Yasser Metwally

My life…and the world

The High Dam of Egypt

The author: Professor Yasser Metwally

http://yassermetwally.com


Located near Aswan, the world famous High Dam was an engineering miracle when it was built in the 1960s. It contains 18 times the material used in the Great Pyramid of Cheops.  The Dam is 11,811 feet long, 3215 feet thick at the base and and 364 feet tall. Today it provides irrigation and electricity for the whole of Egypt and, together with the old Aswan Dam built by the British between 1898 and 1902`, 6km down river, wonderful views for visitors. From the top of the two Mile long High Dam you can gaze across Lake Nassar, the huge reservoir created when it was built, to Kalabsha temple in the south and the huge power station to the north.

The High Dam created a 30% increase in the cultivatable land in Egypt, and raised the water table for the Shara as far away as Algeria.  The electricity producing capability of the Dam doubled Egypt’s available supply.

The High Dam added an whole new aspect to Egypt, and a new environment as well.  The lake is some 500 miles long and at the time it was built, if not now, was the world’s largest artificial lake.

Aswan high dam ...Click to enlarge

Figure 1. Aswan high dam

  • The Importance of the Aswan High Dam

What is the Aswan Dam, why is it needed and why is it one of the must-see sites in Egypt? The dam is named after Aswan, the city on the first cataract of the Nile River in Egypt. There are actually two dams in Aswan, the newer Aswan High Dam and the older Aswan Low Dam.

  • The Flooding of the Nile River

Understand that both dams exist because of the Nile River. The purpose of the dam is to prevent the Nile River from flooding, to harvest water for agricultural purposes and to generate electricity.

Even if you took water and electricity out of the equation, the Nile River would flood every year during summer months because of waters from East Africa steadily flowing down. This has been a natural phenomenon ever since ancient times. Back then, floods were nothing to be concerned of. They actually brought more nutrients and minerals to soil, which made land around the Nile River fertile for farmers.

However, as the population grew, mankind saw the need to control these heavy waters, otherwise, the overflow would start to damage the fields. The results of flooding today are devastating. In a year with very high waters, an entire crop might be completely destroyed. Even in a year with low waters, there are many instances of drought and famine.

Location of Aswan high dam ...Click to enlarge

Figure 2. Location of Aswan high dam

  • The Size of the High Dam

The Aswan High Dam is 3,830 meters in length, 980 meters wide at the base, and 111 meters tall. The dam contains 43 million cubic meters of material and moves 11,000 cubic meters of water every second.

There are also emergency spillways built in, as well as a canal (Toshka) that links the reservoir to the Toshka Depression. This gives you some idea of the power of the Nile River. Imagine that power uncontrolled! Now you see why the British people began planning for dam construction as far back as 1889.

Ever since 1967, power generators have been producing hydroelectric output. Today, twelve generators powered by the dam produce about 2.1 gigawatts each.

Aswan high dam ...Click to enlarge

Figure 3. Aswan high dam

When the dam reached its peak performance it produced about half of the entire country’s electricity needs. (Though in recent times it has fallen to less than 15%) Egyptian residents can thank the dam for introducing electricity to many of its poor villages.

The Aswan High Dam is such a massive creation and it has also become a tourist attraction and is included in most Aswan tours.

Slide show 1. The high dam (a satellite view)

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November 26, 2009 Posted by | Modern Egyptian panorama | Leave a comment

The citadel of Egypt

The author: Professor Yasser Metwally

http://yassermetwally.com


Video 1. The citadel of Egypt

Video 2. The citadel of Egypt


References

  1. The Citadel in Cairo [Full text]

November 26, 2009 Posted by | Arabic Egyptian panorama | Leave a comment

Scorpion fish

The author: Professor Yasser Metwally

http://yassermetwally.com


Scorpaenidae, the scorpionfish, are a family of mostly marine fish that includes many of the world’s most venomous species. As the name suggests, scorpionfish have a type of "sting" in the form of sharp spines coated with venomous mucus. The family is a large one, with hundreds of members.[1] They are widespread in tropical and temperate seas, but mostly found in the Indo-Pacific. They should not be confused with the cabezones, of the genus Scorpaenichthys, which belong to a separate, though related family, Cottidae.

  • Varieties

Some types, such as the lionfish, are attractive as well as dangerous, and highly desired for aquaria. In addition to the name scorpionfish, informal names for family members include "firefish", "turkeyfish", "dragonfish", and "stingfish", usually with adjectives added.

General characteristics of family members include a compressed body, ridges and/or spines on the head, one or two spines on the operculum, and three to five spines on the preopercle. The dorsal fin will have 11 to 17 spines, often long and separated from each other, and the pectoral fins will be well-developed, with 11 to 25 rays. The spines of the dorsal, anal, and pelvic fins all have venom glands at their bases.[2]

Most species are bottom-dwellers that feed on crustaceans and smaller fish. Most species inhabit shallow waters, but a few live as deep as 2,200 metres (7,200 ft).[1] Most Scorpionfish, such as the stonefish, wait in disguise for prey to pass them by before swallowing, while lionfish often ambush their prey. When not ambushing, lionfish may herd the fish, shrimp, or crab in to a corner before swallowing. Scorpionfish feed by opening their mouth, then their gills a fraction of a second apart, creating suction. Stripers, grouper, bass, snook, frogfish, toadfish, sculpin, etc., also feed this way, but the scorpionfish, toadfish and sculpins are the only members of this group that have jaw teeth.

Scorpaenid systematics are complicated and unsettled. Fishes of the World recognizes 10 subfamilies with a total of 388 species, while (as of 2006[update]) FishBase follows Eschmeyer and has 3 subfamilies, 25 genera, and 200 species, some of the species being removed to family Sebastidae which other authorities do not follow.

any of the numerous bottom-living marine fish of the family Scorpaenidae, especially those of the genus Scorpaena, widely distributed in temperate and tropical waters. Sometimes also called rockfish, or stonefish, because they commonly live among rocks, scorpion fish are perchlike fish with large, spiny heads and strong, sometimes venomous, fin spines. The fin spines, with or without venom, can produce deep and painful wounds.

Scorpionfish

Figure 1. Scorpion fish

Many scorpion fish are rather dull in colour, but others are brighter—often some shade of red. The largest members of the family grow about 1 m (39 inches) long. Scorpion fish are carnivorous, generally sedentary fish. They often lie quietly on the bottom, and many blend closely with their surroundings by virtue of their colouring and (in some species) a variety of flaps and projections on the head and body. Better-known species include the redfish and the highly coloured, venomous lion-fish.

Video 1. Scorpion Fish being cleaned by Pederson Shrimp

November 26, 2009 Posted by | Underwater photography | Leave a comment

Butterfly fish

The author: Professor Yasser Metwally

http://yassermetwally.com


Butterfly fish, with their amazing array of colors and patterns, are among the most common sites on reefs throughout the world.

Although some species are dull-colored, most wear intricate patterns with striking backgrounds of blue, red, orange, or yellow. Many have dark bands across their eyes and round, eye-like dots on their flanks to confuse predators as to which end to strike and in which direction they’re likely to flee.

Slide show 1. Butterfly fish

There are about 114 species of butterfly fish. They have thin, disk-shaped bodies that closely resemble their equally recognizable cousins, the angelfish. They spend their days tirelessly pecking at coral and rock formations with their long, thin snouts in search of coral polyps, worms, and other small invertebrates.

Some butterfly fish species travel in small schools, although many are solitary until they find a partner, with whom they may mate for life.

November 26, 2009 Posted by | Underwater photography | Leave a comment

Lionfish

The author: Professor Yasser Metwally

http://yassermetwally.com


Pretty much everything about the venomous lionfish—its red-and-white zebra stripes, long, showy pectoral fins, and generally cantankerous demeanor—says, "Don’t touch!"

The venom of the lionfish, delivered via an array of up to 18 needle-like dorsal fins, is purely defensive. It relies on camouflage and lightning-fast reflexes to capture prey, mainly fish and shrimp. A sting from a lionfish is extremely painful to humans and can cause nausea and breathing difficulties, but is rarely fatal.

Lionfish

Figure 1. Lionfish

Lionfish, also called turkey fish, dragon fish and scorpion fish, are native to the reefs and rocky crevices of the Indo-Pacific, although they’ve found their way to warm ocean habitats worldwide.

The largest of lionfish can grow to about 15 inches (0.4 meters) in length, but the average is closer to 1 foot (0.3 meters).

Lionfish.. Click to enalrge

Figure 2. Lionfish

Lionfish are popular in some parts of the world as food, but are far more prized in the aquarium trade. Their population numbers are healthy and their distribution is growing, causing some concerned in the United States, where some feel the success of this non-indigenous species presents human and environmental dangers.

Video 1. Lionfish

November 26, 2009 Posted by | Underwater photography | Leave a comment

Moray Eel fish

The author: Professor Yasser Metwally

http://yassermetwally.com


Diving with Moray Eels: You are finning along a reef with fish swimming all around you when suddenly something makes you stop on your tracks. You see a sight that at once captivates you and implores you to fix your gaze on a head protruding from a hole, seemingly glaring out and opening and closing its jaws in an apparently menacing fashion. You have just spotted a moray eel!

So are they dangerous predators, better to be given a wide berth? If not then why do they seem to adopt such an aggressive appearance? What are the ‘dos’ and ‘don’ts’ of diving with moray eels? Let us take a closer look at this popular reef creature and see what makes the moray so interesting.

Moray Eel fish

Figure 1. Moray Eel fish

  • Distinguishing Features

Moray eels vary considerably in size depending on species, from the ribbon moray at around 25 cm to the giant moray which can be as much as 4 metres in length. Similarly, skin diversity and colour has as many variations as there are species. You can see morays with skin that is speckled, striped, freckled or tattooed, and coloured in a variety of hues including brown, green, off white, yellow, black and blue.

Despite all of these variations it is normally pretty easy to tell when you are looking at a moray eel since their similarities are such that they are not often confused with other marine creatures. Moral eels have a dorsal fin which runs almost the entire length of the body, from the head to the caudal and anal fins, and are made to appear like a snake by their absence of pectoral and pelvic fins.

The head of the moray eel is large with small eyes located quite far forward, and a wide mouth with large teeth for tearing flesh rather than grinding or holding in place. They have a secondary set or toothed jaws in their throat called pharyngeal jaws, which are thrust forward to grab and drag prey down through their digestive system. They are the only known creature to use pharyngeal jaws to grab and hold prey.

There are more than 100 species of moray eel, including the honeycomb (Muraena melanotis), giant moray eel (Gymnothorax javanicus), zebra morays (Gymnomuraena zebra), snowflake morays (Echidna nebulosa), and white eyed moray (Siderea thyrsoidea), Fimbriated moray (Gymnothorax fimbriatus) and the Ribbon eel (Rhinomuraena quaesita).

  • Behaviour

Moray eels secrete a mucus over their smooth skins in greater quantities than other eels, allowing them to swim fast around the reef without fear of abrasion. Also sand-dwelling morays can make their burrow stronger and permanent, as granules adhere with the mucus and attach to the sides of the burrows. There are often parasites on the surface of the moray eel’s skin making them popular with cleaner shrimp and cleaner wrasses.

Due to the small size of the gills, morays have to continuously open and close their mouths in a gaping fashion to maintain a flow of water and facilitate respiration. This is often mistaken as aggressive posturing by the unaware and is part of the reason for the moray eel’s fearsome reputation. Another may be their inability, due to poor eye sight, to distinguish where food ends and where human fingers begin. As well as attacking when under threat, moray eels have been known to bite off and swallow digits of those feeding them.

  • Feeding Habits

Moray eels are carnivores and their diet consists mainly of other fish or cephalopods, as well as mollusks and crustaceans. They go hunting mostly at night and their chief hunting tool is their excellent sense of smell which makes up for their poor eyesight. This means that weakened or dead creatures tend to be easy to detect and are therefore the moray eel’s favoured food.

Otherwise they hide in their crevices waiting until their prey is close enough, and then they launch themselves from the burrow and clasp the prey with their powerful jaws. Their lightning fast strikes are devastatingly impressive, as diver that has seen a moray eel attack will verify.

Moray Eel fish...Click to enlarge

Figure 2. Moray Eel fish

  • Reproduction

Scientific studies have shown hermaproditism in morays, some being sequential (they are male, later becoming female) and others are synchronous (having both functional testes and ovaries at the same time) and can reproduce with either sex.

Courtship among compatible morays begins when water temperatures reach their highest, and they begin sexual posturing in the form of gaping widely. Then the morays will wrap each others’ long slender bodies together, either as a couple or 2 males and a female. They simultaneously release sperm and eggs in the act of fertilisation, which signals the end of their relationship.

  • Life Cycle

On hatching, the eggs take the form of leptocephalus larvae, which look like thin leaf-shaped objects, that float in the open ocean for around 8 months. Then they swim down as elvers to begin life on the reef and eventually become a moray eel, living between 6 and 36 years depending on species in a natural life cycle.

  • Predation

The main predators of moray eels are other moray eels but also large groupers, barracudas and people. In truth this represents very few predators, which explains why they have the confidence to live in burrows or crevices in the reef from which swift flight maybe difficult.

  • Distribution and Habitat

Morays are found worldwide in tropical and temperate seas, particularly in relatively shallow water among reefs and rocks, as well as in estuarine areas.

  • Ecological Considerations

Morays are fished, but are not considered endangered. This is due in no small part to their toxicity. Ciguatoxin, the main toxin of ciguatera, is produced by a toxic dinoflagellate and accumulated up through the food chain, of which moray eels are top, making them dangerous for humans to eat. This fact was apparently the cause of death for King Henry I of England, who expired shortly after feasting on a moray eel.

November 26, 2009 Posted by | Underwater photography | Leave a comment