365 Days of Climate Awareness 244 — The Nile River
The Nile is the longest river in Africa, and possibly (estimates vary versus the Amazon) the longest river on earth, measuring 6,650 km/4,130 mi.
The Nile is the longest river in Africa, and possibly (estimates vary versus the Amazon) the longest river on earth, measuring 6,650 km/4,130 mi. It has two major tributaries: the White Nile, which originates in Lake Victoria in the Great Lakes Region of Kenya, Tanzania and Uganda. However, about 80% of the water and silt of the lower Nile come from the shorter Blue Nile, which originates in Lake Tana in Ethiopia. Though Lake Tana is significantly smaller than Victoria, and the Blue Nile’s drainage basin is similarly smaller than the White Nile’s, precipitation and erosion are much higher in that area of Ethiopia than in the Great Lakes region. The two tributaries meet at Khartoum in Sudan, where it flows northward through the desert toward its delta on the Mediterranean.
The Nile has flowed for more than 25 million years. For much of that time the Mediterranean Sea was much lower than it is now, and the river reached it via a massive ravine dug into the African bedrock. The ravine still exists, but is now backfilled with sand and silt, following the Messinian Salt Crisis 5–6 million years ago. That is the name for the event when the ridge connecting Spain to Africa broke, and the Atlantic Ocean came spilling into the previously mostly dry Mediterranean. Hypotheses vary on the duration of this flood, whether catastrophic (1–3 years), or gradual (>10K years), but they center on a date of 5.3 MYA. And in each case, the mighty Nile canyon was filled with sediment as sea level rose toward the surrounding continents.
The Aswan High Dam, completed in the late 1960’s, provides Egypt with flood control and hydroelectricity. It was designed by Moscow’s Hydroproject Institute, and is the largest embankment dam on earth: it is made not of concrete but mounded and compacted earth. It provides about 2.1 GW of electricity. The dam has presented Egypt and Sudan with a number of technical challenges. Primary among these is the deposition of sediment above the dam — the Nile’s annual load is roughly 230 x106 tons/year —…
