Free flow sluice gate

Free flow sluice gate diagram

Excerpt from Baume, J.-P., Belaud, G., Vion, P.-Y., 2013. Hydraulique pour le génie rural, Formations de Master, Mastère Spécialisé, Ingénieur agronome. UMR G-EAU, Irstea, SupAgro Montpellier.

$W$ is the gate opening, $h_{a m}$ the upstream water level and $L$ the date width. The stage-discharge equation of the free flow sluice gate is derived from Bernoulli's load conservation relationship between the upstream side of the valve and the contracted section.

The height $h_{2}$ corresponds to the contracted section and is equal to $C_{c} W$ where $C_{c}$ is the contraction coefficient. The stage-discharge equation is often expressed as a function of a flow coefficient $C_{d}$ in the form of:

$Q = C_{d} L W \sqrt{2 g} \sqrt{h_{a m}}$

So we have the relationship between $C_{d}$ and $C_{c}$ :

$C_{d} = \frac{C_{c}}{\sqrt{1 + C_{c} W / h_{a m}}}$

Numerous experiments were conducted to evaluate $C_{d}$ , which varies little around 0.6. As a first approximation, for a low $W / h_{a m}$ (undershot gate, most frequent case), $C_{d}$ is close to $C_{c}$ and can be chosen equal to 0.6.

Discharge coefficients $C_{d}$ are given by abacuses, which can be found in specialized books if necessary. They range from 0.5 to 0.6 for a vertical sluice gate, from 0.6 to 0.7 for a radial gate, up to 0.8 for an inclined sluice gate.