Dredging method and device

Abstract

A dredging method that includes suspending a dredging apparatus 200 from a vehicle 360. The sediment agitator apparatus includes a chassis 210, mounted on the chassis of an extractor, a sediment agitator, and associated pumps 220, 230. The dredging apparatus 200 is positioned above, but not in contact with, a waterbed 340 from which sediment 350 is to be dredged. The sediment 350 is agitated and then extracted by the extractor. The dredging device 200 moves around the water and the extracted sediment 400 settles below the water and above the dredging device 200, such that the sediment 400 is transported and settled away from the area being dredged by the natural movement of the water. The device and use of the device are also described.

Description

Dredging method and device

[0001] This invention relates to a method for dredging, a dredging device, and the use of a dredging device.

[0002] Dredging is generally defined as the underwater removal of sediment and its transport from one location to another. Dredging is a process that may include the steps of bringing sediment from the water surface and optionally the steps of transporting the sediment away from the dredging area and then ultimately disposing of the sediment. Optionally, the sediment may have been loosened in the first place.

[0003] Dredging can be carried out for a variety of reasons, for example, to clear a harbor or waterway where sediment has accumulated that could potentially impede shipping. Since harbors are generally deeper than the surrounding water, sediment can accumulate in the natural flow of water, for example, by tidal waters or the flow of a river, and not be removed.

[0004] Examples of prior art methods of dredging include a surface-mounted shovel or bucket that can be used to physically lift sediment into a bucket, whereby the sediment is placed in a hopper for subsequent disposal. Another prior art method of dredging is the use of trailing suction hopper dredges, which involve a vessel attached to a series of dredges in which sediment is pumped from the waterbed through the head of the hopper into a hopper on the vessel.

[0005] Prior art dredging methods involve the use of water jets that inject water into the sediment to loosen it and reduce its density, causing it to float above the water table in a so-called "density cloud." The suspended sediment is then washed away by gravity. This method is particularly useful in rivers and tidal areas where the resulting sediment density cloud can flow under gravity to deeper areas.

[0006] Another method of dredging is the use of cutter suction dredges, which consist of a rotating cutter head mounted in front of the suction head, where the cutter head rotates along the axis of the suction pipe. The cut sediment is then sucked in by a suction pump. Such cutter suction dredges are intended for use in a fixed position - even if they are mounted on a ship, the ship is anchored during use with spuds or anchor legs.

[0007] Another prior art method used to deal with the problem of sedimentation in a shipping channel or harbor is seabed leveling, whereby a plow is towed behind a vehicle to smooth out raised areas of sediment without actually removing any of the sediment from the waterbed.

[0008] Various attempts have also been made to provide dredgers that operate on the bottom of the waterbed and disrupt the sediment with cutters or high-pressure fluid jets. These devices may be self-propelled vehicles (such as those described in GB 2543764 A) or may be towed along the waterbed by a vehicle, such as those described in US2014 / 0238924 A1. Waterbed-operating vehicles create an insulating layer between the bottom surface of the dredger and the waterbed and use negative pressure to pull and remove sediment.

[0009] Other prior art dredges operate above the waterbed. For example, US 4,127,950 describes a suction head that draws sediment mixed with liquid into a vertical chamber, after which separate gas jets expel the sediment from the chamber. These dredges are cumbersome and slow to operate due to the closed, essentially solid chamber that creates a lot of drag. Such dredges also require compressed fluid to pump the gas and liquid injector from a surface reservoir.

[0010] There are several problems associated with prior art dredging methods. For example, water injection dredging requires water to flow by gravity to remove suspended sediment, so it is of little use in a coastal harbor that does not have a slope. Leveling the bed does not remove any of the sediment, it only smooths it out, and sediment can continue to accumulate over time. Trailing suction hopper dredges, while often effective in removing sediment, require expensive, custom-built equipment, including a large hopper-type vessel. Such equipment is not only expensive to acquire, but also expensive to operate. Dredging with a grab and / or backhoe is also expensive because it requires the use of a special hopper-type vessel to remove the dredged sediment.

[0011] Dredges that are placed on the waterbed are problematic in that, for example, the waterbed of a harbor is rarely flat and will contain a lot of solid debris, which makes such a dredge impractical and easily damaged. Debris that is often encountered on the waterbed of a harbor includes container attachments, which include long metal beams that fall from the container during loading and unloading. Container attachments can cause significant damage to the dredge, and significant time is then spent repairing the dredge before it can be used again, which is very expensive.

[0012] The present invention addresses the problems associated with the prior art by providing devices and methods that are not only efficient in removing sediment from a wide range of aquatic environments, but are also relatively inexpensive to operate.

[0013] According to the present invention, a method for dredging is provided, comprising: suspending a dredging device from a vehicle, the dredging device comprising: a chassis; a sediment agitator for disposing above a layer of sediment on a waterbed, the sediment agitator comprising a fluid injector and a pump positioned to inject fluid through the fluid injector, the sediment agitator and pump mounted on the chassis; an extractor, the apparatus being arranged to remove agitated sediment from the waterbed and above the dredging device, the extractor comprising a conduit and a pump arranged to pump agitated sediment through the conduit, the extractor and pump mounted on the chassis; and an interface for connecting the sediment dredging device to the vehicle; positioning the dredging device above, but not in contact with, the waterbed to be dredged of sediment; agitating the sediment with the sediment agitator; extracting the sediment with the extractor; The extracted sediment is placed underwater and above the sediment agitator, and the dredging device moves around the water; where the sediment is removed from the area being dredged by the natural movement of the water.It is transported and deposited.

[0014] The method according to the present invention operates by raising the agitated sediment to a higher water column, whereby the natural movement of the water is able to wash away the suspended sediment. In a harbor, this may mean raising the sediment to a level above the seabed outside the harbor, so that the tidal waters can wash away the sediment.

[0015] By placing the dredging device above the waterbed, dredging can reduce the problems associated with many previous devices by avoiding much debris and traversing uneven waterbeds.

[0016] The extracted sediment may be light and loose, in which case the action of the extractor alone may be sufficient to pull the sediment into the dredge and extract it, without the need to engage the sediment agitator. However, if the sediment is heavy, dense, or unagitable, the sediment agitator may be engaged.

[0017] The sediment dredging apparatus may employ a range of different sediment agitation means in addition to the fluid injector. The fluid injector further comprises a pump wherein the pump injects fluid through the fluid injector into the sediment to loosen the sediment prior to extraction. The fluid injector and pump are mounted on a chassis. The fluid injector may be located at the bottom of the sediment agitator. In particular, the injector may have an outlet which, when in use, discharges fluid in a downward direction into the sediment deposited in the waterbed. More than one fluid injector and a plurality of fluid injectors may be provided. The fluid injector may comprise one or more conduits, the conduit having a plurality of outlets or nozzles. The outlets may be spaced evenly along the conduit. A plurality of conduits may be provided in parallel along the width of the chassis. One or more conduits may span the entire width of the chassis. Multiple pumps may be provided, with one pump supplier per fluid injector or with multiple fluid injectors.The injected fluid may be water or air or a combination thereof. If the fluid is water, the fluid injector preferably comprises more than one inlet and the water is drawn in from the water surrounding the dredging device. Alternatively, the fluid may be supplied to the dredging device from the surface or from a vehicle.

[0018] Prior art dredgers that pump fluid to agitate sediment typically use high pressure jets. High pressure is defined in the art as 800-1000kPa (8-10 bar). In contrast, the fluid injected by dredgers in the present application is injected at low pressure (150-200 kPa / 1.5 to 2 bar) or medium pressure (400-500 kPa / 4-5 bar). Low to medium pressure is advantageous over high pressure jets because it requires fewer resources in terms of pump pressure and power usage and is effective in agitating sufficient amounts of sediment.

[0019] The dredging apparatus includes a chassis that supports the sediment agitator and extractor. The dredging apparatus operates above and apart from the waterbed in use, however the chassis may be suitably designed to withstand contact with the waterbed. This may occur when the dredging apparatus is lowered into place, if the waterbed is uneven, or if the vehicle is a boat and the water on which the boat is floating is choppy.

[0020] The chassis may include impact protection means to protect the dredger from impacts with the waterbed and / or debris that may be encountered during use. For example, the chassis may include buffers mounted on the underside of the chassis, or may include heavy runners to protect the underside of the chassis.

[0021] The chassis may have a generally flat, solid base, or may be in the form of an open frame, preferably with an open base. The frame may be formed of metal or plastic tubing or the like. The chassis may have side walls, an upper surface on which items such as the extraction device and sediment agitator are placed. The front and rear of the frame may be "open" allowing heavy material and debris that would otherwise damage the dredger to pass through the dredger. Additionally, having an open frame reduces drag on the chassis as it moves through the water, thereby allowing dredging operations to be carried out at a faster rate than previous dredgers.

[0022] The chassis includes opposed side panels and one or more body panels positioned parallel between the side panels and connected by one or more cross members.

[0023] One or more cross members may include a sediment agitator, and where the sediment agitator includes one or more conduits including one or more outlets for injecting fluid, the sediment agitator is in communication with one or more pumps, a pump in communication with an inlet and wherein fluid is drawn in from the surrounding area through the inlet.

[0024] Additionally or alternatively, one or more cross members may include an extractor, wherein the extractor includes one or more inlet ducts into which agitated sediment is drawn for removal, and the extractor is in communication with one or more pumps, the pump being in communication with a duct extending from the top of the dredging device to remove agitated sediment from the top of the dredging device being used.

[0025] One or more cross members may also include a rigid retaining rod. This rod may include a tapered leading edge, thus cutting any deposits encountered during use.

[0026] The chassis may include runners attached to the underside of the body and / or side panels. A leading edge of the body and side panels may be rounded to deflect debris.

[0027] The dredger may be provided with a pilot at the main or forward end to deflect debris encountered on the waterbed. The pilot may be a solid scoop to deflect debris above or below and / or to the side of the dredger. The pilot may be in the form of an angled screen which includes bars that allow water to pass through to ensure that the screen does not create excessive drag, but prevents debris from entering. The screens may be sized so that debris such as container retaining wires cannot enter the dredger, even at the end, but without creating excessive drag in the water. A pilot may also be provided on the upper surface of the dredger to protect the top of the dredger, even if it is not located at the front of the dredger. The pilot may include solid angled plates. Solid angled plates may be located in front of the injector pumps.

[0028] If the chassis is open, its rear end may be provided with bias flaps, which may be adjustable covers made of rubber, plastic or the like, to contain the sediments stirred up inside or under the chassis that are pushed out, deflecting them until they encounter a solid object or under a pressure threshold.

[0029] The dredging device may include a buoyancy compensator mounted on the vehicle, the buoyancy compensator maintaining the dredging device at the same level above the waterbed.

[0030] The extractor comprises a conduit and a pump arranged to pump agitated sediment through the conduit. The conduit may have a first opening exposed to the bottom surface of the sediment dredging device and a second opening located at the highest point of the sediment dredging device when in use. This arrangement ensures that the first opening is directed towards the agitated sediment and the second opening is raised at a certain level whereby the expelled sediment can be washed away by the natural movement of the water during use. The size and shape of the conduit will therefore depend on the intended use. For example, a longer conduit may be provided in a dredging device intended for use in a relatively deep harbor that is significantly deeper than the surrounding seabed, where the sediment must be deposited at a relatively higher level so that the tide can wash it away. It removes suspended sediment, while if this device is to be used in shallower waters such as a canal or a river-based port, the duct should be relatively shorter.

[0031] The relative height of the conduit can also be adjustable. The pipe can be replaced with pipes of different lengths or the length of the conduit can be adjusted. A conduit can be telescopic or have modular extensions that can be detachably connected. The angle of the conduit relative to the dredging device can also be adjustable to adjust the relative height of the conduit above the dredging device.

[0032] The shape of the conduit can also be varied so that, for example, a wider second opening may distribute the extracted sediment more widely than a narrower second opening. Thus, the conduit may be frustoconical, where the second opening is wider than the first opening, or the second opening may be grooved. The second opening may be divided into two openings.

[0033] The pumps may be provided with a power supply. Said power supply may be provided on the chassis or may be provided on a surface vehicle. The power supply may be provided with the dredging apparatus which may be fitted to an existing vehicle, or a vehicle may be fitted with an auxiliary power unit to power the pump or pumps. Power may be supplied to the pumps via a cable from the surface. The power may be supplied in the form of electricity or hydraulic pressure.

[0034] The device according to the present invention may be towed by a vehicle such as a boat across the waterbed. However, in certain circumstances, the vehicle may also be a land vehicle, for example if the water dredging is a canal. The sediment dredging device is therefore provided with an interface for connecting the sediment dredging device to the vehicle. The dredging device may also include a small crane which can be added to the vehicle for raising and lowering the dredging device in the water. In some embodiments, the dredging device may be provided with its own propulsion means.

[0035] The present invention also provides a dredging apparatus for being positioned above, but not in contact with, a waterbed to be dredged of sediment, the apparatus comprising: a chassis; a sediment agitator for being positioned above a layer of sediment on the waterbed, the sediment agitator comprising a fluid injector and a pump arranged to inject fluid through the fluid injector, the sediment agitator and pump mounted on the chassis; an extractor arranged to remove the agitated sediment from the waterbed and above the dredging apparatus, the extractor comprising a conduit and a pump arranged to pump the agitated sediment through the conduit, the extractor and pump mounted on the chassis, and an interface for connecting the sediment agitator to a vehicle.

[0036] The dredging apparatus may be as described in connection with the method of the present invention.

[0037] The invention also provides a use of the dredging apparatus described herein, wherein the use includes: suspending the dredging apparatus above, but not in contact with, the waterbed being dredged, extracting agitated sediments with the extraction apparatus, and settling the sediment of the extracted material underwater and above the dredging apparatus.

[0038] For the purpose of better understanding, the present invention will be described in detail by way of example only, and reference will be made to the following figures, in which:

[0039] Figure 1 shows a schematic representation of a dredging device according to the present invention.

[0040] Figure 2a shows a schematic cross-sectional end view of an alternative dredging device.

[0041] Figure 2b shows a schematic cross-sectional side view of the dredging apparatus of Figure 2a.

[0042] Figure 2c shows a schematic plan view of the dredging apparatus of Figures 2a and 2b.

[0043] Figure 3 shows a schematic view of a harbor and an illustration of a dredging device in use.

[0044] Figure 4 shows a front and perspective view of an alternative dredging device in accordance with the present invention.

[0045] Figure 5 shows a rear view and top perspective of the dredging apparatus of Figure 4.

[0046] Figure 6 shows a bottom perspective view of the dredging device according to Figures 4 and 5.

[0047] Figure 7 shows a side view of the dredging device according to Figures 4 to 6.

[0048] Figure 8 shows a front view of the dredging device according to Figures 4 to 7.

[0049] Figure 9 shows a top view of the dredging device according to Figures 4 to 8.

[0050] Figure 10 shows a front view of another example of a dredging device according to the present invention.

[0051] Figure 11 shows a cross-sectional view of the dredging apparatus of Figure 10 and

[0052] Figure 12 shows a front and top perspective view of the dredging apparatus of Figures 10 and 11.

[0053] Referring initially to FIG. 1, a schematic view of a dredging apparatus 100 is shown generally for use in a method according to the present invention. The dredging apparatus 100 includes a chassis shown generally at 110 and an extractor including a conduit shown generally at 120 and a pump 130, a sediment agitator shown generally at 140 and a pump 150, and an interface 160 for connecting a vehicle to the dredging apparatus 100. The dredging apparatus is designed to be disposed above and without contact with the waterbed from which the sediment to be removed is located. The sediment is then discharged by the extractor above the dredging apparatus 100 and into the upper water column. After being extracted by the extractor, the sediment is washed away by natural water movement, such as tidal movement or river flow.

[0054] Referring to Figures 2a through 2c, an alternative embodiment of a dredging apparatus is shown generally at 200. The dredging apparatus 200 includes a chassis generally at 210. The chassis 210 has a generally rectangular shape 211, a trailing long side 212, side sides 213, 214, a top surface 215, and a bottom surface 216. As is clearly shown in Figure 2a, the corner junction of the leading long edge 211 and the bottom surface 216 is flattened to form an angled side 217 so that the leading edge 211 is positioned above the bottom surface 216.

[0055] An injection pump 220 is mounted on the upper surface 215. The injection pump 220 is in fluid communication with a set of fluid injectors, indicated by the numeral 218, arranged to inject fluid below 216. The fluid injectors are arranged along the length of the chassis 210 between the side walls 213, 214 to inject fluid into the sediment used to stir it. The fluid injectors 218 may be positioned in a line that is adjacent to the angled side 217. The chassis 210 is substantially hollow and includes a conduit 219 from the injection pump 220 to the fluid injectors 218. The injection pump 220 also includes an inlet 221 for drawing water from the surrounding area during use prior to pumping it through the fluid injectors 218. In this case, the fluid is water, but in alternative embodiments it could be air or a mixture of air and water. The fluid, particularly if it includes air, can be pumped from the surface.

[0056] Mounted on the chassis 210 is an extractor pump, generally designated 230. The extractor pump 230 includes an inlet 231 for drawing water and agitated sediment from the surrounding area during use, which is then pumped out through an outlet that includes a conduit 240. The conduit 240 includes a generally conical chimney, although it can be substantially cylindrical or have a grooved or forked distal end for more widespread sediment distribution. Fluid drawn into the extractor pump 230 through the inlet 231 is discharged through the conduit 240. Although not shown, the injector pump 220 and the extractor pump 230 are powered by a power source, which can be mounted on the apparatus 200 or provided from the surface via a cable.

[0057] The injector pump 220 and the extraction pump 230 may be detachably connected to the chassis 210. The pumps in use are likely to be damaged by underwater debris, such as container retaining wires, and therefore if they are detachably connected, they may be replaced if they are damaged beyond repair during dredging operations. Thus, downtime can be reduced.

[0058] Runners 250 are arranged parallel along the side edges of the bottom portion 216 of the chassis 210. Runners 250 are connected to the bottom portion 216 of the chassis 210 by feet 251, which include shock absorbers (not shown). Runners 250 and the shock absorbers protect the chassis 210 if the chassis 210 inadvertently comes into contact with a waterbed during use. Alternatively, the feet may be solid and not include shock absorbers.

[0059] A pilot 260 is attached to the front plate 211 to deflect debris that may be towed by the dredging device while the water is in use.

[0060] An interface 270 is provided toward the front edge of the chassis 210 for connecting the dredging device 200 to a vehicle.

[0061] Referring now to FIG. 3, a schematic side view of a harbor is shown, generally indicated at 300, comprising a land generally indicated at 310, and a harbor wall indicated at 320, containing seawater therein, indicated at 330. The harbor floor 340 is located above which is a constructed sediment layer 350 that must be dredged. On the other side of the harbor wall 320 is the open sea, and as shown in FIG. 3, the sea floor 390 is relatively higher than the harbor floor 340. Tidal waters are able to enter and exit the harbor, but due to the relative difference in elevation of the harbor floor 340 and the sea floor 390, the sediment 350 at the bottom of the harbor floor 340 cannot be washed away, even if it is disturbed.

[0062] Dredging device 200, as described in connection with Figures 2a to 2c, is provided above, but not in contact with, sediment layer 350. Sediment dredging device 200 is towed by a boat 360 on water surface 330 above harbor floor 340 and above sediment layer 350. The boat includes a small crane and cable 370 connected to the interface 270 of the dredger 20, not only for raising and lowering the dredger 200 from the water, but also for towing the dredger 200 along the sediments 350. In this embodiment, a power supply 380 is provided on the surface of the boat 360 to supply power to the pumps 220 and 230 located on the device 200, although in alternative embodiments the boat may be provided with an auxiliary power unit that can directly power the pumps 220 and 230.

[0063] In use, the sediment dredger 200 is lowered from the boat onto the sediment, which is then placed 350 above the bottom of the harbor 340 by a crane 370. The injection pump 220 is operated by a control (not shown) and power supply 380 and pumps water 330 through an inlet 221 from the harbor 300 into a conduit 219 in the chassis 210 and out through fluid injectors 218 in the bottom 216 of the chassis 220 to agitate the sediment 350. The injection of water into the sediment layer 350 reduces the sediment density and also loosens the settled sediment 350. The extraction pump 230 then draws the loosened sediment 340 from the inlet 231 and discharges the sediment as shown in the plume 400 to a level above the seabed 390. Since the agitated sediment 400 is located in the water column above the seabed 390, the tidal water 330 entering and leaving the harbor 300 can extract the dislodged layer of sediment 400 and carry it away from the harbor.

[0064] Referring now to FIGS. 4-9, an alternative embodiment of a dredging apparatus is shown, generally designated 500. This dredging apparatus 500 may be used in the method of the present invention as described in connection with FIG. 3. The dredging apparatus 500 has a chassis including a frame, generally designated 510. The frame 510 includes a series of body components supported in a parallel arrangement by cross members. The advantage of this arrangement is that the frame is rugged and can withstand contact with the waterbed and underwater debris. Additionally, the "open" nature of the frame reduces drag in the water.

[0065] The body components of the frame 510 include opposing side walls 520 and body panels 530. The body panels 530 are spaced equidistant from the opposing side walls 520 and are substantially in the shape of the opposing side walls 520. The side walls 520 and the body panels 530 are connected by a cross member 540 extending below and forward of the side walls 520 and the body panels 530 and another cross member 550 extending below and rearward of the side walls 520 and the body panels 530. The undersides of the body panels 530 and the opposing side walls 520 include runners, generally designated 560. The runners 560 are provided to protect the frame 510 from contact with the waterbed during use.

[0066] Dredging apparatus 500 is provided with a fluid injector for injecting fluid into sediment in a water bed for the purpose of agitating and / or diluting the same. The injector includes a pair of injection pumps, generally indicated by the numeral 570, positioned at equal positions on either side of frame 510, the injection pumps 570 including inlets 580 in the form of conduits extending from the injection pumps 570 and positioned above the surface of frame 510 so as to draw water from the surrounding environment for injection into the sediment. The inlets 580 are positioned above frame 510 so as not to draw out sediment being removed by dredging apparatus 500. The injectors further include a pair of fluid outlets, generally indicated by the numeral 590. The fluid outlets 590 include a pair of parallel tubes 600, 610 extending between the upper front lips of the opposing side walls 520 and between the middle of the upper edge of the opposing side walls 520. The body panels 530 are also connected to the parallel tubes 600 and 610.Each tube 600, 610 includes a series of downwardly directed nozzles 620 through which fluid is injected into the sediment during use. Two nozzles 620 are provided between each side wall 520 and / or body panel 530, although this number may be increased or decreased accordingly. Each of the parallel tubes 600 and 610 is in fluid communication with the injector pump 570 through passages generally indicated by the numeral 630.

[0067] The dredging apparatus 500 further includes an extractor, generally indicated by the numeral 640, which includes an extraction pump 650 that, in use, draws agitated sediment from the bottom of the frame 510 and places it in a water column above the dredging apparatus 500. The extraction apparatus 640 further includes an extraction pipe 660 that is positioned between the side walls 520 at the upper rear corner thereof, thus providing additional support for the frame 510, and the extraction pipe 660 is also connected to the equally spaced hull panels 530. The extraction pipe 660 includes a series of downwardly facing openings 670 into which agitated sediment is drawn during use. The extraction pump 650 extends from an extraction duct 680 that is above the injector inlets 580. The extraction pump 650 and conduits 680 are securely attached to the frame 510. During use, the agitated sediment is drawn into the openings 670 that are poured onto the extraction tube 660, into the extraction pump 650, and then completely discharged through the extraction conduit 680.

[0068] The frame 510 and the injector pumps 570 are protected from underwater debris by a pilot in the form of screens 690 that are hingedly mounted on the rear top of the frame 510 and are wedged to deflect debris in the water above the frame 510. The leading edge of the opposite side walls 520 and body panels 530 are also rounded to deflect debris above or below the frame 510. The screens 690 are hingedly mounted to allow servicing of the injector pumps and pipes.

[0069] From the rear of the frame 510 between each body panel 530 and the side wall 520 are resiliently deformable covers 700, which may be made of rubber, plastic or the like. The covers 700 extend downward from the top of the frame 510, where they are attached to the frame, and reach the bottom of the frame 510, thereby enclosing the open back of the frame 510. The covers 700 are intended to agitate the sediment within the frame 510 for extraction by the openings 670 of the extraction device. However, if there is excessive sediment in the frame 510, such that pressure builds up within the frame to a certain point, or if an object such as a container or other heavy material enters the frame 510, it is sufficient to deform the covers 700 away from the frame 510 to expel the excess sediment or debris from the back of the frame 510.

[0070] The dredging device 500 is connected to the vehicle by a series of cables. Four cables 710, generally shown, are connected to connectors on the frame 510 on the extraction pump and are connected to a single cable (not shown) that is connected to a small crane at the rear of the vehicle (also not shown). This cable 710 is used to raise and lower the dredging device during use and to adjust its depth in the water. Other cables 720 are provided at the front of the dredging device 500 and are connected to the front of the opposing side walls 520. The cables 720 extend from under the vehicle and are connected at the front of the vehicle. These cables are provided to maintain the stability of the frame 510 during use and to maintain it at the correct depth. If the cables 720 are not provided at the front, the dredging device 500 may rise after encountering some sediment in the water.

[0071] The cables 710 may be connected to a buoyancy compensator on the vehicle, which maintains the dredging device at the same level above the waterbed during use.

[0072] The extraction and injector pumps 650, 570 in this embodiment are powered by power supplied from the vehicle, generally indicated by 730, and include a set of wires extending to a power source on the vehicle. The extraction and injector pumps 570, 650 will generally be electric. However, in some embodiments they may be hydraulic, in which case they also include a hydraulic hose or hoses leading to the vehicle.

[0073] Referring now to Figures 10-12, an alternative embodiment of a dredging apparatus is shown, generally designated 800 in accordance with the present invention. Dredging apparatus 800 is a variation of dredging apparatus 500 and thus similar reference numerals are used where appropriate. While dredging apparatus 500 is provided with a pilot in the form of screens 690 to protect the pumps from debris, dredging apparatus 800 is instead provided with angled plates 810 mounted on a chassis 820. Plates 810 may be formed of metal or other rigid material and angled to deflect debris away from the top of dredging apparatus 800. In particular, during use, dredging apparatus 800 may encounter metal container wires that are rigid. The 810 plates can deflect these wires, even if they hit the 810 plates.

[0074] The chassis 820 of the dredging device 800 is provided with a top panel 830 which is provided with covered openings 840 for access to the underside of the top panel 830.

[0075] A further difference compared to the dredging apparatus 500 is that the extraction duct 850 is bifurcated at its distal end so that the extracted sediment is discharged into the water over a wider area. The extraction duct 850 is supported by a frame 860.

[0076] Figure 11 shows a cross-sectional view through line XX as shown in Figure 10. This cross-sectional view shows the extraction tube 660 with the opening 670 and the parallel tubes 600, 610 on the fluid outlet 590 communicating with the nozzles 620. Figure 11 also shows the cross-members 540, 550 which are horizontally angled and have tapered edges to cut and deflect any debris that may be encountered during use.

Claims

Claims 1. A sediment dredging method comprising: suspending a dredging device from a vehicle, the dredging device comprising: a chassis; a sediment agitator for being positioned above a layer of sediment on a waterbed, the sediment agitator comprising a fluid injector and a pump arranged to inject fluid through the fluid injector, the sediment agitator and pump being mounted directly on the chassis, wherein the fluid injector comprises one or more conduits, the conduits comprising a plurality of nozzles; separately an extractor, arranged to remove agitated sediment from the waterbed and above the dredging device, the extractor comprising a conduit and a pump arranged to pump agitated sediment through the conduit, the extractor and pump being mounted directly on the chassis; and an interface for connecting the sediment dredging device to the vehicle; positioning the dredging device above, but not in contact with, the waterbed to be dredged of sediment; agitating the sediment with the sediment agitator; extracting the sediment with the extractor; suspending the extracted sediment underwater and into a higher water column above the sediment agitator; and movingDredging device around water; in which sediment is transported and deposited away from the area being dredged by the natural movement of water.

2. The method as claimed in claim 1, wherein the fluid injector is provided in the lower part of the sediment agitator device.

3. The method as claimed in claim 1 or claim 2, wherein the extraction duct has a first opening downwardly of the sediment dredging device and a second opening at the highest point of the sediment dredging device.

4. The method as claimed in claim 3, wherein the stacking duct is shaped and wherein the second opening is wider than the first opening.

5. The method as claimed in any one of the preceding claims, wherein the pumps are powered by a power supply provided on the vehicle.

6. A method as claimed in any one of claims 1 to 4, wherein the pumps are powered by a power source provided on the dredging device.

7. A method as claimed in any one of the preceding claims, wherein the dredging device and / or vehicle further comprises a pilot for deflecting debris present in the waterbed.

8. The method as claimed in any preceding claim, wherein the vehicle further comprises a buoyancy compensator, wherein the buoyancy compensator maintains the dredging device at the same level above the waterbed.

9. The method as claimed in any one of the preceding claims, wherein the chassis includes a shock absorbing device.

10. The method as claimed in claim 9, wherein the impact means comprises runners mounted on the underside of the chassis.

11. The method as claimed in any preceding claim, wherein the chassis comprises an open frame.

12. The method as claimed in any preceding claim, wherein the chassis comprises opposed side panels and one or more body panels extending parallel between the side panels, the body panel and the side panels being connected by one or more cross members.

13. The method as claimed in claim 12, wherein the one or more cross members comprise a sedimentation agitator, and wherein the sedimentation agitator comprises one or more conduits having one or more outlets for injecting fluid, the sedimentation agitator being in communication with one or more pumps, the pump being in communication with the inlet, and wherein the fluid is discharged from the surrounding area.

14. A method as claimed in claim 12 or 13, wherein the one or more cross members comprise an extractor, wherein the extractor comprises one or more inlet ducts into which the agitated sediment is drawn to be discharged, wherein the extractor is in communication with one or more pumps, wherein the pump is in communication with a duct raised above the dredging device for expelling the agitated sediment above the dredging device in use.

15. A sediment dredging apparatus for disposal above, but not in contact with, a waterbed from which sediment is to be dredged, the apparatus comprising: a chassis; a sediment agitator for disposal above a layer of sediment on a waterbed, the sediment agitator comprising a fluid injector and a pump arranged to inject fluid through the fluid injector, the sediment agitator and pump mounted directly on the chassis, wherein the fluid injector comprises one or more conduits, the conduit having a plurality of nozzles. Separately, an extractor, arranged to remove agitated sediment from the waterbed and above the dredging apparatus, the extractor comprising a conduit and a pump arranged to pump agitated sediment through the conduit and suspend the extracted sediment from the subsea to a higher water column above the sediment agitator, the extractor and pump being mounted directly on the chassis; and an interface for connecting the sediment dredging apparatus to a vehicle.

16. Use of a dredging device as claimed in claim 15, wherein the use comprises: connecting the dredging device to a vehicle with a connector; suspending the dredging device above, but not in contact with, the waterbed to be dredged; extracting the agitated sediment with an extractor device; and suspending the extracted sediment underwater and above the extractor device.

Images