mahboobeh shahabi - m.sc student civil engineering department of shiraz university
nasser talebbeydokhti - professor shiraz university
ahmad dehghani amir - assistant professor gorganuniversity
abnoulrasoul telvari - assoc prof islamic azad university ahvaz

Weirs and gates are the common and important structures which are used in controlling and adjusting the flow in irrigation channel. One disadvantage of the sluice gates is the possibilities of retaining the floating materials which can be resolved if they combined with the weirs. Also sedimentation problem in weir can be resolved by combination of weirs with sluice gates. These combined structures have a new hydraulic condition that is different with weir condition solely or we have only gate. This paper presents the result of an experimental study on the characteristics of scour hole resulted by contracting the weir and gate cross section. The results showed that by contraction, the ratio of hs/(w+a) (hs is maximum scour, w is the vertical distance between the gate top and the weir bottom and a is the gate opening) increase and the length of scouring and sedimentation decrease. And with increasing the gate opening the maximum scour decreases. The results also show that the maximum depth of scour in combined flow structure is less than weir or gate.

Scour, Combined flow, Weir, Gate, Contraction