Introduction

In previous chapters we saw that NWP is an initial/boundary value problem: given an estimate of the present state of the atmosphere (initial conditions), and appropriate surface and lateral boundary conditions, the model simulates (forecasts) the atmospheric evolution. Obviously, the more accurate the estimate of the initial conditions, the better the quality of the forecasts. Currently, operational NWP centers produce initial conditions through a statistical combination of observations and short-range forecasts. This approach has become known as “data assimilation”, whose purpose is defined by Talagrand (1997) as “using all the available information, to determine as accurately as possible the state of the atmospheric (or oceanic) flow.”

There are several excellent reviews of this subject, which has become an important science in itself. The book Atmospheric data analysis by Daley (1991) is a comprehensive description of methods for atmospheric data analysis and assimilation. Ghil and Malanotte-Rizzoli (1991) have written a rigorous discussion of present data assimilation methods with special emphasis on sequential methods. Talagrand (1997) gives an elegant introductory overview of current methods of data assimilation, and Zupanski and Kalnay (1999) also provide a short introduction to the subject. The book Data assimilation in meteorology and oceanography: Theory and practice (Ghil et al., editors, 1997) contains a wealth of important papers on current methods for data assimilation. An earlier but still useful book is Dynamic meteorology: Data assimilation methods (Bengtsson et al., editors, 1981). Thiebaux and Pedder (1987) provided a description of spatial interpolation methods applied to meteorology.

During the 50 years of numerical weather prediction the number of textbooks dealing with the subject has been very small, the latest being the 1980 book by Haltiner and Williams. As you will soon realize, the intervening years have seen impressive development and success. Eugenia Kalnay has contributed significantly to this expansion, and the meteorological community is fortunate that she has applied her knowledge and insight to writing this book.

Eugenia was born in Argentina, where she had exceptionally good teachers. She had planned to study physics, but was introduced to meteorology by a stroke of fate; her mother simply entered her in a competition for a scholarship from the Argentine National Weather Service! But a military coup took place in Argentina in 1966 when Eugenia was a student, and the College of Sciences was invaded by military forces. Rolando Garcia, then Dean of the College of Sciences, was able to obtain for her an assistantship with Jule Charney at the Massachusetts Institute of Technology. She was the first female doctoral candidate in the Department and an outstanding student. In 1971, under Charney's supervision, she finished an excellent thesis on the circulation of Venus. She recalls that an important lesson she learned from Charney at that time was that if her numerical results did not agree with accepted theory it might be because the theory was wrong.

Previous chapters have described coastal landforms and discussed morphodynamic frameworks for interpreting the pattern of adjustments for different coastal types. The range of adjustments is complex and individual coasts change at varying rates and in varying directions. The level of uncertainty about what will happen in the future increases as the time scale increases. Although coastal landforms and the natural processes of erosion and deposition that shape them are the focus of this book, this natural pattern of adjustment is increasingly influenced directly and indirectly by human activities. Many coasts have been substantially modified by local structural and ecological changes brought about intentionally or unintentionally by humans. The impact of human activities can be felt beyond the local scale. Climate change as a result of the enhanced greenhouse effect and the associated threat of accelerated sea-level rise imply human impact on a global scale at an unprecedented rate. These impacts are added to natural pattens of change.

No coast is now likely to be beyond the influence of humans who have become a force ‘as powerful as many natural forces of change, stronger than some and sometimes as mindless as any’ (Meyer, 1996, p. 2).

This chapter is concerned with coral reefs and associated carbonate environments on tropical and subtropical coasts. Reefs are dynamic geomorphological systems demonstrating a complex interplay between physical and biological processes. They form solid limestone, simultaneously producing, breaking down and redistributing sediments of different sizes to construct a range of landforms. As a result of their ability to build rigid, wave-resistant structures, corals modify the environment in which they live, as expressed by Darwin in the quotation above. Reefs contain a variety of interacting subsystems operating over a broader range of time scales than generally seen on rocky coasts, comprising construction, destruction and various responses to extreme perturbations, such as storms.

Deltas and estuaries are dynamic systems associated with the mouths of rivers. Deltas are accumulations of river-derived sediment whereas estuaries are the tide-influenced lower parts of rivers and their valleys. The distinction between them is sometimes difficult to discern, and it is useful to consider a continuum of deltaic–estuarine landforms. Deltaic–estuarine morphology is influenced by geological setting and topography, and landforms are shaped by hydrodynamic processes. Riverine and coastal sediments are affected by both alluvial and marine influences, together with minor local processes, such as direct input of colluvium from hillslopes, cliff retreat, wind redistribution of sediment, and chemical and biological action.

River discharge and the rate of delivery of sediment to the ocean or embayment vary in relation to catchment size, lithology and climate (Milliman, 2001). The rivers that drain from the continental area of southern and eastern Asia, with highly tectonic hinterlands and prominent monsoon climates, for instance, deliver large volumes of sediment to the oceans (Milliman and Meade, 1983). However, steep, tectonically active island catchments, such as those throughout the Indonesian island arc, also contribute disproportionately large sediment volumes to the ocean (Milliman and Syvitski, 1992).

This book outlines the way that coasts operate. It is written for students of coastal geomorphology, coastal environments, and coastal geology, and for all those with an interest in coastal landforms or who seek insights into the way the coast behaves. It brings together studies of process operation and studies of coastal evolution concerned with longer-term landform development, into morphodynamic models. Coastal morphodynamics involves the mutual co-adjustment of process and form. It provides a framework from which to generalise across space and time scales. The book introduces these concepts and outlines geological setting, materials and coastal processes. Although there are physical principles which govern the response of sediment to forcing factors such as wave energy, the complexity of non-linear interactions means that it is generally difficult to scale up to explain behaviour over time scales that are relevant to human societies.

The book is based heavily on my own research experiences in Australia, Britain, the United States, New Zealand and on many islands in the West Indies, Pacific and Indian Oceans. It also draws extensively on the scientific literature and pays particular tribute in terms of historical perspective to those coastal scientists who have built the foundations of what we know. I hope that it instils something of the sense of wonder that I feel about the coast, and offers new perspectives on how the coast is shaped.

Coasts are often highly scenic and contain abundant natural resources. The majority of the world's population lives close to the sea. As many as 3 billion people (50% of the global total) live within 60 km of the shoreline. The development of urbanised societies was associated with deltaic plains in semiarid areas, and the first cities appeared shortly after the geomorphological evolution of these plains (Stanley and Warne, 1993a). The coast plays an important role in global transportation, and is the destination of many of the world's tourists.

The shoreline is where the land meets the sea, and it is continually changing. Coastal scientists, and the casual ‘wanderer by the shore’, have attempted to understand the shoreline in relation to the processes that shape it, and interrelationships with the adjacent shallow marine and terrestrial hinterland environments. Explaining the geomorphological changes that are occurring on the coast is becoming increasingly important in order to manage coastal resources in a sustainable way.

This book examines the coast as a dynamic geomorphological system. Geomorphology is the study of landforms, and coastal geomorphology is concerned primarily with explaining the many different types of coastal landforms, and understanding the factors that shape them.

Beaches represent some of the most dynamic coasts; they are attractive, not only from aesthetic and recreational points of view, but also as field areas for geomorphological research. The term beach describes wave-deposited sediment. As sediments continue to accrete on beaches they build a larger feature much of which is no longer actively reworked by waves, termed a barrier.

Coastal landforms adjust towards, but rarely find, delicate and dynamic balances with the processes that operate. This is expressed very clearly in the above quotation from G.K. Gilbert, and has been a recurrent theme in the preceding chapters.

Rocky coasts occur where rugged or relatively resistant terrestrial lithology abuts the ocean, forming a distinct or abrupt transition between land and sea. They are typically high-energy coasts, primarily of sea cliffs and other steeply inclined shorelines, on which the influence of underlying rock type is plainly apparent. Many of these coasts evolve at slow rates; in places, resistant pre-Tertiary rocks appear to have changed little over millions of years. However, it is clear that tectonic activity and fluctuations of sea level, particularly during the Quaternary, have caused shoreline position to adjust over time.

Coasts composed predominantly of mud, comprising silt and clay-sized sediment, occur in low-energy settings, generally sheltered from wave action. Muddy coasts can be part of, or adjacent to, deltaic–estuarine coasts as described in the previous chapter, and are usually dominated by tides. Fine sediments are transported considerable distances in suspension but if subject to flocculation into low-density deformable aggregates can behave like larger particles. After deposition, muddy sediments tend to be cohesive, making them more resistant to resuspension, and highly organic, supporting a diverse biota.

On muddy coasts, sediments become finer onshore in contrast to beach and barrier coasts which become coarser onshore. Mudflats characterise much of the intertidal zone, but the lower intertidal and subtidal zones tend to contain extensive sandy deposits. The upper intertidal and supratidal zones often support halophytic (salt-tolerant) vegetation, comprising mangroves on tropical shorelines but dominated by salt marshes in mid and high latitudes.

The coastal system operates within a series of boundary conditions. Geological setting and materials exert primary controls on the range of landforms that can be formed by coastal processes. The plate-tectonic setting is important in terms of vertical and horizontal movements over the long-term evolution of a particular coast. Climate affects the rate at which terrestrial and oceanographie processes operate, and is linked to sea-level change. Relative changes of sea level constrain shoreline position and geomorphological process operation, and influence how the coast is shaped at a range of scales. Lithology and the materials from which the coast is composed are also important.

This chapter examines factors that constitute boundary conditions, adopting a geological time-scale perspective, and then examining conditions at increasingly smaller temporal and spatial scales. Plate-tectonic setting influences long-term vertical and horizontal displacements of land relative to sea level. Fluctuations in the level of the sea influence the way in which the land is abraded by marine processes. In some cases, these can be deciphered from terraces or shelves or from sequences of sediments that have been deposited. The significance of sea-level changes at geological time scales, especially through the Quaternary, has been widely accepted.

Coastal landforms are shaped by a range of processes. This chapter examines the principal sources of energy by which these materials are moved. The processes are considered individually, although in practice a stretch of coast is likely to be influenced by several processes, acting simultaneously or in sequence. A modern coastline is the outcome of processes that operate today and those that have operated over time, and many landforms have been partially or wholly inherited from former conditions.

Coastal landforms can be composed of rocks or sediments, as indicated in the previous chapter. The movement of sediment is a primary control on coastal morphodynamics and this chapter begins with a consideration of the sedimentary processes involved with erosion, transport and deposition of this material.

The principal source of energy for most coastal systems comes from waves. The generation of waves and their transformation as they approach the shore are described.