Without the Nile there would be no Egypt. The modern Nile has been flowing through Egypt for thousands of years, taking not only water with it, but also sediment in the form of sand, silt and clay. This sediment ensures that the delta has been created and continues to exist. But what if the sediment supply decreases?
Current issues
We already talked about the Nile in an earlier article on Kennislink. The delta as a whole is sinking because, among other things, a lot of sediment is being held back by a dam further upstream since 1964. In addition, sediment layers of the delta naturally descend because water is forced out of these layers by the pressure of the overlying sediment.
If that were the only problem, it might have been manageable, but the delta sediments also contain a lot of organic material, which oxidizes slowly. As a result, the delta is also slowly declining, not to mention the extraction of oil and gas in the area. There are therefore plenty of problems with the rising sea level, also in the Mediterranean Sea.
News
According to Nick Marriner and colleagues at the French Centre national de la recherche scientifique (CNRS) too little sediment has been coming to the delta for 4000 years. His team examined sediments from 194 points on the vast Nile Delta, which is now home to 50 million people and 60% of Egypt's food. Between 8000-4000 years ago, much more sediment was transported to the delta by the Nile. The naturally collapsing delta (0.03 to 4.5 mm/yr depending on the location on the delta) kept its head above water very well:more sediment was added than the delta fell.
That changed drastically around 4000 years ago. An astronomically-driven change in the climate is partly to blame for this:the intertropical convergence zone moved south. “The ITCZ is a moss-rain tyre,” lead author Marriner tells Kennislink. “Because the ITCZ is shorter above the Ethiopian Highlands [where part of the Nile water comes from, ed.] compared to the Early Holocene, less sediment is produced. The more northern Early Holocene ITCZ, on the other hand, provided the well-known Green Sahara.”
The second reason is that the ancient Egyptians started using part of the Nile water for irrigation purposes. Humans thus exacerbated the situation of sediment shortage early in history.
Soil subsidence
The sediment shortage can now be seen in subsidence that is no longer canceled out by the sediment supply. The subsidence of the soil layers is greatest in the lagoons near the coast, in contrast to further inland where the soil hardly sinks. “The youngest sediments are deposited around the mouths of the current river,” Marriner says. “Studies show that sediment loses volume most rapidly in the decades and centuries immediately after deposition.”
Moreover, many lagoons lie on top of old river valleys from the Pleistocene, the period before the Holocene in which many glacials occurred and rivers cut deep into the landscape. “This highly incised landscape was filled with sediment in the Holocene.” A thick layer of relatively young sediment compared to other areas therefore collapses easily.
Lock
Two important conclusions. Marriner:“The Nile Delta has a fairly long history of vulnerability due to climate-driven changes in the [natural] supply of sediment and human influence.” With relatively recent developments such as sea level rise and the extraction of fossil fuels, the existence of the Nile Delta (and therefore the habitat of millions of people) is increasingly threatened.
- Nile Delta:to sink or to drown? (background)
- Mississippi delta drowns (news)
- Influence of sun and Nile on Mediterranean climate (background KNMI)
- Evolution catch in source of Nile (background Bionieuws)
- The catastrophic Mediterranean flood (news)
- Weir dams mask sea level rise (news)