[0001] This invention is a method of agitating sediment, and apparatus, and the use thereof, to agitate sediment.

[0002] Fluvial processes relate to the movement of sediment in waterways and include the deposition of sediment on a waterbed. Harbours may be present in such waterways, and the build-up of sediment causes a problem because the deposition of sediment raises the level of the waterbed and creates an obstruction to shipping. In particular, the sediment may have a high shear strength which obstructs the keels of ships passing through the sediment.

[0003] Harbours are often deeper than the surrounding waterways, and sediment collects in the deeper areas. Harbours which are located on rivers are in particular affected by sediment brought downstream, and if the river is tidal, there is the further effect of sediment being brought from the sea into the harbour.

[0004] One way in which the sediment may be removed is by dredging. Dredging is generally defined as the underwater removal of sediment and its transport from one place to another. Dredging is a process which may comprise the steps of bringing sediment up from the surface of the waterbed, and optionally the steps of transporting the sediment away from the area being dredged, and then finally, disposal of the sediment. Optionally, the sediment may be loosened in the first instance.

[0005] Examples of prior art methods of dredging include a surface mounted grab or backhoe which can be used to physically lift sediment in a bucket, whereby the sediment is then placed into a hopper for subsequent disposal. A further prior art method utilises a trailing suction hopper dredger, which comprises a ship connected to a trailing drag head, wherein the sediment is pumped from the waterbed through the drag head to a hopper on the ship. Alternatively, the level of the waterbed may be levelled with an underwater plough.

[0006] Further prior art methods of dredging include the use of water injectors which inject water into the sediment to loosen it and reduce the density of the sediment, causing it to be suspended above the waterbed in a so-called “density cloud”. The suspended sediment is then washed away by gravity action. This method finds particular utility in rivers where the resulting density cloud of sediment can flow under gravity to deeper areas.

[0007] There are various problems associated with the prior art dredging methods. For example, water injection dredging requires that the water is flowing due to gravity in order to clear the suspended sediment, so is of little use in a coastal or tidal harbour where there is no gradient. Waterbed levelling does not remove any of the sediment, it merely flattens it, and the sediment can continue to build up over time. Trailing suction hopper dredgers, whilst often effective at clearing sediment, require purpose built and expensive equipment including a bespoke ship with a large hopper. Such equipment is not only expensive to acquire, but also to operate. Dredging with a grab arm and/or backhoe is also expensive as it requires the use of a specially adapted ship with a hopper to take away the dredged sediment.

[0008] Dredgers that are disposed on the waterbed are problematic in that the waterbed of a harbour, for example, is rarely flat and will contain lots of solid debris, making such dredgers impractical and easily damaged. Debris often encountered on the waterbed of a harbour includes container lashings, which comprise long metal poles which fall from containers as they are being loaded and unloaded. The container lashings can cause considerable damage to a dredger, and considerable time is then spent having to repair the dredger before it can be re-used, which has significant cost implications.

[0009] The present invention addresses the problems associated with the prior art by providing a method and apparatus that is not only efficient at addressing sediment on a range of different waterbeds, but is also relatively inexpensive to operate.

[0010] According to the present invention there is provided a method of agitating sediment comprising: suspending an agitating device from a vehicle, the agitating device comprising: a chassis; first agitating apparatus for disposal above a sediment layer on a waterbed, the first agitating apparatus comprising a fluid injector and at least one injector pump arranged to inject fluid through the fluid injector, the first agitating apparatus being mounted on the chassis; second agitating apparatus, comprising an inlet, one or more outlet and at least one extractor pump, the inlet being in communication with the extractor pump to extract agitated sediment and the one or more outlet being in communication with the extractor pump to reinject the extracted sediment back into the waterbed, the second agitating apparatus being mounted on the chassis; and a connector for connecting the agitating device to the vehicle; disposing the agitating device above, but not in contact with a waterbed having a sediment layer; agitating the sediment with the first agitating apparatus; extracting the sediment with the second agitating apparatus; reinjecting the extracted sediment back into the waterbed with the second agitating apparatus.

[0011] The method according to the present invention works by agitating, extracting and then re-agitating the sediment with the extracted sediment, which has been found to significantly reduce the shear strength of the sediment. In a harbour, this may mean that whilst sediment levels may raise to levels such that the sediment comes into contact with the keels of ships, the reduction in shear strength is such that the ships can pass freely through the sediment. Whilst this method might not remove the need for dredging altogether, it means that the number of dredging operations will be significantly reduced, thus saving money. [0012] By having the agitating device operate above the level of the waterbed, the device is able to mitigate the problems associated with many prior art devices by avoiding much of the debris and being able to traverse uneven waterbeds.

[0013] The agitating device may employ a range of different sediment agitating means in addition to a fluid injector. The first agitating apparatus further comprises one or more injector pump, wherein the injector pump injects fluid through the fluid injector into the sediment to loosen the sediment prior to extraction. The fluid injector and one or more injector pump are mounted to the chassis. The fluid injector may be disposed towards an underside of the agitating device. In particular, the fluid injector may comprise an outlet positioned so as to expel fluid in a downward direction during use into the sediment disposed on the waterbed. More than one fluid injector may be provided, and an array of fluid injectors may be provided. The fluid injector may comprise one or more conduit, the conduit bearing a plurality of outlets or nozzles. The outlets or nozzles may be spaced evenly along the conduit. A plurality of conduits may be provided in a parallel arrangement along the width of the chassis. The one or more conduit may span the entire width of the chassis. A plurality of injector pumps may be provided, with one pump provided per fluid injector or per plurality of fluid injectors. The fluid being injected may be water or air or a combination thereof. The fluid injector may further comprise an inlet in communication with the injector pump, and in use fluid will be drawn from the surrounding area. In use, this fluid will normally comprise water. Alternatively, the fluid may be provided from the surface or from the vehicle to the agitating device.

[0014] Prior art devices that pump fluid to agitate sediment will generally use high pressure jets. High pressure in the art is defined as 800-1000 kPa (8-10 bar). Conversely, the fluid injected by the dredgers according to 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 has been found to be advantageous over high pressure jets, as it requires fewer resources in terms of pump pressure and power use and is effective at agitating sufficient amounts of sediment.

[0015] The second agitating apparatus comprises an inlet, one or more outlet and at least one extractor pump, the inlet being in communication with the extractor pump to extract agitated sediment and the one or more outlet being in communication with the extractor pump to reinject the extracted sediment back into the waterbed, the second agitating apparatus being mounted on the chassis. Both the inlet and the one or more outlet of the second agitating apparatus may be disposed towards an underside of the agitating device. The inlet may comprise a conduit comprising one or more opening exposed to the underside of the agitating device, which conduit is in communication with the extractor pump. In use, agitated sediment is drawn in through the one or more opening, through the conduit and into the pump. The outlet may comprise a conduit extending from the extractor pump to the underside of the agitating device. The conduit of the outlet may be bifurcated.

[0016] The chassis may have a generally planar, solid base, or alternatively 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 comprise side walls and an upper surface on which items such as the first and second agitating apparatus are provided. The front and back of the frame may be “open” which will allow for heavy material and debris, which otherwise would damage the agitating device, to pass through the agitating device. Furthermore, having an open frame will reduce the drag on the chassis as it moves through the water, thereby allowing for an agitating operation to proceed at a faster rate than would be possible with prior art devices.

[0017] The chassis may comprise opposed side panels, and wherein one or more cross member may be disposed between the opposed side panels. Further, to provide further support, one or more body panel may be disposed in parallel between the side panels connected to the one or more cross member.

[0018] The one or more cross member may comprise one or more of the fluid injector of the first agitating apparatus, the inlet of the second agitating apparatus or the outlet of the second agitating apparatus. The cross member, if comprising the fluid injector of the first agitating apparatus may comprise a pipe or conduit bearing outlets or nozzles. The cross member, if comprising the inlet of the second agitating apparatus may comprise a pipe or conduit having an opening. The cross member, if comprising the outlet of the second agitating apparatus may comprise a pipe or conduit bearing one or more opening.

[0019] At least three cross members comprising the fluid injector of the first agitating apparatus, and the inlet and the outlet of the second agitating apparatus, may be disposed in a parallel arrangement between the side panels. There may be provided more than one of each of the fluid injector of the first agitating apparatus, and the inlet and the outlet of the second agitating apparatus.

[0020] The cross members may be disposed in any arrangement. For example, the fluid injector of the first agitating apparatus may be disposed at a leading edge of the agitating apparatus, the outlet of the second agitating apparatus may be disposed at a rear edge of the agitating apparatus, and the outlet of the second agitating apparatus might be disposed in between. Therefore, when the agitating apparatus is pulled across and above the waterbed by the vehicle, an area of sediment may first be agitated by the fluid injector of the first agitating apparatus, then be extracted by the inlet of the second agitating apparatus, and then reinjected into the same area by the outlet of the second agitating apparatus.

[0021] The one or more cross member may also comprise a rigid support bar disposed towards a leading edge of the agitating device. The rigid support bar may comprise a tapered leading edge to cut through any sediment encountered during use.

[0022] The present agitating device in use operates above and apart from the waterbed, however the chassis may be suitably robust in order to withstand contact with the waterbed. This may occur when the agitating device is being 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 undulating.

[0023] The chassis may comprise shock absorbing means to protect the agitating device if it collides with the waterbed and/or debris which it may encounter during use. For example, the chassis may be provided with buffers mounted on the underside of the chassis, or alternatively may comprise heavy- duty runners to protect the underside of the chassis. Runners may be disposed beneath the chassis and/or the side panels. A leading edge of the chassis and/or side panels may be rounded so as to deflect debris.

[0024] The agitating device may be provided at a leading end, or front, thereof with a pilot to deflect debris encountered on the waterbed. The pilot could be a solid scoop to deflect debris either above or below and/or to the side of the dredging apparatus. The pilot may be in the form of an angled grille comprising bars to allow water to pass therethrough to ensure that the grille does not produce too much drag, but which prevents ingress of debris. The grilles may be sized appropriately so that debris such as container lashings cannot enter the dredging apparatus, even end-on, but without causing too much drag in the water. A pilot may also be disposed on the upper surface of the dredging apparatus to protect the top of the dredging apparatus, even if not provided on the front of the dredging apparatus. The pilot may comprise angled solid plates. The angled solid plates may be disposed in front of the injector pumps.

[0025] If the chassis is open, the rear end thereof may be provided with biased flaps, which may be deformable mats made from rubber, plastic or the like, to keep agitated sediment inside or beneath the chassis to be expelled, but which will deform if they encounter a solid object or reach a threshold of pressure from within the agitating apparatus. [0026] The agitating device may further comprise a swell compensator disposed on the vehicle, the swell compensator maintaining the agitating device at the same level above the waterbed.

[0027] The pumps may be provided with a power supply. Said power supply could be provided on the chassis or could be provided on an above-surface vehicle. Power packs may be provided with the agitating device, which can be retrofitted on to an existing vehicle, or a vehicle could be adapted to include an auxiliary power unit to provide power to the pump or pumps. Power could be provided to the pumps via a cable from the surface. Power could be provided in the form of electricity or hydraulic pressure.

[0028] The agitating device according to the present invention may be towed across the waterbed by a vehicle such as a boat. However, in certain situations the vehicle could also be a land-based vehicle for instance if the water being dredged is a canal. The agitating device is therefore provided with a connector for connecting the agitating device to a vehicle. The agitating device may also include a winch which can be retrofitted to a vehicle to raise and lower the agitating device in the water. In some embodiments, the agitating device could be provided with its own propulsion means.

[0029] The present invention also provides an agitating device for disposal above, but not in contact with, a waterbed to agitate sediment, the device comprising: a chassis; first agitating apparatus for disposal above a sediment layer on a waterbed, the first agitating apparatus comprising a fluid injector and at least one injector pump arranged to inject fluid through the fluid injector, the first agitating apparatus being mounted on the chassis; second agitating apparatus, comprising an inlet, one or more outlet and at least one extractor pump, the inlet being in communication with the extractor pump to extract agitated sediment and the one or more outlet being in communication with the extractor pump to reinject the extracted sediment back into the waterbed, the second agitating apparatus being mounted on the chassis; and a connector for connecting the agitating device to a vehicle.

[0030] The dredging apparatus may be as described in relation to the method of the present invention. [0031] The present invention also provides use of the agitating device as previously described, wherein the use comprises: connecting the agitating device to a vehicle with the connector; suspending the agitating device above, but not in contact with a waterbed; agitating the sediment with the fluid injector of the first agitating apparatus; extracting the agitated sediment with the second agitating apparatus and reinjecting the extracted sediment back into the waterbed with the second agitating apparatus.

[0032] So that it may be better understood, the present invention will now be described in detail but by way of example only, with reference to the following Figures, in which:

[0033] Figure 1 shows a flow chart of the method according to the present invention;

[0034] Figure 2 shows a perspective view of an agitating device according to the present invention;

[0035] Figure 3 shows the side view of the agitating device of Figure 2;

[0036] Figure 4 show a rear view of the agitating device of Figures 2-3;

[0037] Figure 5 shows a rear perspective view of the agitating device of Figures 2-4; and

[0038] Figure 6 shows an alternative rear perspective view of the agitating device of Figures 2-5.

[0039] With reference initially to Figure 1 there is shown a flow diagram of the present method of agitating sediment. At Step 110, there is shown the step of suspending an agitating device from a vehicle, the agitating device comprising: a chassis; first agitating apparatus, which is for disposal above a sediment layer on a waterbed, the first agitating apparatus comprising a fluid injector and at least one injector pump. The injector pump is arranged to inject fluid through the fluid injector. The first agitating apparatus is mounted on the chassis. The agitating device further comprises second agitating apparatus, comprising an inlet, one or more outlet and at least one extractor pump. The inlet is in communication with the extractor pump to extract agitated sediment and the one or more outlet is in communication with the extractor pump to reinject the extracted sediment back into the waterbed, the second agitating apparatus being mounted on the chassis. The agitating device further comprises a connector for connecting the agitating device to a vehicle.

[0040] At Step 120, the method comprises disposing the agitating device above, but not in contact with a waterbed having a sediment layer. At Step 130, the method comprises agitating the sediment with the first agitating apparatus. At Step 140 the method comprises extracting the sediment with the second agitating apparatus and at Step 150 the method comprises reinjecting the extracted sediment back into the waterbed with the second agitating apparatus.

[0041] With reference now to Figures 2 to 6, there is shown an agitating device generally indicated 200 comprising a chassis generally indicated 210, first agitating apparatus generally indicated 220 and second agitating apparatus generally indicated 230. The agitating device 200 further comprises a connector 240 for connecting the device to a vehicle.

[0042] The chassis 210 comprises opposed side panels 250, and a series of spaced apart parallel body sections 260. The chassis 210 further comprises an upper surface 270 and a base 280. The side panels 250 and the parallel body sections 260 are connected with a cross member 290 at a front edge of the agitating device 200.

[0043] The first agitating apparatus 220 comprises two injector pumps 300 which comprise inlets 310 that draw water in from the surrounding area when in use. Extending from the injector pump 300 is an outlet 320 which bifurcates into two fluid injection conduits 330 which extend the width of the agitating device 200 and connect the side panels 250 and the parallel body sections 260. As shown on Figure 2 nozzles 340 extend from beneath the fluid injection conduits 330 in a spaced-apart arrangement.

[0044] The second agitating apparatus 230 comprises an extractor pump 350 mounted onto the chassis 210. The second agitating apparatus 230 comprises an inlet generally indicated 360 in communication with the pump. As best shown in Figures 4 to 6, the inlet 360 comprises a conduit 370 that extends the width of the agitating device 200 joined to the extractor pump 350 with connecting pipe 380. Although not shown here, the conduit 370 comprises a plurality of openings disposed towards the underside of the agitating device 200. An outlet generally indicated 390 is in communication with the extractor pump 350. The outlet 390 comprises a first pipe 400 that extends from the pump 350 and bifurcates into two further pipes 410 which extend to an injector conduit 420 disposed at the rear of the agitating device 200. As best shown in Figures 3 to 6, the injector conduit comprises a series of spaced apart openings 430.

[0045] In use, the agitating device is suspended from a vehicle from the connector 240 and is disposed above but not in contact with a waterbed having a sediment layer. The sediment is agitated with the first agitating apparatus 220. The injector pumps 300 draw liquid from the surrounding area through the inlets 310 and pump the liquid through the outlet 320 and into the fluid injector conduits 330. The pressurised water is expelled through the nozzles 340 into the settlement to liquefy and agitate it. The agitating device 200 is pulled across the waterbed by the vehicle, and the second agitating apparatus 230 firstly extracts the agitated sediment through openings in the conduit 370. The extracted sediment is drawn into the connection pipe 380 by the extractor pump 350. The extracted sediment is then expelled by pump 350 through outlet 390. In particular, the extracted sediment is pumped through first pipe 400 and into the two further pipes 410 to the injector conduit 420 where the extracted sediment is reinjected into the sediment in the waterbed through openings 430. The second agitation of the sediment in the waterbed with the first agitating apparatus 220 and the second agitating apparatus 230 reduces the shear strength of the sediment sufficiently that vessels passing through the water that come into contact with the sediment are not impeded by the sediment.