Various types of crest gates exist for modifying the water level in a reservoir. Some of these gates allow for an additional quantity of water to be stored in the reservoir, and for the relatively rapid discharge of the additional quantity of water from the reservoir in the event of a flood.

However, a problem associated with many of the known crest gates is that they are not fully automatic, and generally have to be controlled either manually or electrically.

SUMMARY OF THE INVENTION According to the invention there is provided a water control gate comprising: a variable ballast tank defining a movable barrier ; a pivot arrangement for connecting the movable barrier to a spillway so that it can pivot between an upper closed position, in which it projects above the crest of the spillway so as to effectively increase the height thereof, and a lower open position ; a water inlet communicating with the ballast tank for allowing water into the tank when the water level in a reservoir associated with the spillway rises above a predetermined level, thereby causing the ballast tank to pivot downwardly towards the open position in which water in the reservoir is allowed to flow over the movable barrier and out of the reservoir; and a water outlet communicating with the ballast tank for allowing water in the tank to be drained therefrom so as to cause the tank to pivot upwardly towards the closed position.

In the preferred form of the invention, the water control gate includes a counterweight to assist in the movement of the movable barrier from the closed position towards the open position.

The counterweight may be located within the ballast tank, and may be in the form of a mass of steel or concrete.

Preferably, the movable barrier extends between two false piers projecting above the crest of the spillway, and a series of water seals are provided between the barrier and the piers, and between the barrier and the spillway to prevent water in the reservoir from flowing past the barrier in these regions.

Typically, the false piers include stops which are arranged to interact with the movable barrier so as to prevent the movement of the barrier past a selected closed position.

The water control gate may include damping means in the form of a plurality of hydraulic cylinders for controlling the rate at which the movable barrier opens and closes. These hydraulic cylinders may also serve to restrain the movement of the movable barrier beyond the selected closed position.

Preferably, the gate includes an air line for allowing air within the tank to be expelled when the tank is filled with water, and for allowing air to be drawn into the tank when water in the tank is drained therefrom.

The air line may include a water drain pipe for draining any water which may enter the line, thereby to prevent a water seal from developing within this line.

Conveniently, the water outlet is designed so that, when water flows through the outlet, a siphon effect is developed in the outlet and water in the ballast tank is sucked out of this tank. Alternatively, a pump arrangement may be used for this purpose.

The inlet and the outlet may include valves for controlling the flow of water therethrough.

A resilient stopper may be provided on the spillway to protect the movable barrier and the spillway when the movable barrier moves into the open position. The resilient stopper may be formed from synthetic rubber and may extend from one of the piers to the other.

Preferably, the pivot arrangement is in the form of a series of hinges extending longitudinally along the spillway.

The ballast tank may include an internal baffle plate for separating the tank into two internal compartments. In this way, the buoyancy of the tank is modified so as to facilitate the movement of the tank between the closed and the open positions.

The control gate may also include a vent pipe for preventing the development of excessive pressures within a chamber formed between the movable barrier and the spillway when the movable barrier is in the open position.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows, diagrammatically, a plan view of the water control gate of the invention mounted on a spillway; Figure 2 shows, diagrammatically, a front view of the water control gate of Figure 1, with certain features omitted for clarity; Figure 3 shows a cross-sectional view of the water control gate, in a closed position, along the line 3-3 of Figure 2, with certain features omitted for clarity ; Figure 4 shows a cross-sectional view similar to that of Figure 3 but with the gate in an open position ; Figure 5 shows a cross-sectional view similar to that of Figure 3 illustrating the water inlet ; Figure 6 shows a cross-sectional view similar to that of Figure 5 but with the gate in an open position; Figure 7 shows a cross-sectional view similar to that of Figure 3 illustrating the water outlet; Figure 8 shows a cross-sectional view similar to that of Figure 7 but with the gate in an open position; Figure 9 shows, diagrammatically, a plan view of a second embodiment of the water control gate of the invention mounted on a spillway; Figure 10 shows, diagrammatically, a front view of the water control gate illustrated in Figure 9, with certain features omitted for clarity; Figure 11 shows a cross-sectional view of the second embodiment of the water control gate, in a closed position, along the line 11-11 of Figure 10, with certain features omitted for clarity ; Figure 12 shows a cross-sectional view similar to that of Figure 11 but with the gate in an open position; Figure 13 shows a cross-sectional view similar to that of Figure 11 illustrating the water inlet ; Figure 14 shows a cross-sectional view similar to that of Figure 13 but with the gate in an open position; Figure 15 shows a cross-sectional view similar to that of Figure 11 illustrating the water outlet ; Figure 16 shows a cross-sectional view similar to that of Figure 15 but with the gate in an open position; and Figure 17 shows a cross-sectional view similar to that of Figure 16, illustrating a vent pipe for preventing the development of excessive pressures within a chamber formed between the movable barrier and the spillway when the movable barrier is in the open position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Figures I and 2 of the drawings, there is shown a water control gate 10 comprising a movable barrier in the form of a pair of cylindrical ballast tanks 12 attached to a spillway 14 by means of a plurality of hinges 16.

The hinges 16 extend longitudinally across the top of the spillway, as shown, so that the pivot axis about which the ballast tanks pivot is substantially horizontal. The ballast tanks 12 are formed from mild steel and have relatively smooth side walls.

The tanks 12 extend between two false piers 18 and are spaced from one another and from the false piers by means of water seals 20. There is also a water seal 20a (see Figure 3) between the ballast tanks 12 and the spillway 14. The water seals 20 and 20a are designed to allow the ballast tanks to move relative to the spillway and the false piers without allowing water in a reservoir 21 associated with the spillway 14 to flow between the tanks and the spillway, between the tanks and the false piers, or between the tanks themselves.

A pair of water inlet pipes 22 are embedded in the false piers 18 and extend upwardly from the ballast tanks 12, as shown most clearly in Figure 2. The water inlet pipes 22 have open upper ends 24, through which water can enter the pipes, and lower ends 26 connected to the ballast tanks through which water can enter the tanks.

The ballast tanks 12 are also connected to the upper ends 28 of water outlet pipes 30. The outlet pipes 30 run along the spillway 14 to lower ends 32 where water from the tanks can be discharged.

An air line 34 runs along the inside of each inlet pipe 22 for allowing air to be drawn into, or expelled from, the tanks. The air lines extend from within the ballast tanks 12 to a point above open upper ends 25 of the water inlet pipes With reference now to Figure 3 of the drawings, a mass of concrete 36 is fixed to a portion of the inner surface of each ballast tank 12 so as to form an eccentric internal counterweight within each tank. The counterweights oppose some of the forces applied to the tanks by the water in the reservoir 21, and facilitate the operation of the gate in a partially opened condition.

The counterweights also serve to strengthen the walls of the ballast tanks The ballast tanks are arranged to pivot from a closed position, as illustrated in Figure 3 of the drawings, in which the tanks project above the crest of the spillway 14, to an open position as illustrated in Figure 4. A series of swivel coupling 37 connect the ballast tanks to the inlet pipes 22 and the outlet pipes 30 so as to allow the tanks to pivot relative these pipes.

To limit the speed with which the ballast tanks open and close, a plurality of damping means in the form of hydraulic cylinders 38 are connected to the ballast tanks 12 and the spillway 14 The hydraulic cylinders also limit the extent to which the ballast tanks can close, so as to prevent the ballast tanks from pivoting past the closed position. Furthermore, a series of rubber stoppers 40 are mounted on the spillway, as shown, to prevent unnecessary damage due to impact between the ballast tanks and the spillway when the ballast tanks move into the open position.

Referring now to Figures 5 and 6 of the drawings, when the ballast tanks 12 are in the closed position (Figure 5) the tanks projects above the crest of the spillway 14. The seals 20 and 20a prevent water which flows into the reservoir 21 from flowing past the tanks 12, so that as water flows into the reservoir and the level of the water increases above the crest of the spillway, the buoyant tanks are pivoted on the water surface into the closed position.

As mentioned above, the counterweights 36 assist the ballast tanks in resisting the forces exerted on them by the water in the reservoir.

When the level of the water reaches the apex of the control gate 10 in its closed position, it simultaneously reaches the open ends 24 of the inlet pipes 22. A further increase in the level of the water causes water to flow into the water inlets 22, through these inlets and into the tanks 12. As the water flows into the ballast tanks 12, the air inside these tanks is expelled through the air lines 34, and the increase in the volume of water in these tanks results in an increase in the total mass of the tanks. The design of the tanks is such that, when a predetermined volume of water has entered the tanks, they no longer remain buoyant in water and accordingly pivot downwardly towards the open position.

As the ballast tanks 12 submerge, the water in the reservoir flows over the top of the control gate 10 and out of the reservoir 21. The mass of the counterweights 36 assist the ballast tanks in moving from the closed position towards the open position, while the hydraulic cylinders 38 prevent the ballast tanks from pivoting too fast and thereby causing damage to either the tanks or the spillway due to impact loads.

Since the sides of the cylindrical ballast tanks 12 are relatively smooth, tree branches and other floating debris which contact the tanks as they flow over the top of the gate 10 will generally flow past the tanks unhindered and will not become entangled on the tanks.

Figure 6 illustrates the control gate 10 in a fully open condition in which the water in the reservoir is free to flow over the spillway. It will be appreciated that, when large volumes of water flow into the reservoir, such as during a flood, the water can be discharged relatively quickly from the reservoir by the opening of the control gate as described above.

If the intention is to retain the additional volume of water that accumulates in the reservoir when the control gate is in the closed position, the hydraulic cylinders 38 can be locked in their extended position so that, even when the ballast tanks 12 fill up with water, the control gate is held in the closed position.

With reference now to Figures 7 and 8, as water flows through the outlet pipes 130, a siphon effect is developed in these pipes so that water in the ballast tanks 12 is sucked out of the tanks-Alternatively, this water can be pumped out of the ballast tanks, if desired. The air lines 34 allow air to be sucked into the tanks 12 as the water is discharged from these tanks, and in this way, the total weight of the ballast tanks is reduced until the tanks are once again buoyant in water. When this occurs, the tanks pivot back towards the closed position.

The counterweights 36 together with the hydraulic cylinders 38 prevent the ballast tanks from pivoting into the closed position too quickly and thereby avoid the development of shock loads when the tanks reach the closed position.

As the ballast tanks 12 pivot back into the closed position, the effective height of the spillway is once again increased, and consequently the water level in the reservoir once again rises. Thus, by pivoting between the closed and open positions, the water control gate controls the level of water in the reservoir.

Valves may be provided on the inlet pipes 22 and the outlet pipes 30, if desired, to control the flow of water through these pipes. For example, float valves, level control valves, sluice valves or butterfly valves may be used for this purpose.

Although in the embodiment described above the ballast tanks are formed from mild steel, these tanks may also be formed from other materials such as stainless steel, fibreglass, plastics materials, high density polyethylene, or even reinforced concrete.

A second embodiment of the invention is illustrated in Figures 9 to 17 of the accompanying drawings. With reference first to Figures 9 and 10, a water control gate 110 can be seen to include a ballast tank 112 which is formed from mild steel and which is connected to a spillway 114 to form a movable barrier on the spillway.

The ballast tank 112 is pivotally attached to the spillway by means of a series of hinges 116 in a similar fashion to that described above with reference to the first embodiment of the invention. The tank extends between two false piers 118 and is separated from each pier by means of a water seal I20. The tank is also separated from the spillway 114 by means of a water seal 122 so that water is prevented from flowing past the tank, between the tank and the piers or between the tank and the spillway.

A water inlet pipe 124 passes through one of the piers, as shown, and extends from an inlet end 124A, located at a predetermined level above the tank 112, to an outlet end 124B located in the tank. In this way, water entering the inlet end 124A flows towards the outlet end 124B and is introduced into the tank through this end. A valve 126 is connected to the water inlet pipe 124 at a level below the inlet end 124A. The purpose of this valve is to selectively allow water to enter the inlet 124 when the level of the water in the reservoir is not high enough to enter the inlet end 124A. In this way, the water control gate can be controlled manually, if desired.

The tank 112 is also connected to a water outlet pipe 128 at a ballast tank outlet 128A. The pipe 128 is partially embedded in the spillway 114 and extends to an outlet opening 128B located on the spillway. The outlet pipe 128 includes a valve 129, as illustrated, for controlling the flow of fluid through this pipe.

An air line 130 connects the inside of the tank 112 to ambient air so that air can be drawn into or expelled from the tank through this air line. As can be seen most clearly in Figure 10 of the drawings, the air line 130 includes a portion 130A which is embedded in one of the piers 118 and which communicates with ambient air via an upper end 132. The other end 134 of the pipe 130 is located within the tank 112, as shown. A water drain pipe 136 extends from the air line 130 through the spillway 114 to a water outlet end 136A. The drain pipe is connected to the air line 130 immediately before the air line enters the tank 112, and serves to prevent the development of a water seal in the air line by allowing water which enters this line to be discharged therefrom. In this way, a clear path is maintained along the line 130 for air to move freely into and out of the tank 112.

Figures 11 and 12 show cross-sectional views of the control gate 110, together with the air line 130 and the drain pipe 136. In Figure 11, the drain pipe 136 can be seen to be connected to the air line 130 along a lower portion thereof so that any water entering the air line and collecting at this lower portion is drained from the air line via the drain pipe 136.

The control gate 110 also includes a pair of stops 138 connected to the two piers 118. As can be seen in Figure 11, the tank 112 bears directly against the stops 138 in the closed position, and is prevented from rotating upwardly beyond the closed position by the stops.

A lower stopper is also provided in the form of an elongate, longitudinally extending strip 140 which extends along the length of the spillway 114 between the two piers 118.

As in the case of the first embodiment of the invention, in this embodiment the tank 112 also includes a counterweight 142 which is designed to facilitate the movement of the tank between the closed and the open positions. However, in this embodiment, the counterweight comprises a mass of mild steel and concrete. The tank also has a baffle plate 143 which separates the inside of this tank into two internal compartments 143A and 143B. The baffle plate includes an opening 144 at an upper end thereof for allowing air to flow between the two compartments.

Figures 13 and 14 illustrate the control gate 110 in cross-section, together with the water inlet 124. When the water level in the reservoir rises above the upper end 145 of the water inlet, it flows through the inlet directly into the compartment 143A. The compartments 143A and 143B are connected to one another by an opening 146 so that, as water accumulates in the compartment 143A, it flows through the opening 146 and into the compartment 143B- Figures 15 and 16 show. in cross-section, how the water outlet 128 runs from the ballast tank outlet opening 128A through the spillway 114 to the outlet opening 128B.

A vent pipe 147, illustrated in Figure 17 of the drawings, connects the water adjacent the spillway 114 to ambient air via one of the piers 118, as shown.

The pipe 147 is also illustrated in Figures 9 and 10 of the drawings. In Figure 17, the ballast tank 112 can be seen to be spaced from the top of the spillway 114 by means of a connecting member 148 which supports the water seal 122 referred to above. The connecting member 148 allows the tank 112 to be located substantially vertically in the open position when the lower region of the tank bears against the stopper 140.

The tank 112 is designed to be buoyant in water when it is filled with air.

Accordingly, the tank 112 floats into the closed position, as illustrated in Figures 11, 13 and 15 of the accompanying drawings, when it contains a predetermined minimum volume of air. In this position, the buoyancy of the tank forces it against the stops 138 so as to hold the tank in the closed position.

When the level of the water in the reservoir reaches the entrance to the water inlet 124, it begins to flow through this inlet and into the tank 112 in the manner described above, and the two compartments 143A and 143B begin to fill up with water. An advantage of the baffle plate 143 is that it creates two separate air pockets within the tank 112 (one in each compartment of the tank). This modifies the position of the resultant buoyancy force acting on the tank so as to facilitate the relatively smooth pivoting of the tank into the open position.

As water flows into the ballast tank 112, air in the tank is expelled through the air line 130 and the volume of water in the tank, together with the mass of the tank, increases. As mentioned above, water which enters the air line 130 is drained from this line by the drain pipe 136, so as to prevent the development of a water seal within the air line.

When the mass of the tank 112 becomes sufficiently high, the tank begins to pivot about the hinges 116 towards the open position. The water inlet 124, the water outlet 128 and the air line 130 are all connected to the tank 112 by means of swivel couplings 150 which allow the tank to pivot relative to these members. As the tank pivots about the hinges 116, the counterweight 142 serves to facilitate the movement of the tank towards the open position.

Eventually, the tank 112 reaches the fully opened position where it contacts the stopper 140. In this position, a sealed chamber 152 is formed between the stopper 140, the tank 112, the member 148, the spillway 114 and the piers 118. Under normal conditions, the pressure developed in this chamber differs from the water pressure on the other side of the tank 112. This is due to the difference in the dynamic components of the various pressures as the water flows over the spillway 114, and tends to affect the movement of the tank relative to the spillway. The vent pipe 147 allows the fluid in the chamber 152 to communicate with ambient air, and accordingly prevents the development of excessive pressures within this chamber. In this way, the tank 112 can be maintained in the open position when high flow rates occur during flooding.

Initially, the head of water above the ballast tank 112 causes the water in the tank to flow through the water outlet 128A and out of the tank. As this water flows through the water outlet pipe 128, a siphon effect is developed in the pipe so that the water in the ballast tank 112 is sucked out of this tank As soon as the rate at which water is sucked out of the tank becomes greater than the rate at which water enters the tank, air is drawn into the tank via the air line 130. When this occurs, the buoyancy of the tank increases until it is sufficient to cause the tank to pivot upwards, towards the closed position. Once again, the counterweight 142 facilitates the smooth pivoting of the tank into the closed position so as to prevent shock loading as the tank contacts the stops 138.

In the closed position, the ballast tank 112 once again forms a barrier which projects above the crest of the spillway so that an additional quantity of water can be stored in the reservoir behind the spillway.

An advantage of the control gate of the embodiments of the invention described above is that it allows for additional water to be stored in a reservoir, and for the relatively rapid discharge of the additional water in the event that large quantities of water flow into the reservoir, such as during flooding.

Furthermore, the control gate of the invention can be controlled fully automatically.