the planets and moon (tides), climate change (the Greenhouse Effect) and waves (wave setup).

Second, consider wave behaviour. This is the result of storms (generation of waves by wind), currents (refraction of waves), water levels (depth on wave breaking), offshore bathymetry (sediment movement) and human activities (e.g. dredging or breakwaters).

Finally, consider the detrimental impact of coastal processes on human activities. Waves can destroy our coastal structures; elevated water levels can flood coastal developments and erosive sediment transport can wreak havoc on coastal structures and beaches.

In describing the various coastal processes in the following appendices, reference is made to these interrelationships. However, this is necessarily brief and the complex nature of their interactions should be borne in mind when reading Appendix B.