During the flow of water in closed drains at high speeds, the pressure can drop to the value that causes the phenomenon of cold boiling and the subsequent formation of dangerous cavitational pockets. High speeds also lead to the attraction of the surrounding air and thus the occurrence of the phenomenon of spontaneous ventilation, which plays an opposite role to the phenomenon of cavitation within the structure of the stream, and a role Negatively in the creation of cavernous pockets above the surface of the water.