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The Nile and the Delta

 
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Diorite
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PostPosted: Fri Jun 03, 2005 4:07 am    Post subject: The Nile and the Delta Reply with quote

You know where the word "delta" used for such features comes from, don't you? In case you don't, the Greeks thought the delta of the Nile looked like an upside-down capital delta and they applied that word to the physiographic feature.

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I've read about the water courses in the Delta, and evidently there used to be significantly more than what we see now. I've wondered why that is, and I don't think it would have anything to do with the lowering of the Mediterranean Sea, would it? After all, to the north the Mediterranean is slowly swallowing Venice--the population there is quite alarmed. Or are the two situations completely unrelated, the Delta and Venice?


Much of what ails the Nile delta can be summed up in three words: High Aswan Dam. I'm not sure if you were asking about lower amounts of water coming out of the Nile or the disappearing act the Nile Delta is doing. Both are related to man's impact .

Want the long version? Here goes.

The Nile is an unusual river in a couple of aspects - it flows north (few do - Rhine and Volga, I think, spring to mind) and it has few tributaries that bring in additional water, so that is one of a few in which the amount of the water in the river decreases as you head towards the sea. Most rivers increase in size down-stream. Others that decrease downstream are the Colorado in the west of North America and the Rio Grande upstream of Presidio, Texas.

Damming a river impounds water upstream. For a river like the Nile, this means less water downstream unless the reservoir is full and the gates allow as much water to escape as enters the reservoir. The High Aswan Dam also prevents the annual flood that was the life blood of ancient Egypt. There are now no flood periods to flush and widen channels on the delta. This is added to the fact that much of the water from the river is used. As use goes up, particularly for things like agriculture that don't return water to the river, the amount of water entering the Mediterranean decreases. Alas, there are some people who plan for water usage who think any water in a stream or river is wasted.

The other problem, the disappearing delta, is related to how deltas are formed and how they are maintained. A river brings sediment out to the shoreline and dumps it. Initially, the sediment has a high porosity (there is a lot of open space, just like the space between packed marbles). Over time, as new material is deposited on top, the earlier sediment is compacted - open space is squeezed out. In a natural delta, this is compensated for by flooding. A flood may erode, but on average, at the end of the flood, the river deposits roughly as much material as was eroded. The flood builds up the surface of the delta and keeps it just above sea level. You stop flooding, no more material is put on top of the delta, the delta sinks below sea level (this is part of the problem in Venice, too). Well, the High Aswan Dam stopped flooding, hence the delta is sinking. I believe, too, there is some problem with people using some of the delta mud for things like mud brick as well.

To see the effect, this first link shows a picture of the Nile delta taken from Gemini 4. It shows what the the delta looked like in 1965 before the dam was completed.

http://www.geog.bgu.ac.il/Nasa_epif/gif/hires/g04_01.gif


The other problem with its extent is the other problem Venice is having. Global sea level is rising because the glaciers are melting. The rate of sea level rise double (quoting off of the top of my head) in the last part of the 1900s. Compare the top photo on the site. You will see how the delta has changed, particularly the amount of water now behind the shoreline. I don't think all of the change is sea level rise.

http://www.grida.no/cgiar/awpack/sealevel.htm

Alas, Egypt's agricultural land along the river upstream also suffers from the lack of flooding. The salt accumulating from evaporation isn't being flushed (nor the canals, so disease has increased). The other problem is the lack of new silt. Longer than the Egyptians have had writing, they have been farming the fertile land along the Nile. Almost every year, the Nile replaced the nutrients removed by crops with new silt. The ancient Egyptians didn't have to fertilize, it happened naturally. With the completion of the High Aswan Dam, that natural replenishment stopped. Within 10 years Egypt became one of the biggest users of fertilizer in the world. It's a crime.


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PostPosted: Fri Jun 03, 2005 10:03 am    Post subject: Reply with quote

I really don't think there is a link between the Nile delta and Venice sinking-Venice sinking is due to global warming, the Delta's loss is, as Diorite said, due to the dam.

I remember doing an essay on the effects of the Aswan dam on the Nile. It's pretty terrible. Also, you forgot to mention how the sediment is now filling up the bottom of the reservoir. If this was extracted, it could be used as fertiliser. But it's too expensive to do that, so the reservoir will spread.
Also, remember that that reservoir lake drowned many villages and ancient ruins and monuments. People had to be moved to other towns. Sure Abu Simbel was relocated, but hundreds of other Egyptian monuments weren't
Also, have you heard of 'clear water erosion?' Usually the sediments a river carry cause a lot of erosion, but the Nile now has a lack of this, so the water itself is eroding the land, but no silt is there to replenish this.

The aswan dam was a really bad idea. I know it sounds weird to most, but I think it would be quite an amazing thing to have seen a nile flood. This was a sacred and magical event in ancient times, I mean a flood without rain seemed pretty miraculous to the ancients...and it's such a life giving event, and if it still happens, Egypt's land, monuments etc wouldn't be in such a bad way. Aren't the monuments of Egypt more at risk these days because the water table is rising due to the dam? (I don't know what this thing about the Nile water being salty comes from-is this due to dissolved sediment from the river being concentrated, or from the sea?)

Also, another stupid question. Where does the Nile flood come from? When i first heard about it, I was puzzled as to where all that water came from and it's regularity. I have heard two opinions-one is that it's from the rainy season in Ethiopia, another that it's caused by melting snow from the mountains of central Africa. Which is correct?
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PostPosted: Fri Jun 03, 2005 10:05 pm    Post subject: Reply with quote

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I really don't think there is a link between the Nile delta and Venice sinking-Venice sinking is due to global warming, the Delta's loss is, as Diorite said, due to the dam.


What I meant is that part of Venice's problem is sediment compaction. There is the combination of the compaction causing sinking and the global rise in sea level.

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I remember doing an essay on the effects of the Aswan dam on the Nile. It's pretty terrible. Also, you forgot to mention how the sediment is now filling up the bottom of the reservoir. If this was extracted, it could be used as fertiliser. But it's too expensive to do that, so the reservoir will spread.


And the wider and shallower the reservoir becomes, the more useless it is and the greater the amount of water lost due to evaporation.

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Also, have you heard of 'clear water erosion?' Usually the sediments a river carry cause a lot of erosion, but the Nile now has a lack of this, so the water itself is eroding the land, but no silt is there to replenish this.


Yes, I have. It's a very common problem downstream from dams. The water wants to carry sediment and if it doesn't have any, it will erode to pick it up. So erosion becomes a big problem just downstream of the dam. The change in water quality is also a problem for native species. They were adapted to the original, silt-rich conditions, not clear water.

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Aren't the monuments of Egypt more at risk these days because the water table is rising due to the dam? (I don't know what this thing about the Nile water being salty comes from-is this due to dissolved sediment from the river being concentrated, or from the sea?)


Yes, the water table has risen, damaging the foundations of monuments. The other problem is that the reservoir has increased the humidity in the air, damaging monuments. They've taken more damage from the change in "climate" than they had for hundreds of years before.

As for salinity, it is caused by erosion. When rock is eroded, the rock is broken into smaller pieces and some minerals break down to something stable at the surface. This causes the muddy appearance of water. But along with that, some elements are dissolved into the water. Under normal circumstances, this dissolved material passes downstream and ends up in the ocean, making it salty.

Evaporation in hot, arid climates can increase the salinity in even fresh water because the water leaves, but the dissolved material remains. When the river water is used to irrigate crops, part of the water is used by the plants, but some of the rest of it evaporates, concentrating the dissolved "salts" in the soil. When the river flooded, it would flush these salts from the soil. Without the floods, the salts build up. It would take a tremendous amount of irrigation water to flush the soils. It's not just in Egypt where they have this problem. It is affecting the agriculture in places like the San Joaquin Valley in California and around Pecos, Texas.

Where does the water in the Nile come from? As I understand it, it comes from snow melt in the mountains in the Ethiopian Highlands.

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PostPosted: Sat Jun 04, 2005 3:29 pm    Post subject: Reply with quote

Actually, the Nile splits into two rivers. They are called the "Blue Nile" and the "White Nile". Both supply sediments, but most of it comes from the Ethiopian highland area. The other Nile originates in (I think) Lake Victoria, in Middle Africa.
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PostPosted: Sat Jun 04, 2005 4:52 pm    Post subject: Reply with quote

I still don't get how sediment from Egypt is causing Venice to sink-don't you mean sediment from Italy or nearby? That would make more sense.

I remember watching this programme now, and it said that most of the flood water doesn't come from snow, but from heavy rain falling on Ethiopia, and it fills up a lake there which overflows and this is the major contributor to the Nile flood. Is this correct?
It also said that the sediment comes from eroded volcanic material, which is why the Nile soil is fertile, because volcanic material is very fertile. I'm not sure if that's true, another source says the reason the Nile silt is fertile is because it contains dead plant matter washed in by the rains/snowmelt.

Apparently, I've heard that because of the dam, the Nile water is 'bluer' and clearer than in the past, when it was muddy. I've also heard that the dam has caused climate change in southern Egypt...not sure if that's true but you did mention higher humidity, and that in ancient times (or not so ancient times) the air would have been drier.
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PostPosted: Sat Jun 04, 2005 7:42 pm    Post subject: Reply with quote

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I still don't get how sediment from Egypt is causing Venice to sink-don't you mean sediment from Italy or nearby? That would make more sense.


I'm sorry, I don't seem to be making myself clear. I'm not saying that the sediment from Egypt is making Venice sink. The same process, not the same sediment! Venice sits in a delta/tidal channel environment. Anywhere you have sediment that has been deposited in a delta-type environment it will undergo compacting.

I remember that the Nile has two sources. I think that one supplies more of the water, but I don't remember which one. I know that the Ethiopian highlands are volcanic, so they would contribute that type of sediment. I'm not a specialist in soils, but as I understand it, the best soils are actually a mixture of sediment from different sources.

It's no accident that the great early civilizations sprang up on the flood plains of major rivers - the Nile, Tigris-Euphrates (when it was a little wetter), Huang Ho, Yangtze, Indus, Ganges-Brahmaputra (did I spell that right? Laughing ). Because of the mixed sediment deposited by flooding, the flood plains are very fertile and water is easy to come by, so these are natural places for agriculture to be established.

The Nile is unusual in the fact that the flood was essentially an annual event. This is because of the unique characteristics of the drainage that forms the Nile. Egypt is truly a gift of the Nile.

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PostPosted: Wed Jun 08, 2005 1:07 am    Post subject: Reply with quote

Sorry it took me so long to get around to checking this out, Diorite. You explained everything I was wondering about. I must confess I didn't know it was the Aswan dam that was causing these changes in the Delta. It's obvious the dam prevents the annual inundation of ancient times, but I never put two and two together. I wonder if the engineers who planned the dam saw any of this coming.

I agree with isisinacrisis that it would be fascinating to see an inundation again--the same event that provided Egypt its rich topsoils since man first found his way there. But you can imagine the kind of havoc it would wreak on the modern population and infrastructure. It will never happen again. Still, Egypt is an agrarian society.

The ancients were brilliant. They knew they had to bring the river to their crops, so they crisscrossed their floodplain with irrigation canals so their crops would flourish. Some of those ancient canals still remain. And they knew there would be lean seasons, when the inundation would be inadequate (and thus the deposit of topsoils would be inadequate), so they stored grains and crops against the possibility of famine. It didn't always work, of course. Years of steady drought are one thing that probably led to the troubles of the First Intermediate Period, and in fact, in the Fayum region, there is growing evidence from this period that cannibalism was occurring.

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Longer than the Egyptians have had writing, they have been farming the fertile land along the Nile.


No question there. The more we study hieroglyphs, the older they seem to get. We've now been able to push writing back in ancient Egypt to some 5300 years ago. But the human populations of Egypt were ancient even then. The consensus is that people first started inhabiting this Nile region some 14,000 years ago, when the deserts were lush savanna that teemed with wild animals. And all evidence suggests the earliest Egyptians began the domestication of cattle around 8,000 years ago; shortly thereafter they began to farm, as well.

Nice post, Diorite. Very informative. Thanks.
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PostPosted: Wed Jun 08, 2005 3:34 pm    Post subject: Reply with quote

There's another scary point about the dam at Aswan. In this time and age of terrorism, security at the dam is at an all-time high. Did anyone whose been there notice you can't stop on the dam at all? And taking pictures of it a big "no-no"?
Can you imagine that, if a terrorist group would plan to blw up the dam--as some have--what a tremendous wall of water would rush to the Sea? Almost all of Egypt would be wiped out!
Although the dam has brought improvements to the small villages--control of the flooding, electrical power, etc.--it has shown to have more faults than benefits.
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PostPosted: Wed Jun 08, 2005 11:37 pm    Post subject: Reply with quote

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There's another scary point about the dam at Aswan. In this time and age of terrorism, security at the dam is at an all-time high.


I'd never even considered the possibility of terrorism there. That is scary! Tells you a bit about how sick and twisted and pathetic these types are, actually considering bringing down a dam for their "cause." All it would do is wipe out the livelihood of farmers and herders and merchants up and down the Nile, devastate a great many towns and villages, and kill possibly many thousands of completely innocent people. I hope the Egyptian government keeps a close eye on that region. Very scary thought.
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PostPosted: Thu Jun 09, 2005 3:54 am    Post subject: Reply with quote

And it goes to show how smart the ancient Egyptians were and how dumb modern man is - they didn't build on the flood plain (hey, it's a plain built by flooding!). Flood came. Ho Hum. It strikes me as insane that the Egyptians are currently building on the flood plain over perfectly good farm land and turning it into urban areas.

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