Abstract
Beach erosion is often associated with sea-level rise, sediment depletion or variation in wave conditions; however above-normal rainfall can cause beach retreat by increasing water-table elevation on the foreshore. On Stanwell Park beach, New South Wales, Australia annual rainfall accounts for 12.4% of the variance in the long-term, high-ride position measured accurately to ±2.5 m for the whole beach using 135 oblique photographs dated between 1895-1980. Sea-level changes account for an additional 4.6%. A 100 mm increase in annual rainfall or a 1 cm rise in sea-level results in 0.79 or 0.44 m retreat respectively of the average high-tide position for this beach. Because of relationships with the Southern Oscillation, initiation of above-normal rainfall periods can be forecast by several months in the Southern Pacific area, The southern Oscillation refers to a fluctuation in atmospheric pressure between the East Pacific and Indo-Australian regions, and has worldwide climatic teleconnections. The worldwide variation in rainfall and sea-level for the period 1960-1979 was accessed using information from NOAA and Permanent Service for Mean Sea Level tapes. There is far more information on rainfall characteristics than on sea-level changes. Results indicate that sea-level has not risen uniformly worldwide in the last two decades; it has fallen in Western Europe and western North America. Most stretches of world coastline where rising sea-level has traditionally been invoked to account for beach retreat are also areas where rainfall regimes have become wetter or more variable. The main factor initiating worldwide alterations in rainfall, as well as influencing sea-levels, is the recent shift in climate since 1948 when, with a cooling globe, rainfall has increased in mid and high-latitudes. Since 1970 meteorological events, including rainfall, have become more variable. In areas with low rates of sea-level rise, changes in rainfall regime may be an important cause of beach change. In areas with a rising sea-level, regime alterations may exacerbate beach erosion.
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Publication Details
Thisarticle was originally published as Bryant, EA, Rainfall and beach erosion relationships, Stanwell Park, Australia, 1895-1980: worldwide implications for coastal erosion, Zeitschrift für Geomorphologie N.F. Supplement 57, 1985, 51-65.