Liquid reservoir

A liquid reservoir comprising

• an open-topped container having at least one side wall, a first floor fixed relative to said at least one side wall and a second floor above the first floor which is able to move upwardly and downwardly relative to said at least one side wall,
• said wall and floors being of a rigid material which is water impermeable,
• said second floor comprising a plurality of downwardly-open compartments,
• means for varying the specific gravity of the second floor between a first value less than and a second value greater than the specific gravity of the liquid in the reservoir,
• said specific gravity-varying means comprising means for supplying gas under pressure into said downwardly-open compartments, at least one trimming tank mounted on in one of said downwardly-open compartments of the second floor and means for introducing liquid from the reservoir into said at least one trimming tank and for displacing liquid from said at least one trimming tank to control the inclination of said second floor, and
• at least one passageway between first and second spaces in the container situated repectively above and below the second floor enabling liquid to flow from one end of said spaces to the other when the height of said second floor is adjusted relative to the first floor employing said specific gravity-varying means.