Sluice Gate

Figure 120: Sluice gate geometry

The sluice gate is the upstream element of a channel and is illustrated in Figure 120. The element downstream of a sluice gate should be a straight channel element. The interesting point is that the gate height $h_g$ may be part of the backwater curve, but it does not have to. If the lower point of the gate is higher than the fluid surface, it will not be part of the backwater curve.

If the gate door touches the water and the water curve is a frontwater curve (curve A in Figure 120) the volumetric flow $Q$ is given by (assuming $\theta=0$)

$$Q=b h_g \sqrt{2 g (h-h_g \sqrt{1 - S_0^2})},$$ (174)

if the gate door does not touch the water and the water curve is a frontwater curve the volumetric flow $Q$ is given by

$$Q=b h_c \sqrt{2 g (h-h_c \sqrt{1 - S_0^2})},$$ (175)

where $h_c$ is the critical depth. The critical depth is the value of $h_c$ in the above equation for which $Q$ is maximal. For a rectangular cross secton $h_c=2h/3$. If the gate door touches the water and the water curve is a backwater curve (governed by downstream boundary conditions, curve B in Figure 120)) the volumetric flow is given by

$$Q=b h_g \sqrt{2 g (h-h_d \sqrt{1 - S_0^2})}.$$ (176)

Finally, if the gate door does not touch the water and the water curve is a backwater curve the volumetric flow is given by

$$Q=b h_d \sqrt{2 g (h-h_d \sqrt{1 - S_0^2})}.$$ (177)

The following constants have to be specified on the line beneath the *FLUID SECTION,TYPE=CHANNEL SLUICE GATE card (the width, the trapezoid angle, the slope and the grain diameter should be the same as for the downstream element immediately next to the sluice gate; they are needed for the calculation of the critical height and normal height):

• the width $b$
• the trapezoid angle $\theta$
• not used
• the slope $S_0 = \sin \phi, -1<S_0<1$ (for this element the slope must be given explicitly and is not calculated from the coordinates of the end nodes belonging to the element)
• the grain diameter $k_s$ for the White-Colebrook law or the Manning constant $n$ for the Manning law (in the latter case the user has to specify the parameter MANNING on the *FLUID SECTION card)
• the height of the gate door $h_g$

Example files: channel1, chanson1.