Presentation on theme: "Egypt: The Aswan High Dam The Environmental Impact of the dam."— Presentation transcript:
Egypt: The Aswan High Dam The Environmental Impact of the dam
Background The Aswan Dam is an embankment dam situated across the Nile River in Aswan, Egypt. Since the 1950s, the name commonly refers to the High Dam, which is larger and newer than the Aswan Low Dam, which was first completed in Following Egypt's independence from the United Kingdom, the High Dam was constructed between 1960 and It aimed to increase economic production by further regulating the annual river flooding and providing storage of water for agriculture, and later, to generate hydroelectricity. The dam has had a significant impact on the economy and culture of Egypt.
Before the dams were built, the Nile River flooded each year during late summer, as water flowed down the valley from its East African drainage basin. These floods brought high water and natural nutrients and minerals that annually enriched the fertile soil along the floodplain and delta; this made the Nile valley ideal for farming since ancient times. Because floods vary, in high-water years, the whole crop might be wiped out, while in low- water years widespread drought and famine occasionally occurred. As Egypt's population grew and conditions changed, both a desire and ability developed to control the floods, and thus both protect and support farmland and the economically important cotton crop. With the reservoir storage provided by these dams, the floods could be lessened, and the water could be stored for later release.
Resettlement of People Lake Nasser flooded much of lower Nubia and 100,000 to 120,000 people were resettled in Sudan and Egypt. The majority of the 50,000 Nubians resettled in Egypt were resettled three to ten kilometers from the Nile near Kom Ombo 45 kilometers downstream from Aswan in what was called " New Nubia". Housing and facilities were built for 47 village units whose relationship to each other approximated that in Old Nubia. Irrigated land was provided to grow mainly sugar cane.
The Aswan High Dam, when it was build created Lake Nasser, Lake Nasser Streches back 270 kilometres from the Dam. The Lake has also created alot more land for people to farm on. This is because a lot of water is stored in the lake, and in turn this water can be used to irrigate land around the lake. Lake Nasser has also created a big fishing industry, which produces 25,000 tonnes of fish a year, the fishing industry is aiming to produce 100,000 tonnes by the year 2000.
Unfortunately this dam has caused a big change to the lifes of farmers downstream from the dam. Usually when the river flooded once a year before the dam was built. It deposited fertile soil from upstream on its banks downstream. This washed up soil was extremely furtile, and renewed itself every year at in flood season. But now, since the dam was built the annual flood has been stopped. Causing all the farmers downstream to have to use fertilizers to grow their crops, which makes it more expensive.
The Aswan High Dam is also used to create hydro-electricity for Egypt, In the 1980's this dam was providing half of Egypt's Electricity, but by the 1990's this had fallen as energy demands increased. The electric power capacity of the Aswan High Dam is: 2.1 gigawatts (GW). It consists of 12 Hydro-Generators each rated at 175 MW. Egypt currently has a total installed generating capacity of 16.6 gigawatts (GW) compared to 3.8 GW in 1976, thus the percentage contribution by the High dam has decreased from over half the total electricity generation to less than 13%. This percentage will continue to decrease as more thermal power plants are added. Total capacity expected to be 26 GW by 2010.
Waterlogging and increase in soil salinity Before the construction of the High Dam, groundwater levels in the Nile Valley fluctuated 8-9m per year with the water level of the Nile. During summer when evaporation was highest, the groundwater level was too deep to allow salts dissolved in the water to be pulled to the surface through capillary action. With heavy year-round irrigation, groundwater levels remained high with little fluctuation leading to waterlogging. Soil salinity also increased because the distance between the surface and the groundwater table was small enough (1–2 m depending on soil conditions and temperature) to allow water to be pulled up by evaporation so that the relatively small concentrations of salt in the groundwater accumulated on the soil surface over the years.
Losses due to salinization Since most of the farmland did not have proper subsurface drainage to lower the groundwater table, salinization gradually affected crop yields. A total of 2.1 million hectares thus required subsurface drainage at a cost that exceeded the construction cost of the High Dam. Only 20 years after completion of the High Dam the problem was seriously addressed and a large-scale drainage program was initiated.
Coastal Erosion The High Dam has accelerated erosion of coastlines (due to lack of sediment, which was once brought by the Nile) in Egypt and, according to some sources even all along the eastern Mediterranean. Coastal erosion occurred and efforts to control it were made even before the construction of the High Dam. This erosion may to some extent have been caused by the limited trapping of sediments behind the Old Aswan Dam. The High Dam accelerated erosion and made the construction of further expensive coastal protection works in the Nile Delta necessary.
Health Impact The standing water in irrigation canals is a breeding ground for snails carrying the parasite bilharzia. The incidence of bilharzia increased due to the Aswan High Dam inhibiting the natural fluctuations in water height. Important factors contributing to the prevalence of schistosomiasis were poor sanitation and limited awareness of how the disease was transmitted. Provision of clean water, sanitation, health education and rural clinics has reduced the overall prevalences of schistosomiasis from more than 40 per cent during the pre-dam period to 10 per cent in 1995 and only 2% in 2002.
Reservoir sedimentation Reservoir sedimentation. Sediment deposited in the reservoir is lowering the water storage capacity of Lake Nasser. The reservoir storage capacity is 162 km3, including 31 km3 dead storage at the bottom of the lake below 147m above sea level, 90 km3 live storage, and 41 km3 of storage for high flood waters above 175m above sea level. The annual sediment load of the Nile is about 134 million tons. This means that the dead storage volume would be filled up after 300–500 years if the sediment accumulated at the same rate throughout the area of the lake. Obviously sediment accumulates much faster at the upper reaches of the Lake where sedimentation has already affected the live storage zone. It would take about another 900 years until the live storage zone would be completely sedimented and operation of the dam would become impossible some time before that.
Reservoir evaporation; Aquatic weeds; Pollution from fertilizers Evaporation from Lake Nasser is estimated at 10 km 3 per year, varying mainly as a function of the lake area. While the absolute amount of water lost to evaporation is enormous, it is only 11% of the average volume stored in the Lake and 18% of Egypt's share of the annual flow of the Nile. Before the dam was built, the 50,000 km of irrigation and drainage canals in Egypt had to be dredged regularly to remove sediments. After construction of the dam, aquatic weeds grew much faster in the clearer water, helped by fertilizer residues. The total length of the infested waterways was about 27,000 km in the mid-90s. Weeds have been gradually brought under control by manual, mechanical and biological methods. The increased use of artificial fertilizers has caused chemical pollution which the traditional river sediment did not do.fertilizers
Fishery in the Delta and the Mediterranean Mediterranean fishing and brackish water lake fishery declined after the dam was finished because nutrients that used to flow down the Nile to the Mediterranean were trapped behind the dam. For example, the Sardine catch off the Egyptian coast declined from 18,000 tons in 1962 to a mere 460 tons in 1968, but then gradually recovered to 8,590 tons in A scientific article in the mid-1990s noted that " the mismatch between low primary productivity and relatively high levels of fish production in the region still presents a puzzle to scientist. The Aswan Dam tends to increase the salinity of the Mediterranean Sea, and this affects the Mediterranean's outflow current into the Atlantic Ocean. This current can be traced thousands of kilometers into the Atlantic.
Algae Growth Because of the lower turbidity of the water sunlight penetrates deeper in the Nile water. Because of this and the increased presence of nutrients from fertilizers in the water, more algae grow in the Nile. This in turn increases the costs of drinking water treatment. Apparently few experts had anticipated that water quality in the Nile would actually decrease because of the High Dam.
Irrigated Farmland in Egypt
Dam Specifications The Aswan High Dam is 3,830 metres long, 980 metres wide at the base, 40 metres wide at the crest and 111 metres tall. It contains 43 million cubic metres of material. At maximum, 11,000 cubic metres per second of water can pass through the dam. There are further emergency spillways for an extra 5,000 cubic metres per second and the Toshka Canal links the reservoir to the Toshka Depression. The reservoir, named Lake Nasser, is 550 km long and 35 km at its widest with a surface area of 5,250 square kilometres. It holds 111 cubic kilometres of water.