404 THE FUTURE OF ARID LANDS 
Figure 1. Flood water irrigation. I. Tributary wadis (Schematic). 
Il. Tributary wadis (Plane view). III. Broad flat wadis (Plane view). 
(Direction of flow is from right to left.) 
SS—Stone shelves on contour lines; BR—Bush reinforcement; CT— 
Cultivated terrace in water course; PA—Ponded area in water course; 
ED—Earth dyke on contour lines; SP—Stone spillway with reinforce- 
ment of dyke tip. 
force of the flood be harnessed so that the work done in the lower 
part of the wadi may not be totally demolished. The total length 
of the wadi is terraced by a series of broad masonry shelves into 
level plots, each lower than the preceding one—like the stairs of a 
staircase. These shelves are quite low (25-50 cm). The wadi is 
thus completely transformed into a series of terraces, narrow (a 
few meters wide) in the upper parts of the wadi and broader in 
its lower parts (Figure 2). 
The velocity of the water is thus considerably reduced, the 
