Crest gates for controlling the water level upstream of a spillway are known.

Generally, these gates increase the height of the spillway so that an additional quantity of water can be stored in a reservoir upstream of the spillway, and at the same time are arranged to allow the additional water to be discharged from the reservoir in the event of a flood.

A problem associated with many conventional crest gates is that they are not fully automatic, and consequently have to be controlled manually or electrically.

Although automatic crest gates are also known, many of these gates include ballast tanks or the like and often are relatively complex in construction. A further drawback associated with conventional automatic crest gates is that they tend to be bulky and are not always easy to connect to existing spillways.

Furthermore, once connected to an existing spillway, many of these crest gates have adverse influences on the stability of the spillway.

For the purpose of this specification, the phrase"added live water storage height"refers to the difference in height between the highest point on a water control gate when the gate is closed and the highest point on the water control gate when the gate is open; the term"downstream"refers to the direction in which water flows over a spillway; and the term"upstream"refers to the opposite direction.

SUMMARY OF THE INVENTION According to the invention there is provided a water control gate in the form of a movable barrier which is connected or connectable to a spillway by means of a pivot arrangement 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; the movable barrier defining a curve which is convex when viewed from the upstream side of the barrier, which extends over at least a substantial portion of the barrier and which has at least one radius of curvature which is between 50% and 150% of the added live water storage height; the movable barrier being arranged to extend upwardly from the pivot arrangement in use so that, in the closed position, an upper region of the movable barrier is spaced downstream from a pivot axis defined by the pivot arrangement and at least a portion of the curve on the movable barrier is spaced upstream from the pivot axis by a distance of at least 15% of the added live water storage height; and the water control gate including a counterweight for biasing the movable barrier into the closed position.

In a preferred embodiment of the invention, the radius of curvature of the convex curve on the movable barrier is substantially the same as the added live water storage height.

Typically, the movable barrier defines a cylindrical or part-cylindrical surface at a lower region thereof which extends at least partially around the pivot axis of the pivot arrangement. In this case, the radius of curvature of the cylindrical or part-cylindrical surface may be between 20% and 30% of the added live water storage height, and is preferably approximately 24% of the added live water storage height.

The counterweight may comprise a concrete and/or steel mass which is attached to the movable barrier by means of a lever.

In one embodiment, the lever is fixed to the barrier at one end and is hingedly connected to the counterweight at the other end.

In a preferred form of the invention, the movable barrier includes a steel loading face for receiving loads from water in a reservoir upstream of the barrier, and a series of spaced-apart gussets are provided on the downstream side of the barrier for strengthening the loading face.

Preferably, a water seal is provided between the movable barrier and the spillway for preventing water from flowing under the movable barrier and over the spillway.

In one arrangement, the water seal is in the form of a music-note seal which is arranged to bear against the lower region of the movable barrier.

Typically, the water control gate also includes water seals between the sides of the movable barrier and side piers for preventing water from flowing past the sides of the movable barrier and over the spillway.

The spillway and/or the side piers may include an air duct for allowing air to be drawn into a low pressure region on the downstream side of the movable barrier when the barrier is at least partially open and water flows over the barrier.

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 view from the upstream side of a water control gate according to the present invention mounted on a spillway in a closed condition; Figure 2 shows, diagrammatically, a cross-sectional view along the line 2-2 in Figure 1; Figures 3 and 4 show, diagrammatically, cross-sectional views similar to that of Figure 2 with the control gate in a partially open condition and a fully open condition, respectively; and Figures 5 to 8 show, diagrammatically, cross-sectional views similar to that of Figure 2 of other, further embodiments of the control gate according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Figures 1 to 4 of the drawings illustrate a water control gate 10 according to the present invention. As can be seen, the gate 10 includes a movable barrier 12 which is connected to the top of a spillway 14 by means of a plurality of hinges 16. The hinges 16 are connected to the spillway by means of support brackets 18 (see Figures 2 to 4), and are arranged to extend longitudinally across the spillway so as to provide a substantially horizontal pivot axis 20 about which the barrier 12 can pivot.

The movable barrier has a mild steel loading face 22 for receiving loads from water in a reservoir 24 on the upstream side of the barrier and is seen to include a plurality of spaced-apart, steel gussets 26 on the downstream side of the loading face. A portion of the face 22 defines a curve 28 which is convex when viewed from the upstream side of the movable barrier 12, as illustrated.

In this embodiment of the invention, the curve 28 extends from a steel cylinder 30 at the base of the movable barrier to a lip 32 at the free end 34 of the barrier. The specific shape of the loading face 22 is an important feature of the invention and is described in more detail below.

The steel cylinder 30 is fixed to the hinges 16 so as to allow the barrier 12 to pivot over the top of the spillway between a closed position, as illustrated in Figure 2 of the drawings, and an open position as illustrated in Figure 4.

Below the steel cylinder 30, a water seal designated generally with the reference numeral 36 extends along the length of the spillway 14 to prevent water from flowing under the movable barrier and over the spillway. The water seal 36 in the illustrated embodiment is a music-note seal 38 which is carried at one end of a stationary steel barrier 40 extending along the length of the spillway 14, as shown.

A counterweight in the form of a steel mass 42 is connected to the loading face 22 of the movable barrier by means of a lever 44 which is welded to the loading face at one end 46 and hingedly connected to the steel mass 42 at the other end 48.

With particular reference now to Figure 1 of the accompanying drawings, the movable barrier 12 is located between a pair of piers 50. In practice, there may be a series of gates 10 extending along the top of a spillway with a plurality of piers separating the gates from one another. In Figure 1, one of the piers 50 is seen to include an air duct 52 for allowing air to flow to the downstream side of the movable barrier 12 when the gate is open, and the barrier 12 is seen to be separated from the piers 50 by water seals 54 which prevent water from flowing between the barrier and the piers, and over the spillway 14. Adjacent the steel barrier 40 the spillway 14 defines a water drain pipe 56 (see Figures 2 to 4) for draining water from a channel 58 on the downstream side of the music-note seal 38.

If desired, the counterweight may be designed so as to be adjustable either by increasing or decreasing the mass thereof or by changing the position of the counterweight on the lever 44.

In use, the water control gate 10 is connected to the spillway 14 in the manner illustrated in Figure 2. If necessary, the counterweight is adjusted so that the gate is correctly set, as required. The movable barrier 12 is illustrated in a closed position in Figure 2 in which the height of the spillway is effectively increased by the distance from the crest of the spillway 60 to the free end 34 of the loading face 22. With the control gate in this position, the water level in the reservoir 24 is allowed to rise above the crest of the spillway 14, as shown, and the water storage capacity of the reservoir is substantially increased.

The counterweight 42 retains the gate 10 in the closed condition as the water level in the reservoir 24 rises above the free end of the loading face 22 so that the water initially flows over the edge of the loading face as if over a sharp- crested weir. It will be appreciated that the water flowing over the edge of the loading face is directed onto the spillway so as to flow over the spillway and away from the movable barrier 12.

As the level of the water rises, the resultant horizontal load applied to the loading face 22 by the water pressure in the reservoir increases until this resultant load is sufficient to cause the movable barrier 12 to pivot about the pivot axis 20 towards the open position against the bias of the counterweight.

The geometry of the control gate 10 is such that once the level of the water in the reservoir rises above a predetermined level, a relatively small increase in the water level results in a corresponding small pivotal displacement of the barrier 12 towards the open position. If the water level then subsides, the counterweight will draw the barrier 12 back into the closed position. However, if the water level continues to rise, the barrier 12 will continue to pivot gradually towards the open position. The water control gate 10 is illustrated in a partially open condition in Figure 3 and in a fully open condition in Figure 4.

When the water level in the reservoir 24 rises suddenly, such as during a flood, the gate 10 is designed to pivot into the open condition relatively quickly so as to allow the excess water in the reservoir to be discharged as quickly as possible.

As the gate pivots towards the open condition, the air duct 52 allows the downstream side of the movable barrier 12 to remain in communication with ambient air so as to prevent the development of sub-atmospheric pressures on this side of the gate as the water flows over the movable barrier. In Figures 2 to 4, the surface of the cylinder 30 can be seen to maintain contact with the music-note seal 38 as the barrier 12 rotates between the closed and the open positions, thereby preserving the water seal at the base of the barrier 12. The surface of the cylinder 30 also allows for stable flow of water over the movable barrier 12, even when the barrier is in the fully open position.

When the level of the water in the reservoir 24 drops again, the counterweight draws the gate 10 back into the closed condition, in a similar fashion to that described above with reference to the opening of the gate. It will be appreciated that hydrodynamic forces in the water flowing over the movable barrier reduce the hydrostatic forces applied to the loading face 22, and this assists the counterweight in biasing the movable barrier back into the closed position.

In order to effect the gradual opening and closing of the gate 10, it has been found that the radius of curvature of the convex curve 28 on the loading face 22 should be approximately equal to the added live water storage height, as defined above. This curvature corresponds generally to the profile of the underside of a body of water flowing over a sharp-crested weir when the difference in height between the top of the weir and the water level in the reservoir behind the weir is approximately equal to the added live water storage height associated with the gate 10. Also, the distance between the surface of the cylinder 30 and the pivot axis 20 of the hinges 16 should be approximately 24% of the added live water storage height.

Figures 5 to 7 illustrate other, further embodiments of the water control gate according to the present invention. The control gates here are similar in many respects to the control gate 10 described above, but in each case, the free end 110,210 and 310 of the loading face 112,212 and 312 is formed differently to that of the water control gate illustrated in Figures 1 to 4 of the drawings. As can be seen, the free end of the loading face of the gate illustrated in Figure 5 is curved upwardly, the free end of the loading face of the gate illustrated in Figure 6 is substantially straight, and the free end of the loading face of the gate illustrated in Figure 7 is initially straight and then curves downwardly. In practice, the shape of the free end of the loading face will be varied according to specific design considerations. However, in each case, the loading face will include a convex curve 128,228 and 328, as illustrated.

As in the case of the water control gate 10, the geometry of the gates illustrated in Figures 5 to 7 is such that the gates open and close gradually as the water level in the reservoirs upstream of the spillways rises and falls, respectively.

Figure 8 illustrates yet a further embodiment of the control gate according to the present invention. In this case, a movable barrier 412 is connected to a spillway 414 by means of an integral pivot arrangement and water seal 416, as illustrated. A counterweight 418 is connected to the barrier 412 by means of a lever 420 in a similar fashion to that of the control gates illustrated in Figures 1 to 7. Also similarly to the previous embodiments, the barrier 412 includes a convex curve 422 which is specifically designed to allow the gate to gradually open or close as the water level in a reservoir 424 behind the spillway 414 rises or falls, respectively.

An advantage of the water control gate of each of the embodiments of the invention described above is that the gate operates automatically to store additional water in a reservoir and to control the release of excess water when the water level in the reservoir rises above a predetermined level. In particular, the water control gate is arranged to open and close gradually with relatively small changes in water level above the predetermined level so that excess water can be discharged from the reservoir at different rates, depending on the rate at which water is entering the reservoir. Also, the gate is of a relatively simple construction, and can be fitted to existing spillways relatively easily.

Although the water control gate of the invention has been described with reference to a reservoir spillway, it should be clear that the gate is not limited to such use and may also be used in other suitable applications such as, for example, for regulating water levels in water treatment works and irrigation canals, on weirs and in tidal basins.