Effects of the Nile damming on Alexandria coastal waters

Effects of the Nile damming
on Alexandria coastal waters
Effets du barrage du Nil sur la qualité des eaux côtières
d’Alexandrie
Mohamed A. Said and Ahmed A. Radwan
National Institute of Oceanography & Fisheries (NIOF), Kayetbay, Al Anfoshy
Alexandria, Egypt
Keywords: Nile damming, coastal waters
Mots-clés : barrage du Nil, eaux côtières
Abstract
The Alexandria region is considered an important, underutilized resource for
agriculture, tourism and industrial activities in Egypt. The main pollution sources
are comprised of domestic sewage, industrial wastes, agricultural runoff through
lake outlets, river discharge, and oil pollution. The effects induced by the Nile
River damming on the physical characteristics of coastal waters in the region have
been investigated.
As a result of the erection of Aswan High Dam in 1965, the last natural discharge
of Nile flood waters into the Mediterranean Sea took place in the summer of 1964.
Furthermore, the annual cycle of the discharge has changed.
The most pronounced and direct effect of the Nile damming is reflected in the
salinity of Alexandria coastal waters, which increased from less than 27 in 1964
before the erection of Aswan High Dam, to around 38 in the Seventies and more
than 39 in 2008. Concurrently, the temperature of surface waters increased by
about 0.62°C/decade over the last 20 years. Overall, the increase in temperature
and salinity with time observed in the coastal waters of the Alexandria region may
be attributed either to anthropogenic modifications, especially the Nile damming,
or to local climatic changes.
Résumé
La région d’Alexandrie est considérée comme une zone où les ressources
agricoles, les activités touristiques et industrielles sont importantes mais sous
exploitées. Les principales sources de pollution sont les rejets d’eaux usées, les
déchets industriels, les polluants agricoles déversés dans les lacs, les rivières et la
pollution pétrolière. Les effets du barrage sur le Nil sur les caractéristiques
physiques des eaux côtières ont été étudiés.
Impact of large coastal Mediterranean cities on marine ecosystems – Alexandria, Egypt 10-12 February 2009
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Le grand barrage d’Assouan a été construit en 1965 et le déversement naturel du
Nil dans la Méditerranée a été interrompu à l’été 1964. Depuis cette date, des
changements dans le cycle annuel de déversement du fleuve ont été observés.
L’effet direct le plus prononcé de la construction du barrage sur le Nil est
l’augmentation de la salinité dans les eaux côtières d’Alexandrie qui est passé de
moins de 27 (en 1964 avant la construction du barrage) à environ 38 (dans les
années 70) à plus de 39 en 2008. En parallèle, la température des eaux de surface
a augmenté de 0.62°C par décade dans les 20 dernières années. De façon générale
(ou globale) l’augmentation de la température et de la salinité avec le temps dans
les eaux côtières de la région d’Alexandrie peut être attribuée soit aux
modifications anthropogéniques (construction du barrage sur le Nil), soit au
changement climatique local.
--------------------
INTRODUCTION
The coastal zone of Egypt on the Mediterranean extends from El-Sallum in the
west to El-Arish in the east for over 1200 km. Alexandria is the largest Egyptian
city on the Mediterranean (more than 4 million inhabitants). It is the main summer
resort of Egypt along the Mediterranean coast. 40% of the nations' industry
surrounds the city from the southern and western borders. Alexandria region
(Fig.1) includes Abu Qir Bay, Rosetta branch of the Nile River, Lake Edku and ElMax Bay. The study area receives various types of pollutants through several landbased sources. The major types of pollution sources are domestic sewages,
industrial wastes and agricultural runoff through Lake Edku, Rosetta Branch of the
Nile River and El-Umum Drain. Industrial wastes include petrochemicals,
fertilizers, textile, dyes and weaving industries, food processing and canning,
power plant, paper and cement industry.
Impact of large coastal Mediterranean cities on marine ecosystems – Alexandria, Egypt 10-12 February 2009
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Longitude (°E)
29.8
29.9
30
30.1
30.2
30.3
30.4
30.5
31.8
31.7
Mediterranean Sea
Latitude (°N)
31.6
31.5
31.4
Abu Qir
Bay
Rosetta
Branch
31.3
Lake Idku
31.2
Alexandria
City
Figure 1. Alexandria region
Consequently, this region is presently facing the problem of water pollution at
some level, which is expected to increase in the future. The aim of the present work
is to study impact of the damming of the Nile River on the water characteristics of
Alexandria region.
MATERIALS AND METHODS
The water discharge from the Rosetta Branch of the Nile River was taken from
Irrigation Department of the Egyptian Ministry of Public Works and Water
Resources (Cairo) during the period 1956-2007. Temperature and salinity data
were taken from all the surveys carried out in the study area (hashed area) during
the period 1964-2008 (Fig. 1).
RESULTS AND DISCUSSION
Before the High Dam, data of the Irrigation Department of the Egyptian ministry of
public works and Water Resources indicated that the average yearly discharge of
the Nile through Rosetta and Damietta branches for the period of 31 years (19121942) amounted to 62 km3 (Gerges, 1976). As a result of the erection of Aswan
High Dam in 1965, the summer of 1964 was the last time for the flood water to
discharge into the Mediterranean. The average yearly discharge for the proceeding
10 years (1956-1965) amounted to 46.93 km3.
Impact of large coastal Mediterranean cities on marine ecosystems – Alexandria, Egypt 10-12 February 2009
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From 1966 on the discharge remarkably decreased. Fig. 2 illustrates the yearly Nile
water discharged to the Mediterranean through Rosette Branch. The average yearly
discharge from 1966 to 2007, i.e. for 42 successive years, amounted to 3.92 km3,
representing about 8% of the average value for the period prior to 1965.
70
60
3
Discharge (km )
50
40
30
20
10
2006
2004
2002
2000
1998
1996
1994
1992
1990
1988
1986
1984
1982
1980
1978
1976
1974
1972
1970
1968
1966
1964
1962
1960
1958
1956
0
Years
3
Figure 2. Yearly Nile River discharge (km ) through Rosetta Branch during the period
1956-2007
Moreover, the annual cycle of the discharge has changed. The discharge usually
occurred from July to August until December or January, the maximum discharge
was observed on september-october with 25 to 30% of the total discharge (Gerges,
1976). At present, the discharge is only through Rosetta, and the maximum is
recorded in winter months. About 65% of the total annual discharge flows into the
sea during the three months of December, January and February. Such a change in
the total amount and pattern of fresh water discharge to the Mediterranean would
certainly affect the physical, chemical as well as the biological conditions of the
south-eastern part of the Mediterranean Sea.
The most pronounced and direct effect of the damming of the Nile River is
reflected on the salinity distribution in the coastal water of the Egyptian coast. The
salinity distribution in this region is characterized by a great complexity due to the
interaction between different factors: the intensive evaporation, the flow of Atlantic
water of low salinity, the existence of Levantine water of high salinity and the river
discharge. The last of these factors is now of a minor value, and hence any
distribution of salinity is controlled by the other factors.
According to Gorgy (1966) and Halim et al (1967), the water discharge from the
Nile caused a rise in sea level at the coast, particularly near the river outlet. The
water slope led to a rise in the horizontal pressure gradient toward the north, which
helped the waters from Rosetta to be moved in a northwest direction and spread by
its own momentum in that direction to an area of about 50 km2 from the outlet,
before being deflected eastward by Coriolis force. Thus the "Nile Stream" was
formed which in its way eastward received more flood water from Damietta and
moved further to the east close to the coast with low salinity. At present, the Nile
water does not cause such a rise in the water level near the coast. As a result, the
horizontal pressure gradients are much less, and the Nile Stream has completely
disappeared.
Impact of large coastal Mediterranean cities on marine ecosystems – Alexandria, Egypt 10-12 February 2009
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Fig. 3 illustrates the long term variation of surface salinity in the coastal water of
the study area (Fig. 1) during 1964-2008. In 1964, the river discharge was the
greatest since 1956, and the surface salinity was very low about 26.675. From 1966
on, a considerable decrease of fresh water discharge was recorded and a
remarkable increase of salinity was observed. The salinity increased from 28.309 in
1966 to around 38 in Seventies and reached >39 in 2008. The temperature anomaly
of the surface water of the study area fluctuated between negative and positive
values with a general trend of increasing to reach 0.62°C/dec during the last 20
years (Fig. 4).
Salinity
40
35
30
2010
2005
2000
1995
Years
1990
1985
1980
1975
1970
1965
1960
25
Figure 3. Long term variation of surface salinity in Alexandria region during 1964-2008
2.2
Temperature Anomaly (°C)
y = 0.0135x - 26.725
1.1
0.0
-1.1
(a)
-2.2
1958
1963
1968
1973
1978
1983
Years
1988
1993
1998
2003
2008
Figure 4. Temperature anomaly of the coastal water of Alexandria region
during 1958 to 2008
CONCLUSIONS
Alexandria region is presently facing the problem of water pollution at some level,
which is expected to increase in the future. The most pronounced and direct effect
of the damming of the Nile River is reflected on the salinity distribution in the
coastal water of Alexandria region. The salinity increased from 26.675 in 1964 to
Impact of large coastal Mediterranean cities on marine ecosystems – Alexandria, Egypt 10-12 February 2009
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more than 39 in 2008. A considerable decrease of fresh water discharge and the
resulting remarkable increase of salinity bring a corresponding change in water
density in the coastal areas, and affect the stability conditions, the mixing processes
and the current system in the area.
During the last 20 years, the temperature of the surface water increased by about
0.62oC/dec. This increase of temperature and salinity of the coastal waters of
Alexandria region with time may be attributed either to anthropogenic
modifications, especially the Nile damming or to local climatic changes.
REFERENCES
Gerges M.A., 1976. The damming of the Nile River and its effects on the
Hydrographic conditions and circulation pattern in the southeastern Mediterranean
and the Suez Canal. Acta Adritiaca, 18: 179-191.
Gorgy S., 1966. Les pêcheries et le milieu dans le secteur méditerranéen de la
RAU. Res. Des Trav. Inst. Peches Marit., 30(1): 25-92.
Halim Y., Guergues S.K. and Saleh H.H., 1967. Hydrographic conditions and
plankton in the South East Mediterranean during the last normal Nile flood (1964).
Int. Revue ges. Hydrobiol., 52(3): 401-425.
Impact of large coastal Mediterranean cities on marine ecosystems – Alexandria, Egypt 10-12 February 2009
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