Egyptian wonder - building Naga Hammadi dam20 September 2007
Imhotep, master builder to the Pharaohs, had the idea for the first pyramid in Eqypt. Today, a new structure is being built on the Nile of similar dimensions, with 400,000m3 of concrete being used to build the Naga Hammadi dam
Master builder Imhotep's first attempt at constructing a unique structure ended in disaster. Under the weight of mud bricks, the 8m high wall collapsed. The material - a combination of mud, straw and strips of fabric - would obviously not suffice for a 60m high structure designed to last for eternity. Imhotep developed a new plan, envisaging a structure built of hewn stone blocks. This marked the birth of building in stone, a method first used 4600 years ago for the pyramid of Sakkara. Imhotep was a man of exceptional imagination. He improved the system of irrigation along the Nile to such an extent that the farmers could water their fields even when the river was low. Imhotep's achievements were to bring him immortal fame, and the ancient Egyptians came to worship him as a god.
Much as today's visitors gaze upon the pyramids with amazement, Imhotep would himself no doubt be impressed at the sight of what his successors are achieving in Naga Hammadi: together with French and Egyptian partners, Bilfinger Berger of Germany is constructing an imposing retaining weir, 340m long at a cost of €300M (US$421M). It comprises a weir with seven gates, each weighing 160 tons, two locks for shipping and a power station with a capacity of 64MW - enough to supply around 200,000 households with electricity. The locks are 17m wide and over 160m in length, sufficient even for the largest tourist vessels that are expected to shuttle between the Temple of Abydos and Luxor. While work continues, the Nile has had to be diverted into an artificial bed, with 6.5Mm3 of soil excavated just for this channel. By comparison, it took 5Mm3 of stone to build the pyramids of Cheops. The 400,000m3 of concrete poured into the weir are enough to fill the Cologne cathedral.
Simply getting the construction materials to this remote site some 700km south of Cairo at the right time represents a notable logistics achievement. The cement comes from Suez, the sand from Luxor and the steel from Alexandria. Great balks of American pine are just being fitted to the lock entrances under the supervision of civil engineer Nathalie Néron - who was possibly the biggest sensation of all for the Egyptian workmen, who were not used to a woman being in charge. 'It took a while for them to get used to me,' says the 25-yearold with an air of confidence, 'but once they did, my crew worked all the better. I only had to threaten to do a job myself, and three of them rushed to do it at once to spare themselves the dishonor.' Néron came to the desert straight from the École Supérieure des Travaux Publics in Paris, and she is proud of her job: 'Even a few years ago, I could never have dreamt of helping to build such an important structure.'
The project is vital for the future of Egypt. The country's problems remain unchanged in principle since Imhotep's time: not even a blade of grass will grow without irrigation. The fertile Nile valley and delta make up just 4% of the land area, but they are home to 97% of Egypt's almost 80M inhabitants. The population is growing at the rate of a million a year. The existing barrages in place between the Aswan Dam and Cairo would not be adequate to meet the demand for water in the next 20 years.
So the engineers at the Ministry of Water Resources did their sums: if the old weir at Naga Hammadi, built by the British in 1930, could be raised by just 1m, irrigation in the hinterland would be vastly improved, creating 3150km2 of new arable land. After three quarters of a century, however, the weir composed of a hundred brick arches was showing its age.
Therefore, the Egyptian government decided to build a new barrage weir 3.5km downstream from the old structure, with the following project goals:
* Build a new structure to replace the existing barrage, making it possible to safely withstand the expected differential head resulting from head pond levels required for irrigation purposes.
* Generate 460GWh of electricity per year.
* Enhance navigation by constructing two navigable locks, large enough to accommodate - in each chamber - two of the largest ships operating on the Nile at the same time.
* Creation of a new road spanning the barrage, with a capacity of 70 tons.
* Creation of employment opportunities in the project area throughout the project execution.
Funding from Europe
When the first engineers arrived to begin a survey of Hammadi a short time later, the local residents gave them an angry reception. It took police protection to persuade the surveyors to venture into an area whose inhabitants have long enjoyed a reputation as stubborn and unwelcoming.
Why should they give up their fertile sugar cane plantations and in some cases even leave their houses, just to make way for a weir? Only when word spread that the Egyptian government would pay generous compensation for the loss of their land did the farmers begin to warm to the plans. In the long term, the retaining weir will help to safeguard the future existence of the population who derive their income mainly from agriculture. In addition, the hydroelectric plant will be a source of much-needed power. An accompanying environmental programme, including the renaturalisation of areas spoiled during construction, has been developed to ensure that this major project sponsored by Germany's Reconstruction and Development Bank (KfW) and the European Investment Bank (EIB) is an all-round development policy success.
Concreting at 50°C
Before work could begin on the weir, it was first necessary to set about diverting the course of the Nile, which flows through Hammadi at an average rate of 45Bm3 per year. The plans called for a 1.3km long diversionary canal on the western side of the river, where the loamy subsoil promised more stability than the sandy soil to the east. In June 2002 the excavators moved in, and day and night 350 trucks hauled the excavated material away to be stockpiled. The 15m deep canal had to withstand erosion, even in flood conditions when the Nile carries up to 1000m3 of water per second. Egyptian workers stitched a synthetic fiber fleece supplied from Germany into long strips and spread it out in the bed of the canal. The Nile was then let into the canal a little at a time to ensure that the fleece did not tear. Finally the old course of the river was blocked with a dam requiring the Nile to flow around the construction site.
But this was where the real challenge began. In the past ten years it has rained once in Hammadi. For all of a quarter of an hour. Then the sun came out again. Outside temperatures in the summer months can reach over 50°C. Laying even a bucketful of cement means working fast. Concrete dries in no time, cracks, crumbles and fails.
Nevertheless, the concrete for the 2m thick base of the weir had to be perfect. As a solution, icemakers were installed next to the mixing plant and chunks of ice were added to the concrete, up to 120 tons every day. Concrete specialists constantly monitored the correct temperature, consistency and composition of the mix. The base slab, power station building and lock walls all needed special mixtures of cement, water and aggregate to suit their particular function. This technical expertise was one of Bilfinger Berger's particular contributions to the joint venture, for which the company sent its experts in concrete technology.
Bilfinger Berger has now almost completed its work. The lock gates and weirs are being erected, the four turbines installed in the power station and the site is slowly being flooded. The inauguration is scheduled for May 2008. Ministers will be on hand, the international sponsors will send representatives to Hammadi, and many of the 3000 men and women who worked on the project will return for the celebrations. Someone from Bilfinger Berger has cast the company logo in concrete and attached it to one of the retaining walls by the inlet to the power station - a few meters below the waterline, naturally. After all, who would want to dispute Imhotep's place in the land of his fathers?
Existing Naga Hammadi Barrage
The Naga Hammadi Barrage is one of three structures on the Nile river in Upper Egypt besides the Aswan and High Aswan dams. It is located near the town of Naga Hammadi some 360km downstream and to the North of Aswan, and was completed in 1930.
Two major side canals branch off from the barrage head pond to the west and east of the barrage. They are over 200 and 150km in length, respectively.
The project consists of a sluiceway structure of masonry arches on a concrete foundation. Its total length is 822m with 100 vents between arches each spanning 6m in width. There are two navigation locks, an old one with a chamber length of 70m and a new one with a chamber length of 157m. Two steel swing bridges cross the downstream heads of the locks.
Gates are double leafed with fixed wheels, each 6m wide, and are moved by two gantry cranes.
Seven bays, each equipped with a 17m wide and 13.5m high radial gate, dimensioned for the emergency discharge of 7000m3/sec. Flap gates on top of the radial gates control outflows up to 650m3/sec simultaneous to power plant releases.
Hydro power plant
Four Bulb turbine units with adjustable blades and a maximum discharge of 460m3/sec each. The total generating capacity of the plant is 64MW, generating an average 460GWh per annum.
Structural length of 217m with a usable chamber length of 170m, 17m in width. Minimum water depth is 3m, maximum lift height is 8m. The minimum filling/emptying time is approximately 11 minutes.
Sandfill between rockfill bunds, the total height above foundation level is 17m. Downstream slope is 1:3, with a crest road width of 9m.
Total cost of the project is approximately €300M (US$421M) distributed as: 54.1% for civil works; 9.8% for hydromechanical works; 28.2% for electric equipment and works; and 7.9% for consulting services.
Main quantities of the civil works
Excavation above and under water (7,100,000m3); backfill (7,100,000m3); filter, rockfill and riprap (730,000m3); plastic concrete diaphragm walls (110,000m3); structural concrete (380,000m3).
Text by Philipp Mausshardt, photographs by Barbara Breyer.
For more information on the project, please contact: Uwe Krenz, Bilfinger Berger Civil, Gustav-Nachtigal-Str. 3, 65189, Weisbaden, Germany. Email: [email protected]TablesCompanies involved