The Effect of Tailwater on the USBR Type III Stilling Basin Model

Abstract

This study evaluates the impact of tailwater on the USBR Type III stilling pond model, which is often used to construct reservoirs with low hydrostatic pressure and small flow rates. The model includes channel blocks, barrier blocks, and end barriers to dampen energy, converting flow from supercritical to subcritical. Hydraulic characteristics, including potential jump types, pressure regimes, and forces on the barrier, are not considered. Any change in discharge during the test also changes the tailwater depth position. The purpose of this study was to determine the effects of tailwater conditions on water height (y1 and y2), pool length (Lj), Froude number (Fr), critical depth (yc), and energy dissipation effectiveness (ΔE). This study shows that the average energy dissipation ratio of USBR Type III Quiet Pool is 87.45% without the effect of Tailwater, with an efficiency rate of 12.55%. When exposed to Tailwater, the average energy dissipation ratio drops to 69.47%, resulting in an efficiency rate of 30.53%. The optimum stilling pond performance is affected by the presence of tailwater (Tw), which reduces the energy dissipation ratio. The depth of the tailwater aids in the dissipation that occurs. Technical abbreviations will be explained in the first use. The water level rise under tailwater conditions exceeds that without tailwater. This finding shows tail water's importance for height rise and flow conditions. Flow conditions with Froude Number (Fr2) values of 0.22 (<1) and Tw are classified as subcritical flow.