Investigation of the head loss of ogee spillway and the length of hydraulic jump due to the confliction of the stream lines over the body of ogee spillway

Constructing stilling basins usually are expensive، so reduction of stilling dasins length is economically important. The dimensions of the stilling basin depend on the length and sequent depth of hydraulic jump. Therefore، increasing the energy loss in dam structure decreases the length and sequent depth of hydraulic jump and as a result reduces the stilling basin cost. Also in designing of diversion dam، in order to prevent the agricultural land flooding during the flood season، a smaller height of diversion dam is designed and this may produce many difficulties for upstream intake structures. In this research study a combination of two jets in ogee dam was used، in order to increase the energy loss along the dam structure and to reduce the hydraulic jump length and sequent depth. The laboratory models of ogee dams were designed and built based on the USBR standards with a designed slot near to the toe of the dam. In these experiments the directions of the flow out of the slot were 0، 45 and 90 degrees in respect to the horizontal line. The effect of six discharge ratios (discharge from the slot to the total discharge) for each angle was investigated on the hydraulic jump length and sequent depth. The Froude Number was measured 1. 5 to 4. 5. The results showed that the angle 45 degrees has the maximum effect on reducing the hydraulic jump length and sequent depth، with an average discharge ratio of 26% the hydraulic jump length being reduced about 50% in comparison with the classic jump. This structure is also able to increase the total discharge coefficient.