Loose stone check dams = بندهای سنگ ریزه ای
Loose stone check dams made of relatively small rocks are placed across the gully (Fig. 16). The main objectives for these dams are to control channel erosion along the gully bed, and to stop waterfall erosion by stabilizing gully heads.
Loose stone check dams are used to stabilize the incipient and small gullies and the branch gullies of a continuous gully or gully network. The length of the gully channel is not more than 100 m and the gully catchment area is two ha or less (Table 2). These dams can be used in all regions.
The maximum effective height of the dam is 1.0 m and its foundation depth is at least 0.5 m. The thickness of the dam at spillway level is 0.5 to 0.7 m and the inclination of its downstream face is 20 percent (1•1/5 ratio); the thickness of the base is computed accordingly. • The upstream face of the dam is generally vertical.
Other specifications for loose stone check dams
-The foundation of the dam is dug so that the length of the foundation will be more than the length of the spillway. The foundation of the wings should be dug in such a manner that the wings will enter at least 50 cm into each side of the gully.
-The crest and middle part must be constructed with bigger rocks than the rest of the dam.
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-The wings of the dam should be protected against flash water by wing walls. The angle between the wing wall and the wing is 30 to 45 degrees. The wing wall's height must be equal to the depth of the spillway. Fill the space behind the wing walls with soil.
-The space behind the dam should also be filled to spillway level with soil excavated for the foundation, and from the gully bed.
-The form of the spillway is concave.