The influence of the trade winds on the coastal development of the Guianas at various scale levels: a synthesis

Abstract

The coastal development of the Guianas is dominated by extensive, shoreface-attached and alongshore westward migrating mudbanks. The behaviour of these mudbanks is mainly determined by a combination of the large supply of Amazon-borne silt and clay and the trade wind generated wave action. In the front zone of the mudbanks, fluid mud is formed. As a result, the incoming waves are strongly attenuated and deposition is favoured. At their rear side, compacted clay deposits are eroded by waves. The mudbanks, migrating in this manner, are the driving mechanism in the development of the smallest coastal unit, which consists of a mudbank and the eastward adjacent interbank area.Eisma et al. [Neth. J. Sea Res. 28 (1991) 181] has demonstrated that the frequency of the northeast trade wind, which blows towards the coast of the Guianas, in the windy season (January till April), shows a systematic change in time. For the period 1953 -1986, there is evidence that the frequency of winds coming from directions between 50j and 80j (roughly eastnortheast) increases. The same applies to the wind velocity from that direction. In the last 10 years a reversal of these trends appears to occur.For a more or less east -west directed coastal section, e.g. the coastline of Suriname, a more easterly direction of the northeast trade wind results in an increased longshore wave energy flux in the coastal waters. This causes an increase in length of the mudbanks, at the detriment of the usually eroding interbank parts of the coast. This is evidenced by the large-scale coastal development during the related period, demonstrating an increasing length of the mudbanks and consequently an increasing net accretion. It is hypothesised that this development will reverse if the new trends in wind direction and velocity develop further.At the geological scale, it is considered that a coincidence of a systematic increase of more northerly directed wind frequencies and a fall in sea level are responsible for the two erosive interruptions in the generally accreting coastal plain during the Young Holocene Period. D

Mangrove trees growing in a very saline condition but not using seawater

“…Since the Holocene, the near-shore marine area has received large deposits of mud derived from the Amazon outflow. 2 Since this time, mangrove forest has developed on the moving mud banks, 3 and the formation of these features over time is controlled by the erosiondeposition processes. 4 A succession of four main types of vegetation occurring on these features in the studied area is given in Fig.…”

Mangroves, mudbanks and seawalls: whose environmental knowledge counts when adapting to sea level rise in Suriname?

“…Augustinus (1978;1980;2004), a physical geographer who has spent much of his career studying the coastal geomorphology of the Guiana coast, provides a scientific explanation of the role that mudbanks play in mangrove ecology. Fine silt and clay particles, originating in the Amazon River, are transported via the Guiana Stream along the northeast coast of South America where they interaction with northeast trade winds and create a system of migrating mudbanks that dampen wave energy, thus protecting coastal mangroves (Allison et al 2000;Augustinus 2004). Sediments accumulate on the front (west) end of the mudbank and mangroves colonize it when the elevation is high enough with respect to mean high water, where the trees continue to trap sediments (Augustinus and Teunissen 2008).…”

“…Sediments accumulate on the front (west) end of the mudbank and mangroves colonize it when the elevation is high enough with respect to mean high water, where the trees continue to trap sediments (Augustinus and Teunissen 2008). As mudbanks move west at a rate of approximately 1.5 km per year, mature mangrove forests become exposed to undampened waves and collapse (Augustinus 2004). Mudbanks therefore provide primary protection from erosion, while mangroves provide secondary protection because they alone cannot withstand the force of wave energy.…”

“…This is an important deviation of the general scientific explanation of the primary (as opposed to secondary) role of mangroves in coastal protection. Any particular location on the coast may be experiencing land accretion or erosion, in a process that repeats itself about every 30 years (Augustinus 2004) (see Figures 4a and 4b). At the meso scale of several decades, the shoreline is highly variable and can switch relatively suddenly (within a few years) from an eroding to a accreting shoreline depending on the presence or absence of mudbanks.…”

“…At the meso scale of several decades, the shoreline is highly variable and can switch relatively suddenly (within a few years) from an eroding to a accreting shoreline depending on the presence or absence of mudbanks. At the macro scale of decades to centuries, however, the Suriname coast has been found to have a net accretion rate (Augustinus 2004). The 30 year periodicity may change if the northeast trade winds also change direction, which would result in modifications to the general shape of mudbanks (Berrenstein 2010).…”