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 support. Although Dulles believed that Nasser was only bluffing and that the USSR would not aid Nasser, he was wrong— the USSR promised Nasser a quantity of arms in exchange for a deferred payment of Egyptian grain and cotton. On 27 September 1955, Nasser announced an arms deal, with Czechoslovakia acting as a middleman for the Soviet support. Instead of attacking Nasser for turning to the Soviets, Dulles sought to improve relations with him. This explains the later offer of December 1955, in which the U.S. and Britain pledged $56 and $14 million respectively towards the construction of the dam.