International Journal of Marine Science, 2017, Vol.7, No.2, 8-18
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1.3.2 Grain size analysis
Grab sampler has been used to collect surface sediment samples from R1, R2, R3 and RB sites. Mechanical
analysis was carried out for the collecting sediments using electrical shakers with series of thieves. Sediments
mean grain size, sorting, kurtosis and skewness were estimated and calculated using the grain size statistics
program GSSTAT version 2.04 manufacture by USGS science for a changing world.
2 Results and Discussion
The construction of Aswan High Dam was completed in 1968. It resulted the low flow released from Edfina
Barrage to the end of Rosetta branch, which is not able to push the sediments away from the estuary (Frihy, 1996).
As a result, the sediment deposits inside the estuary as spit. The case where the discharge from the estuary is
negligible, the deposited material succeeds to close the outlet. This case is already happened at Slapton Ley and
Low Pool in the South West Peninsula of England (Kidson, 1972).
To understand the temporal and spatial variation of the spit, satellite images presented by Google Earth program
have been used. Six successive images of Rosetta Estuary during different periods starting from February 2007 to
September 2015 were investigated. Figure 2 (A-F) illustrates that the spit was formed already inside the Rosetta
Estuary. It can be observed that the Rosetta Estuarine spit migrated toward the riverside. This indicates that
Rosetta Estuarine environment is an extremely dynamic. Similar observations are also made by Weitkamp (1994).
Figure 2 Google Earth images of spit migration from February 2007 to September 2015 at the Rosetta Estuary
Rate of spit migration is estimated from the analysis of historical images and field measurements (Figure 2). The
Google earth ruler option has been used to measure the distance between the locations of the successive spits.
Regression analysis has been carried out for estimation of the spit migration rate and it revealed positive linear
trend with 0.0005 slope. The calculated value (0.9587) of the coefficient of determination (R
2
) indicated high
correlation between the displacements of the spit with the time. The analysis indicated that the displacement of the
spit was about 1.5 km during 8 years with rate of about 187 m/y (Figure 3). Actually, during the 8 years study, that
rate varied inter annually depending on the variations in wave characteristics, river discharge. This is in agreement
with the finding of Anthony (2015).
2.1 Evolution of Rosetta Estuary spit
Two spits at the Rosetta mouth were identified during 1986-1993 (Frihy and Lawrence, 2004). The two small spits
protrude toward the main entrance of the Nile from both sides of the Rosetta inlet attached to the shore at one end,
and extend parallel to the coastline for 0.6 km and relief of 0.5m above sea level. The platform of the spits
indicated that the western spit was formed from the prevailing longshore current to the east, whereas the eastern
spit was associated with the local reversal of the prevailing current to the west.
