US20030095837A1

US20030095837A1 - Method of carrying out, and apparatus for use in, flood irrigation

Info

Publication number: US20030095837A1
Application number: US10/298,791
Authority: US
Inventors: Nicolaas Sieling
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-11-19
Filing date: 2002-11-19
Publication date: 2003-05-22
Also published as: AUPR895701A0

Abstract

An apparatus and a method for irrigating land are disclosed. The apparatus comprises a portable sensing device that is anchored at a chosen locality in the land, gripping one end of a control line such as a length of twine. The control line is connected to a flow control mechanism that controls the operation of a mechanism such as a gate through which water flows from an irrigation canal to the land. The sensing device holds the control line under tension. The sensing device is provided with means, such as a float, to detect the arrival of water flowing onto the land and, in response, releases the control line. This actuates the flow control mechanism to close the gate.

Description

FIELD AND BACKGROUND OF THE INVENTION

This invention relates to a method of carrying out flood irrigation and apparatus for use therein.

In one known method of flood irrigation, a bank is provided along a canal bordering the land to be irrigated. The bank may be natural but would more usually be man made. The bank enables the level of water in the canal to be raised above the level of the land. A number of breaches are formed at intervals along the bank A delivery mechanism called a ‘gate’ is placed in each breach for controlling the flow of water therethrough onto the land. The land is divided into sections, called ‘bays’, each of which is served by one or more of the gates.

The method works best with land that is levelled and that slopes gently downwardly away from the bank at a predetermined angle. In this way, water that enters a bay through a gate at the upper end of the bay flows towards the lower end, thus covering the entire bay. For various reasons that need not be discussed here, it is common practice to allow water from the canal to flow onto only one, or at least a limited number, of the bays at one time. This is achieved by opening only those gates that serve the selected bays, the gates to the remainder of the bays being closed.

It is considered bad practice to over-water the land and the water flowing into a bay is cut off as soon as the bay has received enough water. Typically, a bay may be watered for about four hours. Operators commonly work to a timetable when watering and, because the process is often not automated, they must return to the land every four hours (in this example) around the clock to close the gates to one bay and open the gates to another bay.

PRIOR ART

Various systems have been devised in attempts to facilitate and improve this process. Mechanisms have been proposed that automatically open and close the gates. In some cases the mechanisms are controlled by timing devices or devices that measure the volume of water which flows through the gate. One disadvantage of the use of such devices is that the amount of water that is actually delivered to a bay is at best an estimate and is not necessarily the optimum amount of water that the bay needs at that particular watering. In other cases, the mechanisms are controlled by sensors located at or near the lower ends of the bays. The sensors, upon sensing the arrival of the water, send signals that cause the gates to be opened and/or closed as required. The applicant knows of two of such systems. In one these systems, in which the signal is a radio signal, the sensor can readily be moved from one position to another in a bay. However, this system is expensive. In another system, the sensor is connected to an operating mechanism that operates the gate by means of a small diameter hose. Water arriving at the sensor fills a receiver connected to the hose. The air displaced from the receiver by the water is pumped along the hose. The operating mechanism is triggered into action by the air flowing through the hose. These installations cannot be readily moved. In particular, the sensors and hoses are left in place on the land once they have been installed. STATEMENTS OF INVENTION

In one aspect of the invention, apparatus for use in irrigating land comprises an anchoring device arranged to anchor a control line under tension in the land, means to detect a change in wetness in the land and means to cause the anchoring device to change the tension in the control line in response to a change in such wetness.

In one form of the invention, the means to detect the change in wetness comprises means to detect an increase in water level at a chosen locality in the land.

In one form of the invention the means to detect the increase in water level comprises a float, the apparatus comprising means to connect the float to the anchoring device in such manner as to cause the anchoring device to change the tension in the control line when the float rises with a rise in the water level.

In an alternative form of the invention support means is provided for supporting at least a portion of the anchoring device above the land, the support means being arranged to sink into the land when the land softens as a result of an increase in wetness in the land. Advantageously the support means comprises at least one member having a pointed end that is arranged to sink into the land when the land softens.

In one form of the invention the means to cause the anchoring device to change the tension in the control line comprises means to grip the control line and to release the control line in response to a change in wetness in the land.

According to one aspect of the invention the means to grip the control line comprises a spring, the apparatus comprising means for putting the spring under load when the control line is to be gripped, and to release the load in response to a change in wetness in the land.

Further according to the invention, apparatus for use in irrigating land comprises delivery means for delivering water to the land, a flow control mechanism movable between first and second operating positions in one of which the flow control mechanism allows water to flow through the delivery means and in the other of which the flow control mechanism prevents the flow of water through the delivery means, an anchoring device arranged to anchor a control line connected under tension to the flow control mechanism, means to detect a change in wetness in the land and means to cause the anchoring device to change the tension in the control line in response to a change in such wetness, the flow control mechanism being arranged to move from the first operating position to the second operating position in response to the change in tension in the control line.

According to one aspect of the invention the flow control mechanism allows water to flow through the delivery means in the first operating position and is arranged to move to the second operating position when the tension in the control line is diminished or released.

According to another aspect of the invention, the flow control mechanism is arranged to be held in the first operating position by the control line as long as the control line is under tension and to move to the second operating position when the tension in the control line is released.

Still further according to the invention, there is provided a method of irrigating land using delivery means for delivering water to the land and a flow control mechanism movable between first and second operating positions in one of which the flow control mechanism allows water to flow through the delivery means and in the other of which the flow control mechanism prevents the flow of water through the delivery means, the method including the steps of anchoring sensing means on the land at a position remote from the delivery means, and connecting the flow control mechanism by a control line under tension to the sensing means, the sensing means being arranged upon sensing a change in wetness in the land to change the tension in the control line and the flow control mechanism being arranged to move from the first operating position to the second operating position in response to such change.

When used in this specification and the claims, the term ‘control line’ is intended to include rope, string, cord, twine or any similar flexible monofilament or multifilament lines that are suitable for the purpose in hand. There are any number of commercially available products of this type that are inexpensive and strong so that, when they are connected to the flow control mechanism of a gate or other water delivery apparatus, they can be pulled taut enough to hold the flow control mechanism in a desired (i.e. open or closed) setting or move the flow control mechanism from one setting to the other.

Such control lines have the useful property that long lengths of them are light enough to be portable and can be looped into compact, bundles or, preferably, wound onto reels that can readily be carried from one bay to the next. It is easy to arrange for such control lines to serve as an inexpensive means of transmitting signals from the sensing means to all of the flow control mechanisms envisaged herein to cause the flow control mechanisms to function. Another functional advantage of such a line is that it is easy to devise means of rapidly reattaching it to the sensing means and the flow control mechanism after the sensing means has been moved to a new location. The importance of this lies in the fact that the optimum quantity of water that should be let into any bay is apt to vary from one watering to another. Irrigators learn from experience that the flow of water into a bay should be cut off when the water reaches a certain point in the bay. If the flow is cut off when the water reaches this point, there is enough water remaining on the surface to water the whole bay. The optimum distance between this point and the delivery mechanism can change from one watering to the next, the distance depending on, inter alia, the initial moisture content of the soil in the bay and the amount and state of the vegetation in the bay. The use of a control line as a communicating means facilitates the use of a portable sensing means that operates by sensing the arrival of the water at the sensing means.

The apparatus within the scope of the invention is simple and inexpensive to make, install and maintain and can be retrofitted to existing irrigation water delivery mechanisms of known type.

DESCRIPTION OF EMBODIMENTS ILLUSTRATED IN THE DRAWINGS

Examples of apparatus that embody the invention are described below with reference to the accompanying drawings in which: [0019]
FIGS. [0020] 1 to 3 are side views of a flow control mechanism for operating a gate, the flow control mechanism being shown in three in working positions over the gate;
FIG. 4 is an enlarged view of the lower part of the flow control mechanism; [0021]
FIGS. 5 and 6 are respectively a side view and a plan view of a sensor mechanism for actuating the flow control mechanism upon detecting the presence of water at the sensor mechanism; and [0022]
FIG. 7 is a schematic side view of a modified apparatus.[0023]
FIGS. [0024] 1 to 6 are drawn substantially to scale.
Referring first to FIGS. [0025] 1 to 4, the flow control mechanism 8 is designed to open and close a commercially available type of gate that is well known in Australia where it is called a Padman gate. One source of supply is Padman Stops Pty Ltd. Since the Padman gate is well known, most details thereof are not illustrated here and the gate is indicated schematically only at 12 in the drawings. The gate comprises a concrete casting having a base 2 from which arise two spaced apart posts 3. The closure takes the form of a flap 4 of strong elastomeric material located in the space between the posts and bolted along its edges to the base and the faces of the posts, forming a seal thereagainst. The flap 4 is shaped so that when the upper edge thereof, stiffened by a length of rolled steel angle bar 5 bolted thereto, is lifted to a raised position from a lowered position, the flap forms an effective dam, preventing water from flowing through the space between the posts. In the lowered position, the flap lies horizontal on the base, allowing water to flow through the space over the flap. A link chain 36 is mounted on the angle bar 5. A cross bar 34 (described further below with reference to FIG. 4) is mounted on the posts, spanning the space therebetween. The chain 36 is used to manually lift and lower the flap and, in conventional use of the Padman gate, is hooked onto to the cross bar 34 to hold the flap in its raised position.
The flow control mechanism [0026] 8 can also be used, without substantial modification, to operate (a) guillotine type gates in which the closure, which is flat and slides in vertical slots formed in the posts, can be raised by the flow control mechanism 8; and (b) simpler gates comprising merely a flexible pipe or large diameter hose that passes through the canal bank and has a projecting outlet end that can be raised by the flow control mechanism 8 above the level of water in the canal.
In the present example, the flow control mechanism [0027] 8 comprises a lever assembly 10 that includes two levers 14, 16 of length about 270 cm and 95 cm respectively. Each lever may be formed from 25 mm size square steel tubing. Two rectangular lugs 18, cut from 25×3 mm thick steel flat, bar are welded to the side faces 20 of the lever 14 at its lower end. The lower end of the lever 16 is inserted between the lugs and pivotably joined to the lever 14 by a pin 22′ that passes through aligned holes 22 formed in the lugs and in the side faces 24 of the lever 16. The relative positions of the lugs and the holes 22 is such that when the lever 16 pivots anticlockwise in the drawing to a position shown in FIG. 4 in which it is at right angles to the lever 14, the lower end of the front face 26 of the lever 16 comes into abutment with the lower end 28 of the lever 14.
At a short distance from the [0028] lower end 28, a pair of aligned holes are drilled in the side faces 20 of the lever 14. These holes receive a bolt 30′ by means of which the lever 14 is pivotably joined to a mounting bracket assembly 32 for mounting the flow control mechanism on the cross bar 34. This is the cross bar that, as mentioned above, forms part of the gate 12. The mounting bracket assembly comprises two posts formed from 25 mm square steel tubing. One of the posts 37 is short (about 130 mm) but the other 37′ is longer (about 90 cm). A lug 39, comprised of a short length of 25×3 mm thick steel flat bar, is welded to the back face 40 of each post at its lower end. A trunnion 42, comprised of 25×25×3 mm rolled steel angle bar of the same length as the lug 39, is welded to the front face 44 of each post. The cross bar 34 is fabricated from 25 mm wide square- or rectangular steel tubing so that the cross bar can pass between the respective inner faces 48, 50 of the lug 39 and the trunnion 42. Each post is seated on the cross bar and can be fixed in place by means of bolts (not shown) that pass underneath the cross bar through suitable holes in the lug 39 and trunnion 42.
The [0029] bolt 30′ passes through holes 30 drilled in the side faces of each post and is locked in place by means of a nyloc nut.
The [0030] trunnion 42 has a flange 56 that stands up from the front face 44 of each post. Holes 54 are formed in the centre of the flange. A support bar 58, for supporting the lever 14 in a raised position, is pivotably mounted in the holes 54. The support bar comprises a short length of 25×3 mm thick steel flat bar 60 to one end of which is welded a steel pin 54′ the ends of which project from the edges of the flat bar and are pivotably received in the holes 54. For reasons explained below, when the operating mechanism is being set up for use, the lever 14 is pivoted about the bolt 30′ (anticlockwise in the drawings) from a tilted position (shown in FIG. 2) to a raised position (shown in FIGS. 1 and 3). At the same time the support bar 58 is pivoted (also anticlockwise in the drawings) about the axis of the pin 54′ until the free end 62 of the support bar hooks under an abutment 64 to support the lever in the raised position. The abutment 64 takes the form of a short length of round steel rod welded to the front face 66 of the lever 14. The length of the support bar and the position of the abutment are chosen so that, when the lever 14 is so supported, it is disposed in a position that is suitable for a purpose that will be discussed.
Two [0031] bosses 68, 70 are bolted on lugs 72, 74, each cut from a short length of 25×3 mm thick flat bar, welded to the back face 76 of the lever 14 with a space therebetween. In the present case, baked clay electrical insulators are used for these bosses as they have smooth, low friction surfaces. The lugs have projecting portions 72′, 74′ that extend from the bosses away from the back face 76 of the lever.
A series of seven pairs of aligned [0032] holes 78 are drilled in the side faces of the lever 14 adjacent the upper end thereof. The holes are equally spaced apart a distance, in the present example, of 90 mm. Commercially available retaining clips (not shown) can be inserted through selected ones of these holes. In use, one or more counterweights are mounted on the upper end of the lever and the purpose of the clips is to retain the counterweights in position. In the present case, ordinary baked clay building bricks 80, formed with holes therethrough, serve very well as the counterweights.
A [0033] cleat 86, formed from a short length of 6 mm round steel rod bent to shape, is welded to the back face 25 of the lever 16.
A series of eight pairs of aligned [0034] holes 88 are drilled in the side faces 24 of the lever 16 adjacent the upper end thereof. The holes 88 are equally spaced apart. In use, the chain 36 that lifts the flap of the gate 12 is attached to the lever 16 by means of a bolt that passes through a selected pair of the holes 88.
Referring now to FIGS. 5 and 6, the [0035] sensor mechanism 100 comprises a body 102 cut from a length of 75×40×5 mm hot rolled steel channel section. A float assembly 104 is mounted on the body adjacent one end thereof. The float assembly comprises an arm 106 that carries a hollow plastics ball 108. The arm 106 comprises a short length (about 170 mm) of 25×3 mm steel flat bar to one end of which is welded a steel pin 110′. The ends of the pin 110′ project from the edges of the flat bar and are pivotably received in aligned holes 110 drilled in the flanges 112 of the body. The holes are located quite close (about 10 mm) to the bottom 114 of the channel. The ends of the pin 110′ are threaded to receive nuts for retaining the arm in the center of the body channel.
The [0036] ball 108 is provided with a threaded spigot 109 by means of which it is bolted to the arm 106. The ball is located near the outer end of the arm and projects downwardly from the lower face thereof.
The body also carries a [0037] lever assembly 120. The lever assembly comprises a lever 122 pivotably connected to a drawbar 124. Like the arm 106, the lever 122 comprises a short length (about 170 mm) of 25×3 mm steel flat bar 126. A block 128, formed from a short length of 25×10 mm rolled steel flat bar, is welded to the inner end of the bar 126. A slot 130 is formed in the block, extending from its free end 132 to close to the junction with the bar 126. A steel pin 134′ is welded to the end of the block, straddling the slot. The ends of the pin project from the sides of the block through aligned holes 134 drilled in the flanges 112 of the body. The ends of the pin 134′ are threaded to receive nuts for retaining the block in the body channel.
The [0038] drawbar 124 is formed from a length (about 310 mm) of 25×3 mm rolled steel flat bar 142. The bar 142 is oriented with its wide faces vertical so that it can enter the slot 130 in the block 128. The bar 142 is pivotably retained in the slot by means of a pin 144′ that passes through aligned holes 144 drilled in the block on either side of the slot and in the bar 142 near its inner end 146. A recess 148 is cut in the lower edge of the bar to accommodate the portion of the pin 134′ that straddles the slot when the lever 122 is pivoted (anticlockwise in the drawings) until it comes into contact with the arm 106 of the float assembly 104.
An [0039] end plate 152 is welded on the end of the channel 102. A hole (not visible in the drawings but referred to later in this description as hole H) is drilled in the center of the end plate. A short length (about 100 mm) of 8 mm round steel rod 150 is welded to the outer end of the bar 142 in alignment with the longitudinal axis thereof. The rod 150 is screw threaded for most of its length and passes through the hole H. Compression springs 154, 156 are mounted over the rod on either side of the end plate 152. The inner spring 154 is located between the end plate and a seating cup 158 seated on the end of the bar 142. The outer spring is located between the end plate 152 and a seating cup 160 held in place by a nut 162 mounted on the end of the rod 150.
One or more short lengths (about 50 mm) of steel rod may be welded to the outer face of the bottom of the [0040] channel 102 to acts as pegs 160 for anchoring the sensor mechanism in the ground.
In what follows reference is made to the pivotal axis X of the pin [0041] 144′ and an imaginary line L that passes through the center of the hole H and the axis of the pin 134′ about which the lever 122 pivots. Axis X and line L are not shown in the drawings but it is convenient to refer to them as such to facilitate this description. In use, for the sensor mechanism 100 to function properly, the body 102 must be disposed approximately horizontal with the channel opening upwards. In practice the sensor mechanism will be resting on the ground at this time and it will be necessary for the operator to dig a small hole in the ground to accommodate the ball 108. To set the sensor mechanism, the arm 106 of the float assembly is pivoted (anticlockwise in the drawings) until the arm rests on the bottom 114 of the channel. In this movement the ball moves into the hole that has been dug in the ground. The lever 122 is now pivoted (clockwise in the drawings) to drive the drawbar 124 towards the end plate 152. At the end of this action, the spring 156 is fully decompressed and there is a space between the inner end of the spring 156 and the end plate. The end of a control line 170, which in the present case is comprised of bailing twine, is inserted in this space. The lever 122 is now pivoted (anticlockwise in the drawings) to draw the drawbar 124 towards the float assembly. This action causes the spring 156 to be compressed and the control line end is gripped firmly between the inner end of the spring and the end plate 152. The lever 122 is pivoted until it comes into contact with the arm 106. In this action the pivotal axis X of the pin 144′ moves downwardly across the imaginary line L. This causes the spring 156 to lock the lever 122 in place against the arm 106. Consequently, the twine end is locked to the sensor mechanism until the hole in the ground in which the ball 108 is accommodated begins to fill with water. When this happens the ball, being buoyant, is lifted up and causes the arm 106 to lift the lever. The lever consequently pivots upwardly until it comes into contact with the arm 106. In this action the axis X of the pin 144′ moves upwardly across the line L. At this point the drawbar 124 springs towards the end plate 152 under the action of the spring 156. In this sudden movement the spring 154 absorbs the shock to the drawbar and the twine end is released.
To use the [0042] sensor mechanism 100 and the operating mechanism 8 in conjunction to feed water to a bay, it is necessary first for the operator to decide at what point in the bay the water must reach before the water is cut off. This has been discussed above and, for convenience, it will be called the cut off point. For the purposes of this description, it is assumed that a gate of the Padman type has been installed to feed the water to the bay. However, any other type of water delivery mechanism that can be operated by the sensor mechanism 100 can be used. Some alternative gates are discussed above and it is believed that there are probably other types of suitable delivery mechanisms.
The sensor mechanism is driven into the ground at the cut off point and set up as described above, gripping the end of the control line. It may be noted that the length of the control line will nearly always make it necessary for the control line to be stored on a reel. The operator now moves to the gate carrying the reel and paying the control line off the reel as he goes. [0043]
It is assumed here that the operating mechanism [0044] 8 has been installed over the gate. When the operating mechanism is installed, the chain 36 that was previously hooked onto the cross bar 34 to hold the flap of the gate in the raised position is connected to the lever 16 by means of a nut and bolt that is anchored in one of the hole pairs 88. It is assumed that, during a previous watering cycle, the lever 16 and hence the flap of the gate have been lifted to the raised position. In these circumstances the lever assembly 10 will be in the position shown in FIG. 2 with the lever 14 tilted over. To set the lever assembly up for use, the operator may temporarily hook the chain 36 on the post 37. It is not necessary nor desirable to disconnect the chain from the lever 16 for this purpose but it enables the lever 16 to continue to support the flap in the raised position during the next step in the process which is to lift the lever 14 to the raised position. The support bar 58 is next hooked under the abutment 64 to hold the lever 14 in the raised position. The operator now retrieves the control line and, after passing it around the boss 68, draws it taut before wrapping it several times around, and tying it to, the projecting portion 72′ of the lug on which the boss 68 is mounted. The tautened control line will now hold the lever 14 in the raised position and the support bar 58 can be unhooked from the abutment 64.
The final step is to detach the [0045] chain 36 from the post 37 and allow the lever 16 to pivot downwardly until its lower end comes into abutment with the lower end 28 of the lever 14. In the process, the flap of the gate drops and allows water to commence flowing through the gate into the bay.
When the water reaches the cut off point in the bay, the water starts to fill the hole in the ground in which the [0046] ball 108 of the sensor mechanism has been inserted. Only a small amount of water enters the hole before the ball is lifted sufficiently to trip the lever assembly and release the control line. This releases the tension in the control line and causes the lever 14 to gravitate to the tilted position. This in turn lifts the lever 16 carrying the flap of the gate to the raised position and cutting off the flow of water through the gate.
The apparatus described can be arranged, after watering of a first bay is complete, to open and subsequently close a gate set up in a second bay. For this purpose it is necessary for the second bay to be equipped with second operating and sensor mechanisms which are conveniently identical to the [0047] respective mechanisms 8, 100. These second mechanisms are not shown in the drawings but are conveniently referred to in what follows as mechanism 8/2 and mechanism 100/2 respectively.
To arrange the opening and subsequent closing of the gate in the second bay, it is assumed that the [0048] mechanism 100/2 is located at the cut off point in the second bay and that the lever 14 of the mechanism 8/2 has been set in the raised position as shown in FIG. 3 and already described with reference to mechanism 8.
The control line from [0049] mechanism 100 is first passed around the boss 68 of mechanism 8. Instead of being attached to the lug 72 of mechanism 8, the control line is passed around the post 37′ of mechanism 8 and led to mechanism 8/2. After lifting the lever 16 of the mechanism 8/2 to the raised position (as shown in FIG. 3) the control line is passed around the post 37′ of mechanism 8/2, pulled taut and attached to the cleat 86 on the lever 16 of mechanism 8/2. With the apparatus set up in this manner, when the mechanism 100 releases the control line attached thereto, the lever 14 of the mechanism 8 will drop, causing the gate in the first bay to close as already described. However, the lever 16 of the mechanism 8/2 will also drop, pivoting anticlockwise about the pin 22′, to open the gate in the second bay.
The gate in the second bay will thereafter be closed when the [0050] mechanism 100/2 is tripped by the water in the second bay and releases the control line attached to the lever 14 of mechanism 8/2.
Using the methods described, each bay in a series can be watered one after the other with no need for an operator to be in attendance once the apparatus has been set up. [0051]
It is advantageous to use a sensor mechanism that releases a control line (as opposed to pulling it) to actuate an operating mechanism. More energy would be required for an operating mechanism that is actuated by drawing the line in to function and such an operating mechanism would be more likely to be triggered accidentally if the tension in the line increases, as for example, when tripped by over by a person or by stock. However, the use of such a sensor mechanism is not ruled out. [0052]
Clearly, the flow control mechanism [0053] 8 could be made to work by arranging that the control line is slackened off rather than being completely released. The scope of the present invention is thus intended to extend to a sensor mechanism that reduces the tension in the control line rather than releasing it completely.
Other known types of water delivery mechanisms could be adapted to be actuated by a sensor mechanism that releases or pulls a control line when triggered. There are many systems in which the opening or closing of a gate is carried out by mechanised means. Such means include an electric motor, a spring, a water driven turbine, a gas strut or a hydraulic or pneumatic ram. In practice, any such systems would usually be provided with switching means for actuating the mechanised means. Alternative switching means, operated by the flexible control, could be designed and used without difficulty and the advantages of using such a control line might well warrant the substitution in either existing or new installations. [0054]
An example of the use of a sensor mechanism to control an electrically operated gate is shown schematically in FIG. 7. The [0055] gate 200 is opened and closed by an electric motor 202. Power for driving the motor is provided by circuitry 204 that includes suitable switches, including a toggle switch 206 that must be closed to cause the motor to close the gate. Conventionally, the toggle switch is manually operated. In the present case, prior to the gate closing operation, the gate is open and the switch 206 is in the open position. One end of a tension spring 210 is anchored on a bracket 212 mounted adjacent the switch 206. The other end of the spring 210 is provided with a loop 214 that can be passed around the toggle 216 of the switch when the spring is stretched. After being attached to the sensor mechanism 100 as described above, the control line 170 is pulled taut and attached to the loop to hold the spring stretched with the loop around the toggle as described. When the sensor mechanism 100 releases the control line, the spring retracts, drawing the toggle with it and thus closing the switch 206.
The [0056] switch 206 could alternatively be arranged to actuate a solenoid that trips a spring or gas strut that closes an existing gate; or to open a valve that feeds water, hydraulic fluid or air to the turbine or ram that closes an existing gate.
In some circumstances it may be considered preferable to avoid digging a hole for receiving the [0057] ball 108 of the sensor mechanism 8. In one arrangement for dealing with this case, the sensor mechanism is provided with a peg 160′ having a pointed end and located at the same end 103 of the body as that at which the float mechanism is located. The sensor mechanism is set up as previously described except that the end 103 is supported above the ground by the peg 160′ which is not initially driven into the ground. When the water arrives at the peg 160′, it softens the ground and the peg sinks into the ground under the weight of the sensor mechanism. In the process the ball 108 comes into contact with the ground and lifts off the bottom of the channel, triggering the lever assembly to release the control line.
This method may be unsuitable for use where the ground is too soft or too hard. For example, if the ground is sandy is may be too soft to support the sensor mechanism on the [0058] peg 106′. Conversely, ground that is too hard may not allow the peg to sink into the ground even when it is wet.
Further, it may be necessary to ballast the sensor mechanism or to construct it of heavier materials to ensure that it is heavy enough to drive the peg into the wet ground. It may also be necessary to provide the body with outriggers to stop the sensor mechanism from falling over when the control line is pulled taut. To this end the [0059] end plate 152 may be replaced by a length of rolled steel flat or angle section whose ends project from either side of the body.
An advantage of the invention is that the equipment is simple, cheap and easy for the operator himself to repair. The components are not as susceptible to water damage as electrical or electronic components would be. [0060]
In the foregoing, the constructional details, including the sizes and dimensions of the components, are provided for ease of understanding and are not intended to limit the scope of the invention to components constructed or having dimensions as described. [0061]

Claims

1. Apparatus for use in irrigating land, the apparatus comprising an anchoring device arranged to anchor a control line under tension in the land, means to detect a change in wetness in the land and means to cause the anchoring device to change the tension in the control line in response to a change in such wetness.

2. Apparatus according to claim 1, in which the means to detect the change in wetness comprises means to detect an increase in water level at a chosen locality in the land.

3. Apparatus according to claim 2, in which the means to detect the increase in water level comprises a float, the apparatus comprising means to connect the float to the anchoring device in such manner as to cause the anchoring device to change the tension in the control line when the float rises with a rise in the water level.

4. Apparatus according to claim 1, support means is provided for supporting at least a portion of the anchoring device above the land, the support means being arranged to sink into the land when the land softens as a result of an increase in wetness in the land.

5. Apparatus according to claim 4, in which the support means comprises at least one member having a pointed end that is arranged to sink into the land.

6. Apparatus according to claim 1, in which the means to cause the anchoring device to change the tension in the control line comprises means to grip the control line and to release the control line in response to a change in wetness in the land.

7. Apparatus according to claim 6, in which the means to grip the control line comprises a spring, the apparatus comprising means for putting the spring under load when the control line is to be gripped, and to release the load in response to a change in wetness in the land.

8. Apparatus for use in irrigating land, comprising delivery means for delivering water to the land, a flow control mechanism movable between first and second operating positions in one of which the flow control mechanism allows water to flow through the delivery means and in the other of which the flow control mechanism prevents the flow of water through the delivery means, an anchoring device arranged to anchor a control line connected under tension to the flow control mechanism, means to detect a change in wetness in the land and means to cause the anchoring device to change the tension in the control line in response to a change in such wetness, the flow control mechanism being arranged to move from the first operating position to the second operating position in response to the change in tension in the control line.

9. Apparatus according to claim 8, in which the flow control mechanism allows water to flow through the delivery means in the first operating position and is arranged to move to the second operating position when the tension in the control line is diminished or released.

10. Apparatus according to claim 2, in which the flow control mechanism is arranged to be held in the first operating position by the control line as long as the control line is under tension and to move to the second operating position when the tension in the control line is released.

11. Apparatus for use in irrigating land, comprising an anchoring device substantially as herein described with reference to the accompanying drawings.

12. A method of irrigating land using delivery means for delivering water to the land and a flow control mechanism movable between first and second operating positions in one of which the flow control mechanism allows water to flow through the delivery means and in the other of which the flow control mechanism prevents the flow of water through the delivery means, the method including the steps of anchoring sensing means on the land at a position remote from the delivery means, and connecting the flow control mechanism by a control line under tension to the sensing means, the sensing means being arranged upon sensing a change in wetness in the land to change the tension in the control line and the flow control mechanism being arranged to move from the first operating position to the second operating position in response to such change.