Aswan extremity of Egypt, the river flows for more than without bar or cataract. The voyage from Aswan to Alexandria usually took 21 to 28 days in favourable weather. Aswan has a hot desert climate (Köppen climate classification "BWh") like the rest of Egypt. Aswan and Luxor have the hottest summer days of any city in Egypt. Aswan is one of the hottest, sunniest and driest cities in the world. Average high temperatures are consistently above during summer (June, July, August and also September) while average low temperatures remain above . Summers are long, prolonged and extremely hot. Average high temperatures
Hydropower policy in the United States of 90% efficiency. More importantly, Francis's mathematical and graphical calculation methods advanced turbine design and engineering and allowed confident design of high efficiency turbines to exactly match a site's flow conditions. In the 1870s and deriving from uses in the mining industry, the high efficiency Pelton wheel impulse turbine was developed to use hydropower under very different flow and pressure conditions. Advances in dam design also progressed, with the completion of Old Aswan Dam being considered a milestone of engineering over nature. At the time of its construction, nothing of such scale had ever been attempted: it also became one