Abstract:
A method of determining the surface level of an area subject to flood, furrow or surface irrigation. The method includes the steps of providing at least one measuring cup positioned below the surface level but within the area and providing a water level sensor within or integrated with the at least one measuring cup. The levels provided by the water level sensor are used to calculate the surface level by determining the inflection point between the rapid increase of the monitored levels when the front of irrigation water passes the water level sensor. A further aspect of the disclosure is the provision of a soil moisture sensor, said sensor comprising an auger adapted to be inserted into the ground with minimum soil disturbance, said auger having means for measuring soil moisture.

Description:
CLAIM OF PRIORITY 
     This application is a continuation of and incorporates by reference International Application No. PCT/AU2010/001125, filed Sep. 1, 2010 and published as WO 2011/026177 A1 on Mar. 10, 2011, entitled “A Method of Determining Surface Level, and a Soil Moisture Sensor,” which claims priority to Australian Patent Application Ser. No. 2009904225, filed Sep. 3, 2009. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a method of determining the surface level at a location of an area subject to flood, furrow or surface irrigation and relates particularly, though not exclusively, to determining the depth of water and the volume of water above the surface level. This method also defines when the surface irrigation water front arrives at the location. 
     BACKGROUND OF THE INVENTION 
     Flood, furrow or surface irrigation is a method of passing a volume of water over a confined surface in order to achieve a desired soil infiltration. Modern laser-grading techniques have allowed large areas (or bays) to be defined and accurately graded so that improved efficiencies can be achieved. In addition, high flows of water onto bays are resulting in improved water application efficiencies on many soil types. Most bays are rectangular in shape and graded to a uniform slope. 
     The challenge is to apply the correct amount of water to an irrigated crop using flood or surface irrigation such that:
         1. The depth of infiltration is consistent with the required depth of infiltration of the crop throughout the entire bay.   2. There is no over-watering such that no excess water runs off the end of the bay, and no under-watering such that water does not reach the end of the bay—the precise time to stop the flow onto the bay.       

     The difficulties in this task are:
         a. The infiltration rate of the soil is unknown, and so although the volume of water applied is known (by multiplying the time of application by the measured flow rate), the infiltrated volume is unknown and so the remaining volume of water above the surface must be measured.
           Although the infiltration rate is likely to be consistent across the bay, it can vary from irrigation to irrigation.   
           b. To determine the volume of water above the surface, the depth of water above the surface must be measured and multiplied by the area of coverage. The difficulty in measuring depth is defining the surface level, or the datum above which the depth is measured. The depth of flow can vary from irrigation to irrigation due to factors such as crop density and resistance it makes to the flow or the existing soil moisture.   c. Traditional measurement of the ground level is not a simple or reliable process, as it requires a detailed survey to determine mean ground level. It is difficult to achieve the required accuracy due to the localized unevenness of the soil and to determine the point at which to record the surveyed surface level measurement. To reduce this error, many measurements need to be taken from which to derive the mean ground level.       

     Objects of the Invention 
     Accordingly it is an object of the present invention to provide a method of determining the surface level of an area subject to flood or surface irrigation which overcomes these problems and allows an accurate measurement of the surface level. 
     A further object of the invention is to allow calculation of the volume of water needed for the desired irrigation. 
     SUMMARY OF THE INVENTION 
     In a first aspect of the invention there is provided a method of determining the surface level of an area subject to flood, furrow or surface irrigation, said method including the steps of providing at least one measuring cup positioned below the surface level but within said area, providing a water level sensor within or integrated with said at least one measuring cup, monitoring the levels provided by said water level sensor and calculating said surface level by determining the change point between the rapid increase of said monitored levels when the front of said irrigation water passes said water level sensor. 
     In a still further form of the invention there is provided a soil moisture device including an auger adapted to be inserted into the ground with minimum soil disturbance and means on said auger to measure soil moisture. 
     In a yet further form of the invention there is provided a method of determining the volume of water of an area subject to flood, furrow or surface irrigation, said method including the steps of providing at least one measuring cup positioned below the surface level of the ground but within said area, providing a water level sensor within or integrated with said at least one measuring cup, monitoring the levels provided by said water level sensor and calculating said surface level by determining the change point between the rapid increase of said monitored levels when the front of said irrigation water passes said water level sensor and calculating the volume by using the difference between said calculated surface level of the ground and the detected water levels from said water level sensor after the passing of said irrigation water front. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an implementation of the invention and, together with the description, serve to explain the advantages and principles of the invention. In the drawings: 
         FIG. 1  is a cross-sectional view of an example of a measuring cup and level sensor used in a preferred embodiment of the invention; 
         FIG. 2  is a similar view to that of  FIG. 1  showing the water flow of an area subject to flood irrigation with the measuring cup and level sensor in position; 
         FIG. 3  is a graphical representation of the water level measurement of the level sensor in  FIG. 2  against time; 
         FIG. 4  is a larger view of  FIG. 2  showing the calculations that can be made according to the method of the invention; 
         FIG. 5  is a plan view of a first embodiment of an auger which can be combined with the measuring cup shown in  FIG. 1 ; 
         FIG. 6  is a side view of the auger shown in  FIG. 5 ; 
         FIG. 7  is a top perspective view of the auger shown in  FIG. 5 ; 
         FIG. 8  is a second embodiment of an auger which can be combined with the measuring cup shown in  FIG. 1 ; 
         FIG. 9  is a side view of the auger shown in  FIG. 8 ; and 
         FIG. 10  is a top perspective view of the auger shown in  FIG. 8 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following detailed description of the invention refers to the accompanying drawings. Although the description includes exemplary embodiments, other embodiments are possible, and changes may be made to the embodiments described without departing from the spirit and scope of the invention. 
     Wherever possible, the same reference numbers will be used throughout the drawings and the following description to refer to the same and like parts. For the purposes of the specification the word “comprising” means “including but not limited to”, and the word “comprises” has a corresponding meaning. Also a reference within the specification to document or to prior use is not to be taken as an admission that the disclosure therein constitutes common general knowledge in Australia. 
     In  FIGS. 1 to 4  of the drawings there is shown an irrigation system  10  which incorporates the features of the invention. The irrigation system  10  has a bay  12  which has the ground  14  graded to provide a slope. Water  16  can flow through a gate or gates  18  from an open channel  20 . Water flows along the ground slope  14  and any excess water will be caught by open channel  22  at the end of bay  12 . The theory is to provide enough water to provide a consistent infiltration into the ground for the crop being grown but not to have insufficient or excess water draining into open channel  22 . The amount of water entering gate or gates  18  can be accurately measured for ensuring that the water allotment is not exceeded. However it is difficult to determine whether under-or over-watering occurs. The invention provides a measuring cup  24  which is set into the ground  14  and is below ground level. Measuring cup  24  can be any shape, for example cylindrical, and has a base  26  and sidewalls  28 . In  FIG. 1  the sidewalls  28  are tapered to form a frusto-conical shape. Located within measuring cup  24  is a water level sensor  30  which can constantly detect the level of water  16  passing at that point. The water levels are constantly monitored by a computer controlled system (not shown) which can supervise operation of gate or gates  18 . 
     The invention provides a method to determine the surface level  42  by measuring the rise of water in measuring cup  24 . There will be a rapid rise of the water level in measuring cup  24  which is filled when water front  34  reaches measuring cup  24 . Once measuring cup  24  fills, the localized effect disappears and the movement of the passing water front  34  controls the rise in water level. The point of change  40  between the rapid rise  36  of the filling of measuring cup  24  and the more gradual rise  38  of the passing of the water front  34  is the point of the surface level  42  of ground  14  at the position of measuring cup  24 .  FIG. 1  also shows that the measuring cup  24  can vary in depth in the ground.  FIG. 1  shows a typical ground level  14  but the ground level could be higher as shown at  14 A and  14 B. In the levels at  14 A and  14 B there will be a greater filling time before the water flows past the water level sensor  30  as the water front passes. 
     Similarly the passing of the water front (the tailwater  44 ) is asymptotic towards the point of surface level  42 . This tailwater method is useful in checking and calibrating the point defined from the water front method. 
     As described herein, the water front method is needed to compute the depth of water  32  above ground  14  as it is passing and a constant depth of flow passes. Once a constant depth is achieved the volume above the surface back to point of inflow onto bay  12  can be determined. The input from monitoring the water level sensor  30  allows the change point  40  between the localized rate of filling principle to determine the measurement point of the mean ground level. Once the mean ground level  42  is detected as a point within the measurement range of the sensor  30 , the depth of water  32  above ground level  14  can be determined by subtracting the surface level detection point from the sensor measurement. 
     This approach removes the need to know the absolute elevation of the water level sensor  30  relative to the mean ground level, as the water level sensor  30  now measures both the water depth  32  and the mean ground level  42  and provides a differential measurement which is not relative to the absolute position of the water level sensor  30 . The depth of installation of the measuring cup  24  does not effect the measurement of depth above mean ground level, provided measuring cup  24  is below mean ground level. 
     When the water level sensor  30  is placed at a certain position (typically mid way along bay  12  between channels  20  and  22 ) and typically along the centreline of bay  12  it is possible to determine, once the maximum depth has been achieved, the following:
         1. The volume applied to bay  12  up to the time water front  34  reaches the sensor position.   2. The volume above the surface level  42  up to the time water front  34  reaches the sensor position.   3. The infiltration up to the time water front  34  reaches the sensor position (the difference between 1. and 2. above).   4. The infiltration volume needed to complete the irrigation through to the end of bay  12 .   5. The derivation of the cut off point  46  along the bay  12  at which the water front  34  arrives and the flow onto the bay  12  should stop.   6. The time for the water front  34  to reach the cut off point  46  and therefore close the gate or gates  18  and stop the flow onto bay  12 .       

       FIG. 4  shows the integers that are used in the determination of cut off point  46 . 
     The integers are as follows: 
     a; distance from gate  18  to sensor  30   
     b; distance from gate  18  to cut off point  46   
     c; distance from gate  18  to open channel  22   
     t a ; time for water front  34  to reach sensor  30   
     t b ; time for water front  34  to reach cut off point  46   
     t c ; time for water front  34  to reach open channel  22   
     d s ; water depth above surface level  46   
     d i ; infiltration depth of water into the ground of bay  12   
     w; bay width (assume constant, although could vary) 
     Q; flow rate onto bay  12  (assume constant, although could vary) 
     Q w ; flow per unit width (Q w =Q/w) 
     V w ; wedge volume (FIG.  2 )—volume of water between water front  34  and the point at which full depth  48  is reached. (assume the wedge volume is negligible for the purposes of this example i.e. full depth  48  is at the point of water front  34 ) 
     When the water front  34  arrives at the sensor  30 ;
         1. Total volume applied per unit width=Q w ×t a      2. Volume above surface per unit width=a×d s      3. Infiltration volume per unit width=a×d i          

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     The remaining volume of water (per unit width) at time t a  needed to accurately complete the irrigation;
 
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     The method described above is for the use of one sensor  30  in a bay  12 . The use of multiple sensors (not shown) can be used to give a more detailed measurement of the water level as well as the rate of travel of the water front. 
       FIGS. 5 to 10  illustrate a further aspect of the invention, namely an integrated soil moisture sensor  50 . The ability to measure soil moisture enables determination of the optimal time to irrigate or apply water to the crop. The moisture sensor  50  can be used to allow measurement and calibration of the infiltration depth d i ; of water into the ground of bay  12  as previously discussed with reference to  FIG. 4 . 
     Traditional direct read soil moisture devices are vertically embedded into the soil. The techniques to measure soil moisture are capacitance or Time Domain Reflectometry (TDR). The problems with vertical embedded soil moisture sensors (capacitance or TDR) is the propensity for the water to run down the side (and the region of disturbed soil) of the vertical embedded sensor. 
       FIGS. 5 to 7  show a central tube or column  52  with an external spiral  54  secured or integrated with central tube or column  52  to form an auger. In this embodiment the top section  56  of central tube or column  52  forms the measuring cup  24  with an internal base (not shown). Measuring cup  24  could also be separately attached to the central tube or column  52  as an alternative. 
     External spiral  54  can include at least one matching pair of: 
     1. capacitance plates facing each other; or 
     2. TDR probes attached thereto at the spiral edge. 
     Both alternatives could have multiple pairs or a combination of both pairs. The pairs could take advantage of alternate or offset spirals to mount each of the cooperating capacitance plates or TDR probes. The preferred option is to have two parallel plates with the pitch of the plates 180 degrees apart. 
     The advantage of the auger is that water is less prone to run down the inclined surface of the spiral  54  as compared to a vertical interface with the soil. 
     In  FIGS. 8 to 10  spiral  54  has discontinuities or breaks  58  such that at locations of the discontinuities  58  the soil will bind and prevent water running down the line of soil disturbance. Each segment or section of the discontinued spiral would then form a defined soil moisture device for a given depth—which is useful information for understanding the moisture content in soils. The discontinuities  58  typically traverse any desired degrees of arc. 
     The invention is not to be limited to the preferred embodiments described with reference to the drawings. Measuring cup  24  may be perforated to allow the measuring cup  24  to slowly empty when irrigation is completed. This will ensure that the measuring cup  24  will be empty for the next irrigation cycle. 
     Further advantages and improvements may very well be made to the present invention without deviating from its scope. Although the invention has been shown and described in what is conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope and spirit of the invention, which is not to be limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent devices and apparatus.