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Ash Shuqayq (Saudi Red Sea coast)
is approximately 28 km long and characterised by narrow rocky headlands
with intermittent pocket beaches. Fifty-two sediment samples from six
different environments (beach, dune, sabkha, tidal/lagoon, offshore and wadi)
were analysed. Testing showed that beach and dune sands are mainly medium to
fine grained, with some very coarse sand (MZ = − 0.59ø). Both
beach and dune sands are moderately well to moderately sorted, although some
are poorly sorted due to an influx of wadi sediments. Sediment source
together with littoral reworking contributed to grain size variation.
Carbonate content varied between 1.5% and 23%, whilst the organic content
varied between 1.1% and 13%. Spatial analysis showed increasing southward
carbonate and organic content, with both correlated (r = 0.57).
Sabkha sediments had significantly higher carbonate percentages
(t = 2.898; df = 18; p < 0.01) and results
suggested origins are similar for both UAE Arabian Sea and Saudi Arabian Red
Sea coasts. X-ray diffractions show beach and dune sediments are mainly
composed of detrital quartz and plagioclase feldspar with uncommon amounts of
chlorites. Analysis of sediment characteristics, composition and shoreline
distribution alongside coastal processes, indicate that high chlorite levels
are probably caused by desalination processes. Due to human and ecosystem
health consequences and the likely increased demand for desalination plants,
similar analyses should be undertaken elsewhere, e.g. the Mediterranean.
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The Ash Shuqayq coastline, is located
(between latitudes 17O30` N and 17O45`N) along the Saudi Red Sea coast and
was chosen for Landsat ETM investigations because it is a unique environment,
being characterized by some of the most productive biological ecosystems and
major geological environments (e.g. coastal reefs, mangrove stands, marshes,
sabkhas, alluvial fans, sea cliffs. Landsat ETM data interpretation and
analysis delineated seven major sedimentary environments: recent sediments
sands dunes, sabkhas, sand beaches, lagoons, wadis, organic matter and
vegetation areas. Coloured images from band 4 distinguished between classes
(e.g. soil composition, vegetation, and moisture content) that have certain
common characteristics in the unsupervised classification image. Coastline
bathymetric mapping was undertaken using a mosaic of unsupervised image and
true colour image bands 3, 2 and 1, and false colour images bands 7, 4 and 1,
and 4, 5 and 7. Image interpretation and analysis enabled delineation of the
main geological units: proterozoic rocks extending to the east, a
north-northwest trending belt of Mesozoic to lower Tertiary rocks in the
centre, and a large area of coastal plain (Tihama Plain) of middle Tertiary
to Quaternary deposits. Four water depth zones (<10, 10-20, 20-30 and >30m)
were identified and most of the Ash
Shuqayq coastal area is considered shallow (<10m), although other
deposits in greater water depths (20-30m) were subsequently classified. This
investigation also demonstrated the influence of geology, coastal morphology,
sediment distribution and longshore transport on lowlying rocky and plain
shorelines. Results documented beach geomorphological characteristics, which
tended to be more dissipative and have lower gradient shorefaces, than those
along the most northern part of the study area coastline. Analysis also
demonstrated the valuable contribution Landsat ETM data can make to long-term
coastal management.
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