WO2018154270A1

WO2018154270A1 - Apparatus and method for shielding a water intake on a waterway

Info

Publication number: WO2018154270A1
Application number: PCT/GB2018/050232
Authority: WO
Inventors: Ian Keith Taylor
Original assignee: Eco-Screen Limited
Priority date: 2017-02-22
Filing date: 2018-01-26
Publication date: 2018-08-30
Also published as: GB2559976B; GB201702870D0; GB2559976A

Abstract

An apparatus for shielding a water intake on a waterway comprises a screen (2) comprising a number of apertures or slots of width 3 mm or less, a support structure 4 for (5) supporting the screen in the waterway at an angle of inclination of 15º or less relative to a plane parallel to the water level of the waterway, a cleaning brush (20) for cleaning debris from the screen, and a drive mechanism (24, 26) for driving the cleaning brush across the screen. This approach provides an effective solution for excluding relatively weak swimming species such as elvers or lampreys from a water intake for an industrial installation, with improved cleaning and (10) less sheer forces on the waterway bed than existing screens.

Description

APPARATUS AND METHOD FOR SHIELDING A WATER INTAKE ON A WATERWAY

The present technique relates to an apparatus for shielding a water intake on a waterway.

Water may be drawn from a river or other waterway for a variety of industrial or agricultural purposes. For example, the water may be used by various industrial facilities such as hydroelectric power generators, steam electric power plants, oil refineries, chemical plants or public drinking water or sewage treatment plants, as well as for farm irrigation or other purposes. If fish enter the water intake then they may be killed or injured within the intake structures. This is a major problem especially for species which migrate up or down river for spawning, such as salmon, eel or lampreys, as any harm to young fish travelling up or down river may have a significant impact on fish populations. In addition to the environmental cost of any harm caused to the fish, there is also a financial cost to the operators of the facility using the water intake, as fish entering the water intake may cause damage to equipment such as turbines. Hence, a fish screen may be provided for shielding a water intake, to prevent fish from entering the water intake.

Some examples provide an apparatus for shielding a water intake on a waterway; comprising:

a screen comprising a plurality of apertures or slots of width 3 mm or less;

a support structure configured to support the screen in the waterway at an angle of inclination of 15^e or less relative to a plane parallel to the water level of the waterway;

a cleaning brush for cleaning debris from the screen; and

a drive mechanism configured to drive the cleaning brush across the screen.

Some examples provide a method for installing an apparatus for shielding a water intake on a waterway; comprising:

providing a screen comprising a plurality of apertures or slots of width 3 mm or less; supporting the screen in the waterway on a support structure with the screen at an angle of inclination of 15^e or less relative to a plane parallel to the water level of the waterway; and fitting a drive mechanism configured to drive a cleaning brush across the screen for cleaning debris from the screen.

Further aspects, features and advantages of the present technique will be apparent from the following description of examples, which is to be read in conjunction with the accompanying drawings, in which:

Figure 1 shows a side view of a fish screen supported at an angle of inclination of 15^e or less relative to the horizontal;

Figure 2 shows an example of a wedge-wire screen with a slot spacing of 3 mm or less;

Figure 3 illustrates a top view of the fish screen;

Figure 4 shows an example of a cleaning brush moving up or down the screen; Figure 5 shows an example of a control system for controlling operation of the screen; and

Figure 6 shows a method of controlling the cleaning operation of the screen.

In current fish screens, a mesh or grid is typically installed in the waterway at a relatively steep angle of elevation relative to the plane of the water level. The screen is typically oriented near to the vertical to reduce the lateral area required for installing the screen. Typically, the aperture size of the slots or apertures used for the screen is relatively large, for example 6 mm or greater.

However, some protected species such as elvers (baby eels) and lampreys are typically smaller than 6mm and so are not excluded by current screens. Providing a screen with a smaller aperture width has typically been regarded as impractical because with a smaller aperture size the apertures would more quickly be blocked by weeds, leaves, twigs or other debris washed down the waterway onto the screen, and so an effective solution for excluding elvers, lampreys or other relatively small aquatic species from industrial water intakes is not currently available.

The inventor recognised that these problems can be addressed for a screen with a smaller aperture size by orienting the screen at a shallower angle relative to the plane of the water level of the waterway. Hence, a screen with a number of apertures or slots of width 3 mm or less is provided with a support structure configured to support the screen at the waterway at an angle of inclination of 15^e or less relative to a plane parallel to the water level of the waterway. The shallower angle of inclination can be beneficial for screens with smaller apertures for a number of reasons.

With a shallower angle of inclination the debris passing down the river tends to be swept up the screen to the tide line at the surface of the water and so the portion of the screen below the surface tends to remain relatively clear decreasing the rate at which the screen becomes blinded with weeds or other debris. Hence, the shallower angle of that elevation helps to reduce the frequency at which the screen needs to be cleaned. Also, when the screen becomes partially or fully blocked, as the screen is oriented at a relatively shallow angle, the shear forces on the bed of the waterway are typically an order of magnitude lower than a screen erected at a steeper angle of inclination (with a steeper screen the component of the water flow perpendicular to the screen is greater which will tend to put more stress on the support structures for the screen). Therefore, with a shallower angle of inclination, the amount of civil engineering work required for providing concrete supports or other foundation structures for the screen can be reduced. In some cases the screen may not require any such in river works such as a temporary coffer dam, piling or concrete plinth construction. Another advantage of the shallow angle is that the screen can be fitted into areas where low water depth restricts the flow area. Also, the screen is less likely to impinge fish species which have a relatively weak maximum swimming speed. For example, lampreys have a particularly low maximum swimming velocity. Fish screens tend to trap species on the screen if the component of the water flow velocity which is perpendicular to the surface of the screen is greater than the maximum swimming speed of the species. By orienting the screen at a relatively shallow angle relative to the water level, the component of the water flow vector perpendicular to the screen is greatly reduced, and so relatively weak swimming species such as lampreys will be less likely to be entrapped on the surface of the screen and can more easily escape.

Hence, orienting the screen at a shallower angle of elevation relative to the plane parallel to the water level enables a small-aperture screen to be implemented in practice, providing an effective solution for protecting species such as lampreys and eels which are not well served by existing fish screens.

A cleaning brush is provided for cleaning debris from the screen, and a drive mechanism is provided to drive the cleaning brush across the screen. Hence, the screen can be cleaned of debris while remaining in situ, so that there is no need to remove the screen from the waterway in order to clean it. Unlike screens with larger aperture width, with a screen of aperture width 3 mm or less, the force required to remove debris from the screen is much lower as the force required for removal of debris tends to scale with the square of the cross-section size of the penetrating debris. Hence, with narrower apertures the cleaning mechanism does not need to generate a large force in order to remove debris from the screen. Therefore, rather than requiring a more complex mechanism where metal tines or prongs engage with each aperture of the screen and apply a larger force, a relatively simple cleaning brush passing over the screen can be enough to wipe debris from the screen. The relatively shallow angle of orientation of the screen means that it is feasible to use a brush cleaning mechanism because the weight of the brush will be substantially in a direction towards the screen rather than pulling the brush away from the screen as would be the case with a screen oriented more steeply relative to the waterway. By providing a cleaning mechanism which requires less force against the screen, the cleaning action applies lower shear forces to the banks or bed of the waterway than in current screens, and so the amount of engineering work for providing support for the screen to withstand the sheer forces can be reduced.

A debris trough may be provided positioned to collect debris brushed off the screen by the cleaning brush. As the screen is at a relatively shallow angle then fish or other species which approach the screen can pass over the screen into the debris trough. The debris trough may provide a bypass path for returning fish to the waterway, bypassing the water intake being shielded. The bypass flow may be via a sluice or weir for blocking debris and/or controlling the water flow. Clearing of debris from the debris trough could be performed manually when required, or could be automated with a further cleaning arm periodically sweeping the debris trough to remove debris into a separate debris trough not on the bypass path for fish to be redirected back into the waterway.

The cleaning brush may have flexible bristles, so that the brush action penetrates into the apertures at the surface of the screen, giving good removal properties for riparian debris. By using flexible bristles rather than rigid prongs or tines, the force on the screen and hence on the support structures can be reduced, allowing less expensive ground works to reduce the cost of installation of the screen. The brush may be removable and replaceable. The cleaning brush may be mounted on an arm which passes across the screen and is driven up and down the screen by the drive mechanism.

The drive mechanism may comprise a pair of toothed drive belts which carry the cleaning brush across the screen, and at least one motor for driving the toothed drive belts. The drive mechanism may use a direct drive mechanism, so that the motor drives the belts and the belts carry the brush without an intervening clutch mechanism for changing gearing. A direct drive mechanism can be useful for allowing displacement of the brush to be detected based on the number of rotations of the motor, which can be useful for control of the cleaning cycles as described below. By using toothed drive belts to carry the brush, there is no need for lubrication which would otherwise be required with alternatives such as using a drive chain. This can be particularly useful in situations where contamination of the water being passed through the screen is undesirable, such as for hydroelectric power applications where the water extracted is passed through a turbine and then returned to the waterway without treatment (for other applications such as sewage treatment works the water may already be treated to make it safe for return to the waterway and so it may not be a problem to use a drive chain with lubrication, so a drive chain could still be used for such applications).

The drive mechanism may apply a force to the cleaning brush in a direction parallel to the plane of the screen (e.g the direction parallel to the slots of the screen). For example the toothed drive belt may be mounted parallel to the screen and the drive may wind the drive belts around a looped path so that the drive belts pull the cleaning brush in a direction parallel to the screen. There is no need for the drive mechanism to apply any force perpendicular to the screen as the force maintaining the cleaning brush in contact with the screen may be provided by the weight of the cleaning brush itself.

At least one sensor may be provided to sense at least one operating parameter of the fish screen, and the drive mechanism may have a controller which automatically triggers a cleaning cycle for cleaning the screen using the cleaning brush in response to detecting that the at least one operating parameter meets a cleaning trigger condition. For example, one cleaning cycle may correspond to the brush being driven from one side of the screen to the side at which the debris trough is located, and then after a period of rest being returned back to its original starting position. Hence, the intervention of a human operator is not required for cleaning as the controller may automatically trigger cleaning when certain operating conditions of the screen are detected. It will be appreciated that the system may also allow a human operator to trigger a cleaning cycle manually when desired, even if the automatic control has not sensed a relevant operating condition for triggering cleaning.

For example, one way of sensing the cleaning trigger condition may be to provide water level sensors for sensing the water levels upstream and downstream of the screen, and to trigger the cleaning cycle when it is detected that a difference between an upstream water level and a downstream water level (or "head loss") is greater than a predetermined threshold. When the downstream water level beyond the screen becomes significantly lower than the upstream water level then this may be an indication that the screen is getting blocked by debris and so is backing up behind the screen, and so a cleaning cycle is triggered to remove the debris. Cleaning cycles could also be triggered by other events. For example, the cleaning cycle could be triggered periodically on elapse of a certain amount of time since a previous cleaning cycle.

Unlike screens oriented at a steeper angle relative to the waterway, with a shallow angle of inclination, there is a greater risk that relatively large objects such as tree branches may wash down river and remain resting on the screen. In this case, when the cleaning brush is driven across the screen, it may hit the obstruction and become jammed. The system may be provided with a controller which detects an obstruction condition when the cleaning brush is obstructed from passing across the screen, and triggers an obstruction handling response when the obstruction condition is detected. There may be a number of ways in which the obstruction condition can be detected.

In one example, the obstruction condition can be detected based on the motor current of a motor used in the drive mechanism. When an electric motor is prevented from rotating then it draws a high amount of current typically referred to as a stall current. Hence, when the cleaning brush hits an obstruction such as a branch, this stops the motor rotating causing a current spike, which can be detected by comparing the motor current with a given threshold.

Another technique for detecting the obstruction condition may be to sense the displacement of the cleaning brush on either side of the screen. For example there may be a first drive element on one side of the cleaning brush and a second drive element on the other side of the brush, for carrying the respective ends of the brush across the screen. For example the first and second drive elements may be toothed drive belts as discussed above. If the obstruction is closer to one side of the screen than the other, one of the first/second drive elements may jam up more than the other, causing the drive element on the other side to carry the brush further than the drive element on the side nearest the obstruction. Hence, the obstruction can be detected when the difference between the displacement of the first drive element and the displacement of the second drive element is greater than a threshold. The displacement of the drive elements can be detected directly from the number of rotations of the motor when a direct drive mechanism without variable gearing is used, such as where the motor directly drives a toothed drive belt. Alternatively, a displacement sensor (separate from the motor) could be used.

In some systems, only one of these techniques for detecting the obstruction condition could be used. Alternatively, both detection techniques could be implemented in the same apparatus, so that the obstruction handling response is triggered in response to either a high motor current or a large difference between the brush displacement on either side of the screen.

The obstruction handling response triggered when the obstruction is detected may vary from system to system or can include several responses. For example the obstruction handling response may comprise at least one of: suspending or restarting a cleaning cycle using the cleaning brush, reversing a direction of travel of the cleaning brush across the screen, and signalling the obstruction condition to a control centre or operator. In some cases, the obstruction handling response could first attempt to restart the cleaning cycle, but if this is not successful for a given number of times then the obstruction condition could be signalled to a control centre or operator to prompt a human operator to resolve the obstruction. For example, it may be that if the direction of travel is reversed and the cleaning brush is returned to its previous resting position then the next time a cleaning cycle is restarted the obstruction may already have moved, and so sometimes simply suspending and then restarting the cleaning cycle can be enough. Other times this may not be successful and so after a given number of retries the screen can send a signal to a control centre or an operator to inform them that an obstruction has occurred, and then a human operator can step in and remove the obstruction. The signal sent to the control centre or human operator could be an audible alarm, a flashing light, or a signal sent by wireless communication such as a radio signal, for example.

The apertures or slots in the screen can be of a variety of shapes or arrangements. For example the screen could comprise holes of maximum diameter 3 mm or less, or slots where in one dimension the width is less than or equal to 3 mm to prevent the passage of aquatic species, but in another dimension the slots may be wider.

In one example the screen may comprise a wedge-wire screen. Hence the screen comprises a number of wires running parallel to each another with slots between the wires. The wire cross section may form a wedge shape, so that it is wider at one side than the other. The wider side of the wires may be at the surface presented to the oncoming water flow, and the spacing between the wires at that surface may be 3 mm or less (even if the spacing between the wires on the opposite surface of the screen is greater than 3 mm). A wedge-wire screen can be robust, strong, relatively cost effective to manufacture and can easily be manufactured with a range of aperture spacings and so can provide an effective screen for shielding the water intake from fish. The slots formed between the wires forming the wedge-wire screen may run parallel to a direction of travel of the cleaning brush when driven by the drive mechanism. This improves the cleaning properties of the brush since the brush bristles can then run along the slots of the screen in order to remove weeds and other debris. When installed on the waterway, the screen may be installed with the slots running parallel to the water flow direction.

The screen may have an aperture width of 3 mm or less. More particularly, the apertures or slots the screen may have a width of 2 mm or less, which can be particularly useful for excluding elvers or lampreys.

Although the angle of inclination may in general be 15^e or less, it has been found that it is particularly useful for the angle of inclination to the 10^e or less which provides a further reduction in the forces of the riverbed and the swimming velocity which is required to escape the screen as discussed above. In some cases the angle of inclination may be horizontal (0^e). In this case the water intake from which water is drawn from the waterway may be below the screen (e.g. installed within the bed of the waterway). However, it many cases it can be useful to provide at least some angle of inclination relative to the waterway in order to increase the area presented to the flow direction and so it may be useful for the angle of inclination to be greater than 0^e. When the angle of inclination is greater than 0^e, the drive mechanism may drive the cleaning brush to travel from the bottom of the incline towards the top of the incline to brush debris off the screen and into a debris trough positioned at the top of the incline. When installed on the waterway, the screen can be installed with the top of the incline downstream from the bottom of the incline.

Figure 1 shows an example of an apparatus for shielding a water intake on a waterway. For example the waterway can be a river, estuary, canal, stream, or any other body of water, including the open sea. As shown in Figure 1 the apparatus comprises a screen 2 which is supported within the waterway by a support structure 4. The support structure 4 in this example includes a support post and a cross beam which are arranged to support the screen 2 in the waterway at an angle of inclination of 15^e or less relative to a plane parallel to the water level of the waterway. The plane parallel to the water level (the surface of the water) is referred to as the horizontal. The screen may operates at a relatively low specific flowrates per unit area. For example, the specific flowrate may be less than 100 litres per m² screen area per second. This has several benefits, as the typical head loss across a clean screen is less than 10mm, the "attractive" forces generated by the flow through the screen are low (these are the forces which can trap weak swimming species against the surface of the screen). Due to the low angle of screen inclination the sweeping horizontal flow will tend to push any weak swimming species to the debris trough and bypass exit. Also, drag forces opposing the downwards motion of the brush wiper arm are low.

As shown in Figure 2, the screen 2 comprises a wedge-wire screen which includes a number of wedge-shaped wires 6 mounted on cross beams 8. Each wire has a wedge-shaped cross section with the wider part of the wedge at the top surface of the screen and the narrower part of the wedge connected to the cross beams 8. Neighbouring wires 6 are separated by a slot spacing of 3 mm or less at the top surface of the screen. In other embodiments the aperture spacing of the screen may be smaller for example 2 mm or less, and can be as small as 0.5 mm. While Figure 2 shows an example where the screen includes a number of slot- shaped apertures, other examples may have different shaped apertures, for example round or square holes between the cross members of a mesh or grid pattern, or apertures of a more arbitrary shape, with the apertures having a dimension in at least one direction which is 3 mm or smaller to prevent passage of fish species larger than 3 mm.

Returning to Figure 1 , a debris trough 10 is positioned at the downstream side of the screen at the top of the incline. Fish and debris (e.g. leaves, weeds or litter) washed down the waterway onto the screen tend to be washed up the screen by the water flow and into the debris trough. Figure 3 shows a top view of the screen installed in the waterway and shows that the debris trough provides a bypass flow whereby fish or invertebrates and the debris can be directed via a sluice or weir back into the waterway. Water may periodically be passed through the debris trough to wash remaining debris away. Meanwhile, the filtered water which passes through the screen flows from beneath the debris trough and can then be tapped off by a water intake positioned behind the screen for use in industrial or agricultural equipment. A range of equipment options are available for the management of debris collected in the debris trough, ranging from fully automated debris transfer to manual removal/disposal. The preferred debris handling system may depend on the screen size and flowrate, type and quantity of expected river debris, and type of installation (e.g. whether the screen is a brand new installation or a retrofit into an existing trash rack slot, whether the premises are remote or manned, etc.).

As shown in Figures 1 and 3, a cleaning brush 20 is provided on an arm mounted between a pair of drive elements 22 positioned on either side of the screen. As shown in Figure 1 , each drive element 22 comprises a toothed drive belt 24 which is driven by a corresponding motor 26 (although Figure 1 shows a side view and so shows only a single motor, there may be separate motors provided on either side of the screen to drive each of the pair of drive belts). As shown in Figure 3, the slots in the screen 2 may be oriented parallel to the water flow and parallel to the drive direction of the wiper brush 20. Hence, as shown in Figure 4, the motor 26 may drive the toothed drive belt 24 to carry the brush up and down the screen. The wiper brush 20 may be supported between the drive belts and held in place solely by the tension in the drive belts, without needing any other fixing in order to fix the brush to the drive belt. As the angle of elevation of the screen relative to the horizontal is relatively shallow, the weight of the brush is near perpendicular to the screen and so holds the brush against the screen so that there is no need for drive mechanism to provide any force perpendicular to the screen. Instead the drive belts 24 simply apply a force parallel to the plane of the screen and the weight of the brush ensures that the flexible bristles of the brush penetrate into the slots in the screen. As the slots run parallel to the direction travel of the brush, the bristles travel along the length of the slots to extract weeds or other debris from between the wires, and brush the debris in to the debris trough. A bywash mechanism may be provided to flow water through the debris trough in order to wash the debris through the sluice or weir back in to the waterway. The brush cleaning system may operate at a relatively low speed, e.g. typically less than 100 mm/second. Due to its action on the low inclination screen much lower forces are generated during the cleaning operation than existing design screens. This also reduces the support structure costs that are required to resist these forces.

As shown in Figure 5, the screen is provided with a control system 30 which comprises a controller 32 (e.g. a microcontroller or other relatively low power processing unit) and a number of sensors for sensing operating conditions of the screen. The controller 32 could be provided within the housing of one of the motors 26 or in a separate unit. The sensors may include water level sensors 34, 36 for sensing the height of the water level above the bed of the waterway at positions upstream and downstream of the screen, as well as sensors within the motors 26 which sense the current drawn by the motors, or the number of rotations of the motors which provides a measure of displacement of the cleaning brush on either side of the screen. The control system 30 is also provided with a communications circuit 38 which may be provided with an antenna 40 for transmitting or receiving radio signals. Hence, warning signals can be transmitted to external control systems in order to draw the attention of a human operator for example. Although not shown in Figure 5, the system may also include various cameras which may capture images of the screen in operation which can be beamed back to the control centre, so that a human operator can observe the screen from a remote location and then trigger a repair or maintenance action if necessary. Hence, there is no need for a human operator on site. The upstream and downstream water levels monitored by sensors 34, 36 can be compared and if the difference is greater than a certain threshold then this may trigger a cleaning cycle.

The control system 30 also includes proximity sensors 37 for sensing when the cleaning brush 20 has reached the top or bottom of the screen during its cleaning cycle. Four sensors 37 are provided, a pair of sensors at the bottom of the screen (one on each side of the brush to track the progress of the drive mechanism on each side of the brush), and another pair at the top of the screen. For example, each proximity sensor 37 may comprise a Reed switch which detects when a magnet attached to the drive belt or on end of the cleaning brush is closer to the switch than a certain distance. It will be appreciated that other types of proximity sensor could also be used. The displacement indication provided by the motor 26 tends to drift from the actual brush displacement over time, so the proximity sensors 37 are provided to sense when the brush has reached the top or bottom of the screen. When the controller 32 detects that the brush has reached the top or bottom of the screen on one side or other, the controller 32 controls the corresponding motor to stop driving the brush up or down the screen, and also resets a counter which tracks the number of rotations of the motor.

The control system 30 determines the cleaning intervals which are dependent on the river conditions. In river sensors 34, 36 monitor the head loss across the screen and activate a cleaning cycle when the head loss (difference between upstream and downstream water levels) is less than a threshold. For example, a typical value for head loss triggering a cleaning cycle may be 75 mm. A cleaning cycle starts with the brush wiper arm 20 moving from its normal position at the low end of the screen. The brush 20 travels the full length of the screen pushing any debris present into the debris trough 10. After a pause time (e.g. 10 seconds), the brush 20 returns to the lower end of the screen to await the next cleaning cycle. Sensors attached to the toothed belt drive motors 26 measure the individual rotations of the drives. Using this information the control system can determine if there is any "exceptional" resistance to movement. This may occur if exceptional size debris e.g. a large branch fouls the screen. The obstruction can be detected either based on the motor current exceeding a threshold or based on the difference in displacement on either side of the brush wiper arm 20 being greater than a threshold. When the obstruction is detected, the control system 30 stops the drive of the brush wiper arm 20, reverses the direction of travel back to its last halt position (top or bottom of screen) and then starts the cleaning cycle again. The cleaning cycle will be restarted, and if the fault conditions again occur, the cleaning operation is halted and an alarm for operator attention is sent.

Figure 6 is a flow diagram showing a method of operating the screen. At step 100 the controller 32 determines whether a cleaning trigger condition has been detected. For example the cleaning trigger condition could be the head loss being greater than a certain threshold as discussed above but could also be other events such as the elapse of a given amount of time since the last cleaning cycle, or a human operating manually triggering a cleaning cycle. When a cleaning trigger condition is detected, at step 102 a cleaning cycle is started and the brush 20 is driven from its normal resting position at the bottom of the incline, up the screen with its flexible bristles passing in through the slots in the screen to brush debris out. At step 104 the controller detects whether an obstruction condition has been detected. If no obstruction is detected, the cleaning cycle continues and once the cleaning cycle is finished and the brush has reached the top of the screen and then passed back down again to the bottom, the method returns to step 100 to check for another cleaning trigger condition when a subsequent cleaning cycle is required.

However, if an obstruction condition is detected at step 104, e.g. based on the current drawn by the motor or the difference in displacement of the brush on either side of the screen, then at step 106 the controller detects whether the number of retries is greater than a certain threshold. If not, then at step 108 the brush is rewound to its last resting position (to the bottom of the screen if the brush is currently travelling up the screen, or to the top of the screen if the brush is currently travelling down the screen). When the brush has rewound to the last resting position then it remains there for a certain period and then resumes the cleaning cycle, and if the obstruction is no longer present the cleaning cycle may then complete. The method returns to step 104 to check whether the obstruction is detected again, and if not then the method returns to step 100 as the cleaning cycle has been successful. However, if at step 106 the number of retries becomes greater than a certain threshold then it may be detected that the obstruction is not being removed by the action of the water flow itself, and so a human operator may need to step in to remove it. Hence, at step 1 10 the controller 32 controls the communication circuitry 38 to signal the obstruction to a human operator or a control centre.

In the present application, the words "configured to..." are used to mean that an element of an apparatus has a configuration able to carry out the defined operation. In this context, a "configuration" means an arrangement or manner of interconnection of hardware or software. For example, the apparatus may have dedicated hardware which provides the defined operation, or a processor or other processing device may be programmed to perform the function. "Configured to" does not imply that the apparatus element needs to be changed in any way in order to provide the defined operation.

Although illustrative embodiments of the invention have been described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope and spirit of the invention as defined by the appended claims.

Claims

1 . An apparatus for shielding a water intake on a waterway; comprising:

a screen comprising a plurality of apertures or slots of width 3 mm or less;

a cleaning brush for cleaning debris from the screen; and

a drive mechanism configured to drive the cleaning brush across the screen.

2. The apparatus according to claim 1 , comprising a debris trough positioned to collect debris brushed off the screen by the cleaning brush.

3. The apparatus according to claim 2, wherein the debris trough provides a bypass path for returning fish to the waterway bypassing the water intake.

4. The apparatus according to any preceding claim, wherein the cleaning brush has flexible bristles.

5. The apparatus according to any preceding claim, wherein the drive mechanism comprises a pair of toothed drive belts configured to carry the cleaning brush across the screen, and at least one motor configured to drive the toothed drive belts.

6. The apparatus according to any preceding claim, wherein the drive mechanism is configured to apply a force to the cleaning brush in a direction parallel to the screen.

7. The apparatus according to any preceding claim, wherein a force maintaining the cleaning brush in contact with the screen is provided by the weight of the cleaning brush.

8. The apparatus according to any preceding claim, comprising at least one sensor to sense at least one operating parameter of the fish screen;

wherein the drive mechanism comprises a controller configured to automatically trigger a cleaning cycle for cleaning the screen using the cleaning brush in response to detecting that the at least one operating parameter meets a cleaning trigger condition.

9. The apparatus according to claim 8, wherein said at least one sensor is configured to sense water levels upstream and downstream of the screen; and

the predetermined operating condition comprises a difference between an upstream water level and a downstream water level being greater than a predetermined threshold.

10. The apparatus according to any preceding claim, wherein the drive mechanism comprises a controller configured to detect an obstruction condition when the cleaning brush is obstructed from passing across the screen, and in response to detecting the obstruction condition, to trigger an obstruction handling response.

1 1 . The apparatus according to claim 10, wherein the drive mechanism comprises at least one motor, and the controller is configured to detect the obstruction condition when a motor current of the at least one motor is greater than a threshold.

12. The apparatus according to any of claims 10 and 1 1 , wherein the drive mechanism comprises a first drive element configured to carry one side of the cleaning brush and a second drive element configured to carry the other side of the cleaning brush; and

the controller is configured to detect the obstruction condition when difference between a displacement of the first drive element and a displacement of the second drive element is greater than a threshold.

13. The apparatus according to any of claims 10 to 12, wherein the obstruction handling response comprises at least one of:

suspending or restarting a cleaning cycle using the cleaning brush;

reversing a direction of travel of the cleaning brush across the screen; and

signalling the obstruction condition to a control centre or operator.

14. The apparatus according to any preceding claim, wherein the screen comprises a wedge-wire screen.

15. The apparatus according to claim 14, wherein slots formed by the wedge-wire screen run parallel to a direction of travel of the cleaning brush when driven by the drive mechanism.

16. The apparatus according to any preceding claim, wherein the apertures or slots of the screen have a width of 2 mm or less.

17. The apparatus according to any preceding claim, wherein the angle of inclination is 10^e or less.

18. The apparatus according to any preceding claim, wherein the angle of inclination is greater than 0^e.

19. The apparatus according to claim 18, wherein the drive mechanism is configured to drive the cleaning brush to travel from the bottom of the incline towards the top of the incline to brush debris off the screen into a debris trough positioned at the top of the incline.

20. A method for installing an apparatus for shielding a water intake on a waterway; comprising:

21 . The method of claim 20, wherein the angle of inclination is greater than 0^e, and the screen is installed on the waterway with the top of the incline downstream from the bottom of the incline.