The level of the Nile at Wâstah at the end of April may be taken to be 18·75 The distance from Wâstah to Lahûn is 30 kilometres. „ Lahûn to Hawârah 15 „ -- Total 45 „ Allowing a water surface slope for the outflow of ¹⁄₂₅₀₀₀, the difference in water surface level between the lake at Hawârah and the Nile at Wâstah would be 1·80 ----- Hence the water surface of the lake at the end of April would be at 20·55 Evaporation would still further lower the surface in May by ·25 „ „ „ June „ ·30 --- 0·55 ----- The water surface in the lake would thus become 20·00 Probably the commencement of the flow into the lake would not take place till a few days after the middle of July, which may be taken as the time when the lake reaches its lowest level for the year. Evaporation for this period of July must therefore also be allowed for, say 0·20 ----- The lowest level of the lake would therefore be 19·80 The mean surface area of the Lake Fayûm between R.L. 19·80 and 25·00 may be taken as 2000 million square metres. Evaporation during the ninety days of flood would tend to lower the level 70 centimetres. The quantity of water required to raise the lake from R.L. 19·80 to 25·00 would therefore be 2,000,000,000 × (5·20 + 0·70) = 11,800 million cubic metres, or a daily average for ninety days of 131,111,111 cubic metres. At the commencement of these ninety days the inflow would be small, increasing rapidly to the maximum; and again, as the lake level rose and the Nile began to fall in October, the inflow would gradually decrease to nothing by the end of the ninety days. Hence it would probably be necessary to suppose a maximum daily discharge into the lake of about 200 million cubic metres a day for part of the time.