And in Omar's time the _Sawâd_ was no longer at its best, for, a few years before the Arab conquest, abnormally high floods had burst the dykes; from below Hilla to above Basra the Euphrates broadened into a swamp, and the Tigris deserted its former (and present) bed for the Shatt-el-Hai, leaving the Amara district a desert. The Persian Government, locked in a suicidal struggle with Rome, was powerless to make good the damage, and the shock of the Arab invasion made it irreparable[58]. Under the Abbasid Caliphs of Bagdad the rest of the country preserved its prosperity, but in the thirteenth century Hulaku the Mongol finished the work of the floods, and under Ottoman dominion the _Sawâd_ has not recovered. Can it still be reclaimed? Surveys have been taken by Sir William Willcocks, as Adviser to the Ottoman Ministry of Public Works, and his final conclusions and proposals are embodied in a report drawn up at Bagdad in 1911[59]. "The Tigris-Euphrates delta," he writes, "may be classed as an arid region of some 5,000,000 hectares.... All this land is capable of easy levelling and reclamation. The presence of 15 per cent. lime in the soil renders reclamation very easy compared with similar work in the dense clays of Egypt. One is never far away from the giant banks of old canals and the ruins of ancient towns." But he does not expect to make all these 5,000,000 hectares productive simultaneously, as they are said to have been when Omar took his inventory. "It is water, not land, which measures production," and he reckons that the average combined discharge of the rivers would irrigate 3,000,000 hectares in winter, and in summer 400,000 of rice or 1,250,000 of other crops. This is the eventual maximum; for immediate reclamation he takes 1,410,000 hectares in hand. His project is practically to restore, with technical improvements, the ancient system of canals and drains, using the Euphrates water to irrigate everything west of the Tigris (down to Kut) and the Shatt-el-Hai, and the water of the Tigris and its tributaries for districts east of that line. Adding 33 per cent. for contingencies to his estimate for cost of materials and rates of labour, and doubling the total to cover interest on loans and subsequent development, he arrives at £29,105,020 (Turkish)[60] as the cost, from first to last, of irrigation and agricultural works together; and he estimates that the 1,410,000 hectares reclaimed by this outlay will produce crops to the value of £9,070,000 (Turkish) a year. In other words, the annual return on the gross expenditure will be more than 31 per cent., and under the present tithe system £7,256,000 (Turkish) of this will remain with the owners of the soil, while £1,814,000 will pass to the Government. This will give the country itself a net return of 24.9 per cent. on the combined gross cost of irrigation and agricultural works, while the Government, after paying away £443,000 (Turkish) out of