PROBLEMS AND RESULTS IN ISRAEL 405 
percentage of percolating water is increased, and greater depth of 
water penetration is achieved (Figure 3). 
Soil particles brought by the run off water from the slopes are 
deposited on the terraces, the soil quality and topography of which 
are thus slowly improved, and the terraces further leveled. 
The stone dams can be reinforced by the planting of bushy 
plants like edible Atriplex halimus, on inedible Thymelaea hirsuta, 
etc., in front of each dam. A “‘bush-dam” alone may be sufficient 
and at times even better than a stone dam. The considerations are: 
(a) The bush-dam is pliable and may be better able to withstand 
the force of the flood than solid stone or earth dams. (4) The dam 
would grow in size concurrently with the silting processes. (c) The 
bush-dam filters the flood water, thus enriching the soil with or- 
ganic matter. (7) The costs of construction are lower. (e) Conse- 
quently, more dams may be planted per unit area. (f) The plants 
themselves may provide grazing, but as this may prove detri- 
mental for the dam, inedible species may have to be used to 
replace the edible ones. 
Main Wadis 
Floods in main wadis are very strong and cannot be completely 
stopped by any sort of dam. They can, however, be slowed down. 
Thus floods cannot be prevented but have to be brought under 
control in some other way. 
According to the quality of the beds of the main wadis, they are 
agriculturally treated in different ways. 
(a) Broad, flat beds are covered by a deep layer of loess. An 
earthen dyke is built across the wadi on the contour. The dyke 
does not, however, reach across the wadi, but terminates a few 
meters before reaching the opposite bank, and is terminated by a 
broad spillway. The next dyke downstream is built just the other 
way around with its spillway on the opposite bank. The threshold 
of the spillway is constructed several decimeters higher than the 
wadi bed. The water is thus forced to follow a much longer zigzag 
course down the wadi, instead of running straight down it, and a 
shallow pond forms behind each dyke. This artificially creates a 
much gentler slope and slows down the velocity of the water con- 
