Abstract: A method of forming a trench in the bed of a body of water, the bed having an initial undisturbed upper surface, comprises suspending a pressure line from a vessel floating on the body of water, the pressure line terminating downwardly in a downwardly directed nozzle. The nozzle is positioned a small distance above the bed, and water is pumped under pressure on board the vessel and is discharged via the pressure line and nozzle downwardly against the bed surface with the water pumped at an overpressure between 0.01 bar and 20 bar and at a flow rate of 0.25 to 20.0 cm per second. The distance of the nozzle above the surface of the bed is not more than ten times the diameter of the water jet defined by the nozzle, preferably about six times the diameter of that water jet.

Abstract: In a method for treating the bed of a body of water by means of a directed water jet, which water jet is moved over the bed (5) in accordance with an elongated path, the water is pumped under pressure on board a vessel (1) and then discharged, via a pressure line (2) connected to said vessel (1), a small distance above, and directed towards the bed (5). With this procedure, a trench (6) can be formed in the bed.

Abstract: A device for creating a localized water jet within a body of water allows for the displacement of material from the floor of the body of water. The device includes two powered screws within a jet pipe. The screws are arranged coaxially and their direction of rotation, pitch, and speed of rotation are arranged such that the torque produced by one of the screws tends to counteract the torque produced by the other, allowing for improved control of the device.