The boundary equations of different flow cases for compound hydraulic structure have been found in this paper. A weir was fixed under sluice gate in a rectangular flume form a jet of water from the opening between the two structures.
The tail water elevation has been changed gradually from the edge of weir to (25cm) depth from the channel bed. Through the experimental program four flow cases have been formed(A,B,C&D).Case(A) happened when tail water depth (10cm) or less (case of free jet), Case (B) happened when tail water depth greater than (10cm) till the edge of the sluice gate, Case (C) happened only when the gate opening was (1cm) and the tail water depth was between(14-15)cm (case of oscillating jet), this case causes severe vibration and must be avoided in design. Finally, case (D) happened when tail water above edge of the gate (case of submerged jet).