406 THE FUTURE OF ARID LANDS 
Figure 2. Flood water irrigation in tributary wadis in the Negev 
Highlands. Two tributaries, completely terraced up to the watershed, 
stone shelves reinforced with inedible bushes (Thymelaea hirsuta, 
Haloxylon articulatum, etc.). 
siderably. Danger of erosion is thus reduced, and at the same time, 
the water has more time to percolate and moisten deeper layers of 
the ground. The design of these structures is planned on topo- 
graphic maps (Figure 1, III). 
(6) Broad loess wadis are longitudinally dissected by a steep 
stony watercourse. In this case the shape of the watercourse pre- 
vents any flood control. However, it may be, and has been in an- 
cient times, utilized by diversion and spreading on the loess banks, 
and on higher lying fields on the slopes. That the Nabataeans and 
Byzantines were masters in this type of agriculture is proved by 
the very extensive system of terraces left by them and by the 
excellent, solid quality of the stone walls built round the terraced 
fields. These fields, which accompany the wadi bed on both sides 
along its course, are leveled and their edges are protected by low 
stone walls. The main terrace wall runs perpendicular to the course 
