124 



FORESTRY AND IRRIGATION 



March 



Except for those small areas of land 

 lying too high to be reached by the or- 

 dinary floods of the Nile, the ancients 

 used only the basin system of irrigation. 

 This method consists of flooding the 

 land to a depth of from 3 to 5 feet at 

 the season of high Nile and of main- 

 taining this depth of water for about 

 six weeks, when the water is drained 

 back into the Nile and the seed is sown, 

 without plowing or other cultivation, 

 on the surface of the newly deposited 

 mud. In this way but one crop could 



the capillary forces were unable to re- 

 turn them to the surface before the 

 next annual flood. Upon the aban- 

 donment of this method, however, the 

 movement of soil moisture was entirely 

 from below, and the soluble salts grad- 

 ually accumulated at the surface. 



The first step toward reclamation is 

 the construction of canals for irrigation 

 and of ditches for underdrainage. Irri- 

 gation water is taken by a large canal, 

 which subdivides and ramifies over the 

 entire area to be irrigated. The drain- 



ABUKIR TRACT, WHICH IS BEING RECLAIMED FROM SALT. 



be grown each year. The higher lands 

 were covered only by the highest floods, 

 or only eight or nine times in a century. 

 During the remaining years these lands 

 were irrigated by lifting the water from 

 the canals or the river. It can readily 

 be seen that there was little opportunity 

 for the accumulation of alkali salts so 

 long as the basin method of irrigation 

 was kept up, for the large amount of 

 water which washed over and through 

 the soil each year either removed the 

 salts or washed them down so deep that 



age water is drawn off and discharged 

 into a lake or the Mediterranean. 



The accompanying plans show two 

 methods of placing the canals and 

 drains, both of which are in general 

 use. 



By the first plan (Fig. i) the second- 

 ary drains run half way between the 

 secondary canals, and into them the 

 tertiary drains or laterals run from each 

 side. These tertiary ditches are 150 

 meters (492 feet) long, 80 centimeters 

 ^2 inches) deep, 25 centimeters (9.8 



