Submerged weir formula

Excerpt from: Rajaratnam, N., Muralidhar, D., 1969. Flow below deeply submerged rectangular weirs. Journal of Hydraulic Research 7, 355–374.

In submerged flow, the flow rate depends on the upstream water level $h_{amont}$ and the downstream water level $h_{aval}$ (Rajaratnam et al., 1969):

$$Q=Cd\sqrt{2g}L{h}_{aval}\sqrt{h_{amont}-h_{aval}}$$

With:

• L the weir width in m
• h_amont the upstream head on the weir in m
• h_aval the downstream head on the weir in m
• C_d the discharge coefficient (equal to 0.9 by default).

This formula is not recommended for flooding below 80%.

Rajaratnam, N., Muralidhar, D., 1969. Flow below deeply submerged rectangular weirs. Journal of Hydraulic Research 7, 355–374.