To successfully sink a caisson, it's imperative that the flow velocity within the closing gap is minimized; thus, the operation is conducted during slack water. Given the extremely brief period during which the current is genuinely still, the sinking process must commence while the tidal flow remains at a manageable low speed. Past experiences with caisson closures have demonstrated that this speed should not exceed 0.3 m/s, guiding the timing for various phases of the operation as follows:
This schedule dictates that flow speeds must reduce to 0.30 m/s at most 13 minutes before slack water and to 0.75 m/s at most 30 minutes before. Considering the sinusoidal nature of tides in the Netherlands, with a cycle of 12.5 hours, the maximum velocity in the closing gap should not surpass 2.5 m/s. This velocity threshold can be ascertained through a storage/basin analysis. The accompanying diagram illustrates outcomes for sill heights at MSL -10 m and MSL -12 m, indicating that a sill at MSL -12 m is necessary as the sinking time at MSL -10 m is insufficient. Consequently, caisson closures are feasible only at considerable channel depths.