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. 1
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 El- Max 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. 2
31.8 Longitude ( E) 29.8 29.9 30 30.1 30.2 30.3 30.4 30.5 31.7 Mediterranean Sea 31.6 Latitude ( N) 31.5 31.4 31.3 Abu Qir Bay Rosetta Branch 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 (1912-1942) amounted to 62 km 3 (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 km 3. 3
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 km 3, representing about 8% of the average value for the period prior to 1965. 70 60 50 Discharge (km 3 ) 40 30 20 10 0 1956 1958 1960 1962 1964 1966 1968 1970 1972 1974 1976 1978 1980 Figure 2. Yearly Nile River discharge (km 3 ) 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 km 2 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. 1982 Years 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 4
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). 40 Salinity 35 30 25 1960 1965 1970 1975 1980 1985 Years 1990 1995 2000 2005 2010 Figure 3. Long term variation of surface salinity in Alexandria region during 1964-2008 2.2 y = 0.0135x - 26.725 Temperature Anomaly ( C) 1.1 0.0-1.1 (a) -2.2 1958 1963 1968 1973 1978 1983 1988 1993 1998 2003 2008 Years 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 5
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. 6