Ancient Egypt Day 6

We saw many mirages as we crossed the desert. I was fascinated to note that the mirages are sometimes inverted, as in the top mirage here, and sometimes not, as in the lower one. Explanations on a postcard, please...

One problem is the waste of water - about 10 billion m3 of water evaporates from the lake each year. Another major problem is that silt accumulates in the lake instead of being carried further downstream. The absence of silt in the water further north means that farmers have to use chemical fertilizers. The erosion of the delta region is no longer compensated by the arrival of silt, and the reduced flow of the river is not enough to stop salt water encroaching into the delta, where up to 40% of the earth has been sterilized by the salt. A project to create a 'second Nile valley' parallel to the first is progressing slower than predicted and may not compensate the problems mentioned above. But the existence of the lake did at least protect Egypt from years of drought which caused thousands of deaths in the Sudan a few years ago.