The document discusses water pressure on lock gates used to transfer boats between different water levels on opposite sides of dams. It describes how lock gates work and how water pressure creates forces on the gates. Specifically, it explains that water pressure creates a force P on each gate, and the gates exert an equal and opposite reaction force F on each other. The total pressure is shared between the top and bottom hinges of each gate. Mathematical equations are provided to calculate the individual reaction forces on the top and bottom hinges based on the water levels, gate dimensions, and other parameters. As an example, calculations are shown to determine the force acting on each gate for a given lock gate configuration and water levels.