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 Dam exchange rate in 1970 of $2.30 per E£1): £140 million from agricultural production, £100 million from hydroelectric generation, £10 million from flood protection, and £5 million from improved navigation. At the time of its construction, total cost, including unspecified "subsidiary projects" and the extension of electric power lines, amounted to £450 million. Not taking into account the negative environmental and social effects of the dam, its costs are thus estimated to have been recovered within only two years. One observer notes: "The impacts of the Aswan High Dam (...) have been overwhelmingly positive. Although the Dam has contributed to some