Experimental investigation of hydraulic parameters in modern horseshoe spillway

Modern horseshoe spillways are combination of external and internal weirs and determination of hydraulic parameters of this kind of spillways is essential. In this study, by making physical models of Modern horseshoe spillway in laboratory dimension, some hydraulic parameters of modern horseshoe spillways like discharge coefficient, discharge rate through the two weirs and water surface profiles in different parts of horseshoe weir are investigated. The results showed that by increasing the ratio of head (h) to external weir’s Length (Lw) for Lw≤100 cm, the discharge coefficient for internal weir (CO) increases linearly. By increasing ratio of internal weir discharge to external weir discharge Q1/Q2, the discharge coefficient has a decreasing trend between 0.65 to 0.3 . By increasing the external weir length, the discharge rate through external weir increases while it decreases in internal weir. The external weir with Lw=100 cm has better performance than other Lws and If we select it as the better length, on average 31 percent of the flow will pass from the internal weir. Classic and Modern horseshoe spillways are able to reduce the head above the weir respectively to 28 and 50% in comparison to rectangular weir head with the same width. Investigation of the water surface profiles shows that by creating an internal weir, rooster tail hydraulic jump that existed in Classic horseshoe spillway is removed.