Splash zone applies either to the Supralittoral zone or, in the context of Offshore construction, to the transition from air to water when lowering heavy burdens into the sea. The overall efforts applied on the crane change dramatically when the load starts touching water, up to the point where it is completely submerged. Its buoyancy reduces the static mass that the crane has to support, but contact with the waves creates widely fluctuating dynamic forces.
Simulation of these changing efforts are necessary to correctly dimension cranes and lifting equipments. See for example DNV-RP-H103 (Det Norske Veritas recommended practices) for a mention of the piston effect created in the splash zone between two walls.