GB2488809A

GB2488809A - Buoyant weir

Info

Publication number: GB2488809A
Application number: GB1104013.6A
Authority: GB
Inventors: Peter Miles Roberts
Original assignee: Verderg Ltd
Current assignee: Verderg Ltd
Priority date: 2011-03-09
Filing date: 2011-03-09
Publication date: 2012-09-12
Also published as: GB201104013D0

Abstract

The invention relates to a self adjusting weir 10 for use in a body of water that can be used to create a head rise in the body of water and autonomously rotate about a horizontal axis 26 in response to hydrostatic pressure exerted on the weir. The weir comprises a buoyant barrier 12 rotatably connected to a fixed support structure 14. The barrier has a downstream side 24, an upstream side 22, a base region 18 and a top surface 28, wherein the base region is rotatably connected to the support structure about an axis along the length of the barrier. The barrier may comprise a manifold 50 through which water can be introduced into the interior of the barrier. The barrier may comprise sealing members which co-operate with the support structure and scour skirts 46 attached to the base of the barrier.

Description

Buoyant Weir

Technical field

[0001] This invention relates to moveable weirs for use in flows of water. In particular the invention is directed to buoyant weirs that can be used to create a head rise in a body of water and autonomously rotate about a horizontal axis in response to hydrostatic pressure exerted on the weir.

Background art

[0002] The increase in the number of weirs, barrages and dams in bodies of waters such as rivers, streams, canals and estuaries is considered to increase the risk of damage that can be caused by flooding.

[0003] When there is a large discharge of water upstream, weirs, barrages and dams act as an obstruction to the flow of water down the river, and can increase the damage caused upstream as the water is prevented (or at least slowed) from flowing down the river and instead backs up behind the weir.

[0004] In addition to being an obstruction to the flow of water down the river themselves, weirs can also prevent debris, such as fallen branches and rubbish, from flowing uninterrupted down the river. The debris builds up behind the weir providing a further obstruction to the flow of water down the river.

[0005] Automatically opening and closing gates in weirs have been described that open to allow larger volumes of water than normal volumes to flow down the river. However current weirs comprise complicated systems to move the gates between an open and closed position in order to cope with excess flows of water.

[0006] For example EP03741 70 discloses a weir that that uses a separate floating counterweight connected to the weir gate by a cable. The counterweight is located upstream of the weir to sense any rise or fall in the water behind the weir. Pressure exerted on the counterweight from a rise in water level causes the gate to drop to provide an opening in the weir to water to flow through.

[0007] US2598389 describes a system having a gate comprising an upper gate and a lower gate. The lower gate extends into a lower chamber in the masonry of the weir with sufficiently close tolerances between gate and masonry to inhibit water ingress into the lower chamber. Water is admitted to the lower chamber through a duct when the water level rises behind the weir. The pressure of water applied to the lower gate in the chamber causes the gate to rotate about an axis extending between the upper and lower gate to lower the gate and allow water to flow through.

Disclosure of the invention

[0008] An object of the invention is to provide a simple cost effective weir that is able to control and direct the flow of water.

[0009] An aspect of the invention provides a self adjusting weir for use in a body of flowing water comprising a buoyant barrier and a support structure; the barrier having a downstream side, an upstream side and a top surface extending between the upstream side and the downstream side, wherein the base of the barrier is rotatably connected to the support structure about an axis; wherein in use, the extent of submersion of the barrier in the water is dependent upon the forces applied to the barrier; and wherein in response to changes in the moment of forces applied the barrier rotates about the axis to raise or lower the height of the barrier.

[0010] The tendency of a force to rotate an object about an axis is known as the moment. A number of moments contribute to the rotation of the barrier such as the moments of the total force of the integrated upstream pressure exerted on the barrier by the water, the total force of the integrated downstream pressure exerted on the barrier by the water, the force exerted on the top surface of the barrier by the water and the moment due to the barrier itself The moment of the barrier will depend upon its weight, weight distribution and shape. Thus for example a triangular shaped barrier connected to the support structure at a vertex on the base region such that the sides diverge will have a larger moment than a rectangular one of the same cross-sectional area and length from base region to top surface.

[0011] If the moment of the force on the upstream side of the barrier is dominating, the barrier will have a tendency to rotate about the axis in one direction. Conversely if the moment of the force on the downstream side of the barrier is dominating, the barrier will have a tendency to rotate about the axis in the reverse direction.

When the barrier is neither rotating to any significant extent in one direction or the other it may be termed as being at equilibrium, namely the moments responsible for rotation of the barrier are in equilibrium.

[0012] The barrier may be connected to the support structure at its base region.

[0013] In use, the support structure remains in a fixed position. It may be fixed to the ground underlying the water, such as a river bed, or to either side of the water such as a river bank. Fixing to the ground may be carried out for example by attaching to a concrete base or to piles driven into the river bed.

[0014] The flowing body of water may be in a river or estuary. The river may be tidal.

The body of flowing water may be fresh, salt or a mixture of both. The water flow may be laminar or turbulent due to factors such as eddies, recirculation, apparent randomness, flooding, tides and waves. The barrier may be provided in a tidal river wherein fresh water is flowing in one direction and sea water in another. Thus the hydrodynamics may be complex and consequently may modify the moments of the hydrostatic forces on the barrier.

[0015] The barrier may be connected to the support structure at an extremity, such as at a vertex.

[0016] The position of the barrier in the water is determined by the difference between the upstream pressure applied to the barrier and the downstream pressure applied to the barrier and the weight and dimensions of the barrier. When the barrier is at equilibrium, the downstream side is submerged to a greater extent than the upstream side. At least a portion of the downstream region of the top surface of the barrier may extend below the water level immediately downstream of the barrier and the position of the barrier is at an angle to the vertical. In response to an increase in the upstream pressure the downstream pressure the barrier can rotate about the horizontal axis to further submerge the barrier into the downstream body of water. In response to an increase in pressure applied to the downstream side the barrier can rotate upwards to lift at least a portion of the upstream region of the top surface of the barrier above the downstream water level.

[0017] Whilst not wishing to be bound by the theory of operation of the weir, it is believed that at normal flow speeds, hydrostatic forces and not hydrodynamic forces are principally responsible for rotation of the barrier. Hydrodynamic forces may contribute to the rotation of the barrier, for example skin friction forces dragging on the surface of the barrier and pressure forces normal to the barrier surface where the barrier changes the flow direction. At extreme flow rates, for example a flood situation creating a cascading avalanche of water bearing down on the barrier, the generation of hydrodynamic forces on the barrier may be become significant and even become dominant.

[0018] The axis of rotation may be parallel to the base of the barrier.

[0019] The barrier is typically elongate. The length of the barrier will depend upon the body of water to be controlled. The support structure may also be elongate. The barrier may be connected to the support structure by means of a single rotatable connection provided along the length the support structure, or a plurality of connections. The axis of rotation can extend substantially horizontally along the length of the base region of the barrier.

[0020] In some applications the barrier is connected to the support structure to allow rotation of the barrier through the vertical.

[0021] The cross sectional shape of the barrier can be substantially triangular, rectangular, or be irregular shaped. Irregular shapes can include T-shaped, P-shaped and lollipop shaped cross sections. The triangular cross section could be isosceles, scalene, equilateral or other triangular shapes. The upstream and downstream sides of the barrier may have differing areas of cross-section and shape. The upstream and downstream sides of the barrier may diverge from the point of connection at the support. However the cross sectional shape of the barrier will depend on the environment into which the barrier is to be installed.

[0022] A preferred shape for a barrier is substantially triangular wherein the barrier is connected to the support structure in the region of one of the vertices or one where the upstream and downstream sides diverge from the point of connection to the support structure.

[0023] The size, weight, shape, buoyancy and material forming the barrier can be selected such that in a standard river flow the barrier will be positioned in the desired equilibrium position when connected to the support structure. The selection of these parameters will determine the height (H) that the barrier extends above the river bed when it is at equilibrium. The size, weight, shape, buoyancy and material can be selected such that at equilibrium the downstream region of the top surface of the barrier extends below the downstream water level such that the barrier is at least partially submerged.

[0024] The barrier may typically be anywhere between five and several hundreds of meters in length and typically anywhere between 2 and I Sm in height from the connection point to the top surface of the barrier.

[0025] The barrier can be constructed from any suitable materials. For example the barrier material can be welded steel. In a triangular embodiment of the barrier a prismatic steel truss can be plated by thin steel plates. Alternatively the buoyant barrier could be constructed from hollow structural concrete or a hollow prismatic structure of reinforced glass, plastic or wood. It is preferred that the buoyant barrier is hollow, however the barrier is constructed from suitable materials that still enable the barrier to maintain its buoyancy in water.

Combinations of materials can be used. The barrier will be constructed to be water tight. As the barrier itself is buoyant, i.e. an integral buoyancy means, this simplifies the construction of the weir.

[0026] Water can be introduced into the barrier causing it to rotate such that it sinks into the water by increasing the effective self weight and self weight moment of the barrier. Thus the barrier may comprise inlet and outlets through which water may be received and removed. The barrier may comprise a manifold to supply and remove water. The barrier can be connected to a ballasting pump to assist in this process and provide manual operation of the weir if required. The ballasting pump can also be configured to remove water from the interior of the weir to reduce the effective self weight and raise the gate to a more upright position.

[0027] A manifold can be integral with the barrier through which water can be introduced into or removed from the interior of the barrier. The manifold can be connected to a pump. The manifold can be a hollow structural tubular member or a separate conduit or can be the barrier itself.

[0028] The end of the barrier can comprise sealing members to cooperate with the end of the support structure.

[0029] Skirts to minimise scour can be attached to the base of the barrier wherein the skirt extends along the length of the barrier. Skirts to minimise by pass flow can be attached to the base and ends of the barrier wherein the skirt extends along the length of the barrier.

[0030] During periods of exceptional high water volumes, storms or for other reasons, the barrier may be conveniently removed from being above the surface of the water by lowering it beneath the surface of the water. The base of the support structure or ground bed underlying the water can comprise a trench into which the barrier can be lowered when it rotates.

[0031] The weir or system comprising the weir may be used for the generation of energy. The weir or system may comprise one or more energy conversion devices to generate energy from flowing water.

[0032] The weir may further comprise instrumentation to provide information on the status of the barrier.

[0033] A second aspect of the invention comprises a method of generating energy from a body of water comprising: providing a weir according to the first aspect across a body of water; creating a bypass channel upstream from the weir to divert a volume water from the body of water through the by pass channel and back into the body of the river downstream of the weir; providing an energy converting device in the bypass channel; operating the device to generate energy from the water as it flows through the by pass channel.

[0034] Energy converting devices which may be used in the invention are well known and include those that convert the mechanical energy of flowing water into electrical energy or convert it into another form of mechanical energy, such as compression of a spring. The energy converting device may be a turbine. The electrical energy may be stored in an accumulator.

[0035] A third aspect of the invention provides a method of installing a weir according to the first aspect comprising providing a barrier that is rotatably connected to a support structure and immobilising the support structure to a fixed support structure.

[0036] A fourth aspect of the invention provides a system for providing energy comprising the weir for use in a body of flowing water according to the first aspect, a bypass channel upstream from the weir to divert a volume water from the body of water through the bypass channel and back into the body of the water downstream of the weir; and an energy converting device in the bypass channel to generate energy from the water as it flows through the bypass channel.

[0037] A key advantage is providing a buoyant barrier, namely one that floats in and is supported by the body of water so that is does not require a large supporting structure to support the barrier compared to a conventional structure such a sluice gate or dam. This supporting structure would vastly increase the overall weight of the weir and associated supporting structure. Furthermore the cumulative weight of water on a conventional barrier can create huge bending moments, especially for a barrier which is only supported at either end. As such conventional barriers need to be structurally reinforced to reduce the longitudinal bending moment. This also contributes to the overall weight of the structure and makes it more difficult to operate the barrier. Conversely the bending moment on a buoyant barrier is very much reduced and such lightweight low cost structures may be employed. A mass for the buoyant barrier may be in the region of 250kg/rn length. Furthermore such buoyant barriers may be supported more easily, for example regular supports along the length. Given that the barrier may extend several hundreds of metres, the weight and cost saving can be substantial.

Brief description of the drawings

[0038] The invention will now be described by way of example with reference to the accompanying drawings: Figures 1 and 2 show a side view of the invention; Figure 2 shows a plan view of the invention installed across a river; and Figure 3 shows a view of the invention installed across a river.

Detailed description of the invention

[0039] Figures 1 and 2 show a weir in accordance with the invention. The weir (10) comprises a buoyant barrier (12) that may be elongate and span across a width of the body of water. The barrier is rotatably connected to a fixed support structure (14) placed on the river bed (16). The barrier (12) rotates about an axis of rotation (26) that extends along the length of the base region (18) of the barrier. The barrier can rotate about the horizontal axis to raise or lower the height (H) of the barrier above the water level.

[0040] The barrier is rotatably connected at a lower corner at the base region (18) of the barrier (12). Types of rotatable connections to the support structure can include hinge members attached to the buoyant barrier or an axle extending through base area of the barrier. Other connections which allow the barrier to move about the horizontal axis can also be used.

[0041] The barrier may be attached to the support structure (14) by rotatable connections that extend continuously along the length of the support structure and barrier. In other embodiments of the barrier the rotatable connections can be spaced apart along the length of the support structure and barrier every 1 meter, 5 meters, 10 meters, 20 meters or other spacing as desired. The length of space between pivoting members can depend on the environment in which the barrier is installed and the strength of the barrier. The barrier may be attached to support structures at either end of the barrier. The weir may be supported by a support structure provided in the ground bed underlying the body of water.

[0042] Other constructions for the barrier include a substantially flat plate with buoyant tube extending along the top of the plate. The tube can be positioned symmetrically such that the central axis of the tube is colinear with the surface of the plate such that the cross sectional shape of the barrier is lollipop-shaped alternatively the tube centreline can be off-centre from the surface of the plate giving the barrier a "p" shaped cross-section.

[0043] Figure 1 shows an equilibrium position wherein the barrier (12) lies with its cross section at an angle (a) to the vertical (V). As shown a portion of the downstream region of the top surface (28) is below the downstream water level (32).

[0044] The size and shape of the barrier is preferably constructed such that the height of the barrier will be longer than the normal depth of the water on the upstream level (30) [0045] Where the weir (10) stretches across the width of a river (40) without any upstream exit points, the upstream water will rise and the buoyant barrier will rotate about the horizontal axis such that the barrier is lowered until the water flows over the top of the structure as shown in Figure 1 with a portion of the downstream region of the top surface (28) below the downstream water level (32).

[0046] As the flow rate increases more water will flow over the weir and the downstream river level will increase. A new equilibrium position for the buoyant barrier will be assumed which tends to maintain the head difference between the upstream and downstream water levels.

[0047] At higher flow rates hydrodynamic forces become significant and in effect increase the moment due to the weight of the buoyant barrage to the point where the barrier starts to sink into the downstream water. As shown in Figure 2 eventually the barrier will rotate sufficiently to adopt a new equilibrium position in which it lies substantially flat in the water and provides a substantially unobstructed passage for the water flow down the river which will allow a substantial flow volume to proceed downstream. In times of flood this release of water from the upper catchment area reduces the risk of flooding upstream from the weir.

[0048] As the flow rate from upstream decreases after a flood the hydrodynamic moments exerted on the barrier decrease and due to the buoyant nature of the barrier the barrier will begin to rise, until the moments from the self-weight and upstream pressure is again at equilibrium with the moment from the pressure exerted on the downstream side (24) and top surface of the barrier.

[0049] Debris flowing down a river can also increase the pressure exerted on the upstream side (22) of the barrier. As the barrier moves in response to the pressure exerted on it, the barrier will rotate about its axis if sufficient debris floats down the river and contacts the barrier with sufficient force. This will cause the barrier to rotate down into the water opening up a passage for the debris to continue flowing down the river. This helps in prevent debris getting caught behind the weir and causing further blockages in the river, that if not moved can increase the flood risk of the area.

[0050] As the barrier can move autonomously and self positions in response to changes in the balance of water pressures exerted on the barrier, the weir can respond more quickly to flood conditions than if manual intervention was required to lower the barrier during flood conditions.

[0051] Sealing members are provided at the end of the barrier to seal the space between the end of the barriers and the sides of the support structure or riverside structure to which the weir extends between. The sealing members cooperate with the sides of the support structure to prevent or at least inhibit by-pass leaks of water between the upstream side and the downstream side such that in a normal flow of water the upstream level of the river is maintained above the downstream level of the river.

[0052] Scour skirts (46) also acting as sealing members can extend from the barrier (12) to the river bed and/or floor of the support structure on one of both sides of the barrier. Skirts can also act as sealing members and be attached to the ends of the barrier. The skirts provide protection from the formation of scour channels and prevent or at least inhibit by pass flow. The skirts can be flexible to enable movement of the skirts as the barrier rotates.

[0053] The support structure can extend downstream out beyond the barrier and can comprise a trench on the floor of the support structure. When the barrier is rotated down into the water the barrier can lie in the trench providing an unobstructed passage down the river. Alternatively a trench (48) can be excavated into the river bed downstream of the barrier.

[0054] The support structure can comprise hold-down hinge points at regular spaces let into a river bed.

[0055] Positioning the barrier into a trench allows the barrier to lie substantially flat as the increased volume of water flows over the barrier, It also allows the barrier to keep out of the way and reduce the risk of debris, such as fallen branches, getting stuck behind the barrier and blocking the path of the water.

[0056] A manifold (50) can extend along the base region of the barrier to assist in flooding and deballasting of the barrier and to enable more accurate control of water distribution inside the barrier This ability to manually raise and lower the weir if needed is useful to provide an unobstructed passage for river traffic, fish or floating debris as required. The ability to manually ballast the barrier down is also useful when installing or removing the barrier from the river.

[0057] Figure 3 shows a cut away plain view of the weir installed across a river (40). A bridge (60) or other platform can extend across the river above the weir (10).

The weir is installed between the banks of the river. Upstream of the weir a bypass channel (54) has been installed to provide an upstream exit for the water. An energy conversion device (56) or water treatment plant can be installed in the bypass channel. In one embodiment the renewable energy device installed can be a Spectral Marine Energy Convertor (SMEC) device such as that described in W02008/01 5047 or GB patent application no. 1004321.4.

[0058] The weir (10) creates a head rise in the river such that energy can be converted as the water flows through the energy conversion device in the bypass channel.

[0059] Where there is an upstream exit point for the water, such as an exit channel, the upstream water level will fall in preferred applications as the abstraction rate through the exit channel increases. This will cause the buoyant barrier to rise as the pressure on the upstream side of the barrier decreases.

[0060] However under increasing downstream flow rates the upstream water level will increase in preferred applications to a depth where the water flows over the top of the barrier causing, the barrier to fall moderating the head rise.

[0061] If the abstracted water through the exit channel re-enters the river downstream of the buoyant weir the downstream water level will increase and the head rise will be modulated.

[0062] Figure 4 shows the weir (10) installed between the pillars of a single span bridge (60) extending across a river (40). The weir can extend across the entire width of the river as shown in Figure 3 between the pillars (62) of the bridge, or can extend only partially across the width of the river.

[0063] The weir can comprise a single barrier that extends across the width of the river. In other embodiments the weir may comprise a plurality of barriers to form the weir across the river. The barriers can be connected to a single support structure that comprises an elongate base fixed to the river bed or a plurality of support structures can be fixed to the river, the buoyant barrier rotatably connected to the structure.

[0064] Although the invention has been described with reference to a unidirectional flow the invention can be used where bi-directional flow may occur, for example in a tidal river or estuary. The buoyant barrier may rotate through the upright position and effectively flip over in the direction of the flow and therefore in a bidirectional flow the buoyant barrier can operate in the same manner when the direction of the water flow is reversed. A bi-directional SMEC device can be installed in the bypass channel allowing energy to be generated irrespective of the flow direction of water through the bypass channel.

[0065] Although the invention has been principally described with reference to the installation of the buoyant barrier across a river, it can also be installed in other bodies of water for example canals. It could also be used as an offshore artificial reef in coastal defence by breaking up water. It could be used to generate energy from wave power in the sea or coastal estuary.

[0066] Other changes can be made within the scope of the invention as would be evident to the skilled person.

Claims

Claims 1. A self adjusting weir for use in a body of flowing water comprising a buoyant barrier and a support structure; the barrier having a downstream side, an upstream side and a top surface extending between the upstream side and the downstream side, wherein the base of the barrier is rotatably connected to the support structure about an axis; wherein in use, the extent of submersion of the barrier in the water is dependent upon the force applied to the barrier; and wherein in response to changes in the moment of force applied the barrier rotates about the axis to raise or lower the height of the barrier.
2. A weir according to claim 1 wherein when the barrier is at equilibrium, the downstream side is submerged to a greater extent than the upstream side and at least a portion of the downstream region of the top surface barrier may extend below the water level immediately downstream of the barrier.
3. A weir according to claim I or claim 2 wherein in an equilibrium position the barrier tilts at an angle from vertical,
4. A weir according to any one of claims 1, 2 or 3 wherein the barrier is connected to the support structure to allow rotation of the barrier through the vertical.
5. A weir according to any one of claims I to 4 comprising a rotatable connection along the length of the support structure base and the barrier base.
6. A weir according to any one of claims I to 4 comprising rotatable connections spaced apart along the length of the support structure base and the barrier base.
7. A weir according to any one of claims I to 6 wherein the cross sectional shape of the barrier is substantially triangular, rectangular, or irregular shaped.
8. A weir according to claim 7 wherein the irregular shape is a T-shape, a P-shape or a lollipop shaped cross section.
9. A weir according to claim 7 wherein the cross sectional shape of the barrier is triangular.
10. A weir according to claim 9 wherein the barrier is rotatable connected to the support structure at a vertex of the triangle.
11. A weir according to any one of claims I to 10 wherein the barrier comprises a manifold through which water can be introduced into the interior of the barrier.
12. A weir according to claim 11 wherein the manifold is connected to a pump.
13. A weir according to any one of claims I to 12 wherein the end of the barrier comprises sealing members to cooperate with the end of the support structure.
14. A weir according to any one of claims 1 to 13 further comprising a skirt attached to the base of the barrier wherein the skirt extends along the length of the barrier.
15. A weir according to any one of claims Ito 14 wherein the base of the support structure comprises a trench into which the barrier can be lowered into.
16. A method of generating energy from a body of water comprising: providing a weir according to any one of claims 1 to 14 across a body of water; creating a bypass channel upstream from the weir to dived a volume water from the body of water through the by pass channel and back into the body of the river downstream of the weir; providing an energy converting device in the bypass channel operating the device to generate energy from the water as it flows through the by pass channel.