38 TUNISIA 



But any system of dams has proved unsuccessful unless the 

 supply of water has been greatly diminished by cutting off the 

 flood water supply. This is accomplished by building contour 

 ditches heading up to the edges of the ravines. 



At El-Hamma both the Roads Department and the Forest 

 Service have protected slopes from erosion, but by different 

 methods. The work of the former has not been successful. 

 The methods of the roads department has been to cover a slope 

 with diamond-shaped cordons of brush tied to anchor stakes 

 (see Fig. 8). The brush is spaced 1.2 by 2.1 metres (4 by 7 

 feet) and o.i to 0.15 metres (4 to 6 inches) high with stakes every 



FIG. 8. Method of protection against erosion at El-Hamma. 



0.35 metres (14 inches). This protective cover does not prevent 

 erosion, since the water flows underneath the brush and soon 

 cuts out a small ravine. On an even more difficult 45 slope 

 the local ranger has tried another plan which merits success. 

 The project is designed to protect an important spring used for 

 uati ring camel caravans, as well as for irrigation. This scheme, 

 which is shown in Fig. 9, consists of a series of parallel artificial 

 hedges built on contour 3 to 4 metres (3 to 4 yards) apart. 

 The hedge is of tamerisk, 40 cm. (16 inches) above the ground, 



