Aswan Dam assumption did not take into account the extent of perennial irrigation that was already present throughout Egypt decades before the high dam closure. By the 1950s only a small proportion of Upper Egypt had not been converted from basin (low transmission) to perennial (high transmission) irrigation. Expansion of perennial irrigation systems in Egypt did not depend on the high dam. In fact, within 15 years of the high dam closure there was solid evidence that biharzia was declining in Upper Egypt. S. haematobium has since disappeared altogether. Suggested reasons for this include improvements in irrigation practice. In the Nile Delta,
Aswan the summer solstice, a vertical staff cast no shadow. They noted that the sun's disc was reflected in a well at noon. This statement is only approximately correct; at the summer solstice, the shadow was only of the staff, and so could scarcely be discerned, and the northern limb of the Sun's disc would be nearly vertical. However, Eratosthenes used this information together with measurements of the shadow length on the solstice at Alexandria to perform the first known calculation of the circumference of the Earth. The Nile is nearly wide above Aswan. From this frontier town to the northern