<P> The drought that affected Sudan in the 1980s was a natural disaster that had a crushing effect on the country's irrigation systems . In 1990 - 91, for instance, water was so scarce in the Tawkar area that for the first time in 100 years the crops failed . </P> <P> As of 1990, the country's largest irrigation project had been developed on land between the Blue and White Nile rivers south of their confluence at Khartoum . This area is generally flat with a gentle slope to the north and west, permitting natural gravity irrigation, and its soils are fertile cracking clays well suited to irrigation . The project originated in 1911, when a private British enterprise, Sudan Plantations Syndicate, found cotton suited to the area and embarked on what in the 1920s became the Gezira Scheme, intended principally to furnish cotton to the British textile industry . Backed by a loan from the British government, the syndicate began a dam on the Blue Nile at Sannar in 1913 . Work was interrupted by World War I, and the dam was not completed until 1925 . The project was limited by a 1929 agreement between Sudan and Egypt that restricted the amount of water Anglo - Egyptian Sudan could use during the dry season . By 1931 the project had expanded to 450,000 hectares (1,100,000 acres), the maximum that then could be irrigated by the available water, although an additional 10,000 hectares (25,000 acres) were added in the 1950s . The project was nationalized in 1950, and was operated by the Sudan Gezira Board as a government enterprise . In 1959 a new agreement with Egypt greatly increased the allotment of water to Sudan, as did the completion in the early 1960s of the Manaqil Extension on the western side of the Gezira Scheme . By 1990 the Manaqil Extension had an irrigated area of nearly 400,000 hectares (990,000 acres) hectares, and with the 460,000 hectares (1,100,000 acres) eventually attained by the original Gezira Scheme, the combined projects accounted for half the country's total land under irrigation . </P> <P> In the early 1960s, the government set up a program to resettle Nubians displaced by Lake Nubia (called Lake Nasser in Egypt), which was formed by the construction of the Aswan High Dam in Egypt . To provide farmland for the Nubians, the government constructed the Khashm al Qirbah Dam on the Atbarah River and established the Halfa al Jadidah (New Halfa) irrigation project . Located west of Kassala, this project was originally designed to irrigate about 164,000 hectares (410,000 acres). In 1982 it was the only large irrigation project in the country that did not use the waters of the Blue Nile or White Nile . The resettlement was effected mainly after completion of the Khashm al Qirbah Dam in 1964 . Part of the irrigated area was also assigned to local inhabitants . The main commercial crops initially introduced included cotton, peanuts, and wheat . In 1965 sugarcane was added, and a sugar factory having a design capacity of 60,000 tons was built to process it . The project enabled 200,000 hectares (490,000 acres) of land to be irrigated for the first time . Heavy silting as well as serious problems of drainage and salinity occurred . As a result, by the late 1970s the reservoir had lost more than 40 percent of its original storage capacity and was unable to meet the project water requirements . These problems persisted in the early 1990s . </P> <P> The multipurpose Roseires Dam was built in 1966 and power - generating facilities were installed in 1971 . Both the water and the power were needed to implement the Rahad River irrigation project located east of the Rahad River, a tributary of the Blue Nile . The Rahad entered the Blue Nile downstream from the dam and during the dry season had an insufficient flow for irrigation purposes . Work on the initial 63,000 hectares (160,000 acres) of the project began in the early 1970s, the first irrigation water was received in 1977, and by 1981 about 80 percent of the prepared area was reported to be irrigated . (In May 1988, the World Bank agreed to provide additional funding for this and other irrigation projects). Water for the project was pumped from the Blue Nile, using electric power from the Roseires plant, and was transported by an eighty - kilometer - long canal to the Rahad River (en route underpassing the Dindar River, another Blue Nile tributary). The canal then emptied into the Rahad above a new barrage that diverted the combined flow from the two sources into the project's main irrigation canal . Irrigation was by gravity flow, but instead of flat field flooding, furrow irrigation was used, because it permitted more effective use of machinery . </P>

Why does sudan have a low percentage of arable land