Coastal Landforms

5 Key excerpts on "Coastal Landforms"

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  eBook - ePub

  Landscape: Pattern, Perception and Process

  • Simon Bell(Author)
  • 2012(Publication Date)
  • Routledge

    (Publisher)

  Coastline Patterns Wave action creates the coastlines with their highly complex fractal structures of cliffs, caves, stacks and wave-cut platforms. The composition of the rock, whether soft and easily eroded or hard and resistant, or the manner and direction of its bedding, partly determine the pattern of the coastline and the character of its structures. Tilted bedding of larger rocks of different types and strengths may result in a series of ridges containing rock pools, whilst horizontal bedding can lead to vertical cliffs. Weaknesses in some rock layers leads to undercutting and collapse, leaving stronger sections, which are then eroded further.

  The pressure of water and air in the waves thrown against cliffs helps to erode concave sections into caves. The intervening convex sections can become promontories and are eventually eroded away by the expansion of the caves (Figure 6.11 ). Lower strata may erode leaving higher sections intact and producing arches or natural bridges, which subsequently collapse leaving a rock tower or stack out at sea. The coastal edge thus describes a series of meandering shapes while the development of bays and promontories relates to aspects of explosion patterns and their outward spread, as described in Chapter One.

  All this leads to the highly fractal nature of coastlines with many microhabitats between high and low water for marine wildlife to use. The diversity displayed by the range of sizes of coastal structures and the habitats created by the different rock types and evolving structures make these some of the most aesthetically attractive landscapes. Their wildness, the force of the elements (wind, waves, tides and storms) also make it a dynamic landscape. Artists have always been drawn to coastal landscapes. Even in heavily urbanized areas, coasts give an immediate sense of wildness and closeness to wilful and uncontrolled nature, so that sublime emotions can be felt. The power of the forces at work is so great that attempts to control them with artificial defences usually fail, unless they respond dynamically to the patterns of erosion.

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  eBook - ePub

  Introduction to Coastal Processes and Geomorphology

  • Gerd Masselink, Michael Hughes, Jasper Knight(Authors)
  • 2014(Publication Date)
  • Routledge

    (Publisher)

  Most early classification schemes are based on the role of sea-level variations, and so distinguish between submerged and emerged coasts (Johnson, 1919). Submerged coasts include drowned river and glacial valleys, termed rias/fjards and fjords, respectively. Coastal plains are characteristic of emerged coasts where sea level has fallen. Shepard (1963) identified primary and secondary coasts. Primary coasts result mainly from non-marine processes and include drowned river valleys, rocky and deltaic coasts. Secondary coasts result mainly from marine processes or organisms and include barrier coasts, coral reefs and mangroves. Coasts can also be classified with respect to their tectonic position (Inman and Nordstrom, 1971). Leading edge coasts, also termed collision coasts, are located adjacent to subducting plate margins such as along the Pacific coasts of South America, Japan and New Zealand. Here, tectonic processes have formed mountain belts that have steep, erosive and rocky coastlines, boulder beaches, and falling relative sea levels. Trailing edge coasts, however, are located away from subducting plate margins, are tectonically benign, older and of lower elevation. Examples are coasts of Africa, Australia and Atlantic coasts of North and South America. These coasts are typically sediment-rich, progradational, with large deltas and sandy beaches. The main shortcoming of these classifications is that they emphasise geological inheritance rather than hydrodynamic processes that shape coastal land-forms. Davies (1980) identified coastal types based solely on wave height and tidal range. Because waves are generated by wind, the distribution of wave environments varies by latitude, reflecting global climate zones (Figure 1.4). Coastlines dominated by storm waves are located in higher temperate and arctic latitudes, whereas swell-dominated coasts are located in lower temperate and tropical latitudes where cyclones (hurricanes) are also important

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  eBook - ePub

  Landscape Grading

  A Study Guide for the LARE

  • Valerie E. Aymer(Author)
  • 2020(Publication Date)
  • Routledge

    (Publisher)

  Section Two

  Landforms

  2.1 What are landforms?

  Landforms are the identifiable shapes that the earth naturally forms due to geological processes. As landscape architects, we mimic and manipulate these basic forms to create functional designs. The natural shapes we are most concerned with are plane surfaces, ridges, valleys, peaks and depressions. These are manifested differently throughout the world and are named by their vegetative and animal habitats. For example, a bog, a swamp, and a fen are different types of wetlands. The processes that form and sustain these different wetlands vary; and the types of bog, swamp, and fen vegetation varies, but the underlying shape they form is a depression, a low point in the topography. It is the underlying landform in all cases that we manipulate in landscape grading. These natural forms are most easily recognized on a larger scale (e.g. 100, 200, 500 scale). However, because these problems are at such a large scale, intricate grading is difficult. Identification of the landforms, knowing where to put the problem elements and calculating slope between contour lines becomes essential.

  2.2 Watersheds

  Together, plane surfaces, ridges, valleys, peaks, and depressions form watersheds. A watershed is a natural drainage basin for a particular area. It carries surface runoff, water from rainfall events, from the highest regions of the watershed downhill until it collects in streams, rivers, ponds, and eventually the ocean.

  Watersheds can be divided into subdrainage basins where water flows to a particular stream or pond within a watershed or they can be linked together to form a larger watershed region. These larger watershed regions are not determined by state government boundaries, but often encompass several states or more than one country. Additional information about watershed processes can be found in the recommended reading. As illustrated in Figure 2.2–1

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  The Early Anglo-Saxon Kingdoms of Southern Britain AD 450-650

  Beneath the Tribal Hidage

  • Sue Harrington, Martin Welch, Martin Welch(Authors)
  • 2014(Publication Date)
  • Oxbow Books

    (Publisher)

  4. Travelling and Using the Land- and Sea-Scapes Coastal erosion and tide patterns In the context of the environmental circumstances of the period AD 450–700, it is important to delineate the potentialities of coastal routeways as they impacted on Early Anglo-Saxon site location and landscape syntax. The coastline of southern England as it exists today was probably broadly in place 3000 years ago (c. 1000 BC) with localised variations thereafter caused by erosion and deposition related to tide and weather patterns. Where different geological formations form the coast, they erode at different rates. Modern estimates suggest that, for the study region’s south coast, the erosion rate will have varied between 28 metres and 108 metres per hundred years. Thus, for example, between Selsey Bill and the mouth of the Cuckmere in East Sussex, the coastline in AD 400 may have been over 1700 metres further out (Goudie and Brunsden 1994, 48, fig. 33). The coast of the Isle of Thanet and north Kent has lost land to a similar extent with estimates of up to 4.8 kilometres for the same period (Brookes 2007, 44). Between Folkestone and Dungeness in southeast Kent, however, the loss seems to have been far less, estimated at approximately 400 metres. There are two consistent factors in coastal formation (Cresswell 1959): tide rotation and wave fetch. Wave fetch refers to the distance a wave travels before it hits the shoreline and, as Figure 12 (derived from Cresswell 1959, 21) shows, the greatest impact is of the Atlantic Ocean onto the west coast of the British Isles. Correspondingly, the shortest fetches occur across the Irish Sea and along the English Channel. The North Sea is an area of medium fetch, with the break point between this and the short-fetch waves of the English Channel found around the North Foreland in Kent, indicating contrasting maritime conditions along each of these coasts

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  Coastal Ecosystem Processes

  • Daniel M. Alongi(Author)
  • 2020(Publication Date)
  • CRC Press

    (Publisher)

  471 Considering the large temporal and spatial variations characteristic of tidal estuaries, bays, and lagoons, it would be ironic indeed if the long-term predictability of such changes is one of the major factors driving the high fisheries yields in the world’s coastal zones.

  FIGURE 6.9The relationship between primary production and fisheries yield for different aquatic environments. (Adapted from Day, Jr., J. W. et al., Estuarine Ecology, John Wiley & Sons, New York, 1989, 558.)

  6.6 COASTAL LAGOONS (TYPE VII)

  The primacy of wave energy separates coastal lagoons from tidally dominated lagoons and other coastal systems under Dronker’s classification’n (Table 6.1 ). An excellent book has recently been published on coastal lagoon processes,472 so much of the discussion which follows is abstracted from various chapters contributed to the volume. A practicable definition of a coastal lagoon is472

  A shallow water body separated from the ocean by a barrier, connected at least intermittently to the ocean by one or more restricted inlets, and usually oriented shore-parallel.

  Worldwide, coastal lagoons occupy by area approximately 13% of the coastal zone and include large water bodies, such as the Baltic Sea and the Wadden Sea in Europe. Physical processes within lagoons are greatly influenced by:

  • Catchment size

  • Water depth

  • Inlet size and configuration

  • Orientation with respect to prevailing winds

  Advective transport regulates lagoonal circulation balanced by precipitation, evaporation, groundwater seepage, and surface runoff. Seasonality is induced by wet and dry seasonal changes, higher evaporation in summer, and temporal changes in wind direction. Tides are important mainly near inlets, but residual tidal flow can be important in the long-term; however, advection in response to local wind forcing is usually dominant. For these reasons, most coastal lagoons accumulate organic and inorganic materials, including sediments, and serve as material traps. These processes greatly influence the structure and energetics of food webs, including nutrient dynamics and mass balances. Occasionally, I will violate Dronker’s distinctions412

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