Delta Barrages
The Delta Barrages , now colloquially known as the Mohamed Ali Bridges , are two dams over the Rosetta Arm and the Damietta Arm of the Nile immediately after the river branches off into the Nile Delta, about 20 km below the center of Cairo in Egypt .
Erected in the mid-nineteenth century, these structures were the first dams ever built over the Nile. They served to improve agriculture in the Nile Delta and initiated the transition from the seasonal irrigation in flood basins, used since the Pharaohs, to year-round irrigation through canals, which made several harvests a year and for the first time the cultivation of cotton possible.
Since the completion of the Muhammad Ali Barrages , which were built in sight downstream to relieve them, in 1937, the Delta Barrages have only served as a tourist destination. They are standing with open gates and locks in the reservoirs of the more modern facility and are therefore no longer fully visible.
Surname
The dams were built from the beginning and are still known today with the French word barrages , as both the first draft and the later project were created and executed by French people working for the Egyptian building authorities. The name Delta Barrages was retained by the British when they later took control of Egypt.
Delta Barrages
The Delta Barrages are straight, brick dam walls with a height of 13.75 m above the foundation plate. The wall over the Rosetta Arm ( 30 ° 11 ′ 4 ″ N , 31 ° 7 ′ 0 ″ E ) has a length of 465 m, the wall over the Damietta Arm ( 30 ° 11 ′ 35 ″ N , 31 ° 7 ′ 43 ″ O ) is 535 m long, but a longer part of it stands on the foreland. A 5 m wide road leads over the two 10 m wide dam walls, which today is only reserved for the often numerous pedestrians. Archways with battlements and towers form the entrances to the dams, while similar structures stand in the middle of the two dams.
Both Delta Barrages have 61 archways that are 12.25 m high and 5 m wide, with the exception of two 5.5 m wide arches near the middle of the river. The wall over the Damietta arm was originally supposed to have 71 arches, but the 10 arches that would have stood on land were abandoned.
The iron gates, which no longer exist today, were supposed to remain open during high tide, but closed during low tide in summer, in order to automatically keep the water level 4.5 m above the lowest level with a complicated mechanism, which, however, never reached for technical reasons not even when the gates were replaced by simple constructions in a later renovation.
Locks with around 12 m wide chambers were used for shipping.
The two dams are connected by a road embankment that leads over the inlet structure of the Minufiya Canal, which consists of a dam with 9 arches and a lock.
Above the dams, on the left, western bank of the Rosetta Arm, there is the inlet structure to the Buhaira Canal and on the right, eastern bank of the Damietta Arm, the inlet structure to the Tewfiki Canal, built in 1889, both of which are also provided with bridges and locks.
history
Muhammad Ali Pasha , who introduced various innovations and reforms during his rule over Egypt from 1805 to 1848 , also pushed for the development of agriculture in the Nile Delta. This has always depended on the annual Nile flood between July / August and October / November being sufficient to irrigate fields that are unfavorable or too high. The cotton , which was coveted as a novelty at the time , could hardly be grown because it was not allowed to stand in water and had to be constantly and adequately irrigated in higher fields during its longer growth phase.
First draft by Linant de Bellefonds
Muhammad Ali had already ordered the Rosetta Arm to be filled in so that the agriculture on the Damietta Arm could be adequately irrigated in the summer. Linant de Bellefonds , whom he had hired to modernize the irrigation systems in Upper Egypt and who had just been promoted to director of the administration of the canals, bridges and roads in all of Egypt, was able to dissuade him when he suggested closing dams with locks over both arms of the Nile instead to build. The Nile should be able to flow freely through the opened gates during the great floods. In the arid summer, however, it should be dammed up to such an extent that its water could alternately be directed through adjustable weirs into one of three higher-lying canals, thus ensuring longer periods of irrigation in almost the entire Nile Delta.
Muhammad Ali ordered Linant to begin preparations for the project immediately. He should use the stone blocks of the pyramids for the dam walls. Linant knew there was no contradiction. He therefore made a detailed, complex calculation, from the results of which Muhammad Ali himself was able to deduce that new stone blocks from the quarry would be more cost-effective than using the blocks from the pyramids.
Construction, estimated to take five years, began at the end of 1833, but was interrupted for several months in 1835 by a plague epidemic. After that, the construction site couldn't get going again due to a lack of labor and material deliveries. Linant was promoted to the Ministry of Construction, where he was entrusted with other tasks. Muhammed Ali had lost interest in the project, so he finally had it discontinued.
Design and construction by Eugène Mougel
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A few years later, Eugène Mougel , a French hydraulic engineer working on port structures in Alexandria, was able to convince Muhammed Ali to have a similar design of the dams carried out a little higher up than the one made by Linant.
In June 1847 construction began on the Rosetta Barrage. The great temporal pressure exerted by the ruler and which Mougel did not dare to oppose led to the dams being built on insufficiently solid foundations. The time of death of Muhammed Ali in 1848, the work was far from finished, not even in 1854 when Muhammad Said succeed Abbas I took.
Muhammad Said was fascinated by the idea of converting the canal system and the dams into a defense system against possible attackers from the north, and therefore had the arches built with battlements and towers, which actually had little military value.
The dams were declared ready in 1861, but when the first attempt to dammed water was made two years later, cracks and washouts appeared. In 1867, part of the Rosetta Dam was even moved a few centimeters downstream. The dams were therefore only used for damming 1.5 m. Numerous reports came to the conclusion that the walls were built solid, but on poor foundations. It was therefore questioned whether they would ever be usable and it was even suggested that the dam walls should be abandoned for good and that the Nile Delta be irrigated entirely with steam-powered pumps, which have now become cheaper.
Remedial measures
After the British had also taken over the management of the irrigation office with the rule in Egypt in 1882 , after careful investigations they came to the conclusion that they would dare to renovate the building. In the low water periods from 1887 to 1890, half of a dam wall was cordoned off with a coffer dam and drained in order to then strengthen and significantly widen the base plates from the outside. This was to prevent the water from finding a way under the dams. Precise observations over the next few years seemed to confirm the success of the measures, but some springs in the river bed below the walls continued to cause concern.
In the years 1896 to 1898 the foundations were therefore reinforced with mortar injections. A total of 12,400 m of vertical boreholes were driven from the carriageway through the pillars of the archways, in which 6,094 barrels of mortar created the necessary pressure under their own weight to fill in some considerable cavities in the foundations, so that a stable one after the mortar had set and a waterproof foundation was created.
In 1898 the water in front of the Rosetta Barrage was dammed for the first time to 4.35 meters without any problems. It had already been decided beforehand to install three-meter-wide sleepers with flat ramps and long base plates as additional safety below the dams, as well as appropriate locks to reduce the water pressure on the dams. Since then, the Delta Barrages have always been in the backwater of these thresholds, even at the lowest tide.
Meaning of the Delta Barrages
After the rehabilitation measures, the Delta Barrages were able to damming the Nile regularly by four meters and, via the three main canals and the canal systems connected to them, supply practically the entire delta with water even in summer. The acreage could be increased, but above all the sowing could start earlier and thus cotton and a higher-yielding variety of maize could be grown on a large scale. The cotton harvest doubled to a value of £ 12 million. Three harvests were also possible in certain fields.
It turned out that with the regular filling of the canals, their laborious clearance of silt was hardly necessary, so that the Corvée for this clearing work could be abolished and replaced by paid workers.
The renouncement of the construction of large pumping stations and the significantly lower coal consumption for the operation of the existing pumps brought considerable savings.
Salinisation was largely avoided through the creation of drainage channels and smaller reservoirs with which salt could be washed out of the fields.
The success of the Delta Barrages was so convincing that they served as a model for the dam walls that were soon built in Aswan , Asyut and Zifta .
Muhammad Ali Barrages
In 1935 it became clear that the old dams could not handle any further additions. Therefore, the new Muhammad Ali Barrages were built from 1937 to 1939, with which the water of the Nile can be dammed by 3.8 m in summer.
The dam over the Rosetta Arm ( 30 ° 11 ′ 20 ″ N , 31 ° 6 ′ 34 ″ E ) stands about 830 m below the old Delta Barrage in the middle of the basin created by the bed sill. It is 490 m long and has 46 gates, each 8 m wide, framed by 2.5 m thick pillars. On the left side of the river there is a lock with an 80 m × 12 m chamber.
The dam wall over the Damietta arm with 34 gates was replaced a few years ago by a 64 m wide structure with 9 gates and a lock with a chamber of 90 m × 12 m ( 30 ° 11 ′ 42 ″ N , 31 ° 7 ′ 37 ″ O ). It is located just 200 m below the old Delta Barrage.
See also
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- Major Robert Hanbury Brown: The Delta Barrage of Lower Egypt . National Printing Department, Cairo 1902. Digitized on archive.org
- Angelika Marks: The taming of the Nile - the old "barrages" . In: Das Papyrus Magazin , issue 5, 2012, Cairo. (online at payrus-magazin.de)
- Samir Raafat: The Delta Barrage . In: Cairo Times , August 21, 1997
- Mamdouh Shahin: Hydrology of the Nile Basin. Elsevier, Amsterdam 1985, ISBN 0-444-42433-4 , p. 447 ( excerpts on Google books )
- O. Schulze: The dams of the Nile valley. In: Zeitschrift für Bauwesen, Volume 1, Issue VII – IX, 1900, Sp. 361 ( digitized on digital.zlb.de)
- Fritz Eiselen: Restoration work and new foundations under water with the help of cement grouting. In: Deutsche Bauzeitung, Volume 29, No. 80 of October 7, 1905, p. 483 ( digital copy on kobv.de; PDF, 18.8 MB)
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