the effects of a roster system on irrigation frequency

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The effects of a roster systemon irrigation frequencyP. D. Fitzgerald a & W. R. Lobb aa Winchmore Irrigation Research Station ,Department of Agriculture , Private Bag, AshburtonPublished online: 14 Feb 2012.

To cite this article: P. D. Fitzgerald & W. R. Lobb (1966) The effects of a rostersystem on irrigation frequency, New Zealand Journal of Agricultural Research, 9:3,729-737, DOI: 10.1080/00288233.1966.10431562

To link to this article: http://dx.doi.org/10.1080/00288233.1966.10431562

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THE EFFECTS OF A ROSTER SYSTEM ON IRRIGATION :FREQUENCY

By P. D. FlTZGERALD* AND W. R. LOBB*

(Received 15 Scptemher 1965)

ABSTRACT

An investigation, covering 36 irrigation seasons, was made of the effect of a fixed fortnightlY roster system on irrigation demands on Mid-Canterbury Irrigation Schemes. Irrigation was applied on a roster day if the deficit equalled or exceeded 1 in. Frequency of irrigation, periods of moisture stress, dates of first irrigation, and month by month distribution of irrigations were determined. Under automatic irrigaton the roster system studied would be practical.

INTRODUCTION

729

On any large irrigation scheme it is impossible to supply water on demand, and some method of allocating water on a roster system must be used. The major irrigation schemes in the Mid-Canterbury area are the Ashburton-Lyndhurst (64,000 acres), Mayfield-Hinds (84,500 acres), and the Valetta-Tinwald (49,500 acres). At present water for all of these schemes is provided from the Rangitata Diversion Race, which is designed to carry 1,000 cusecs.

The roster system on these schemes is designed to allocate water on consecutive days, Sundays excepted, on a shifting system; that is, if the first day on which water is supplied this week is a Tuesday, then in the following week the first day of supply will be a Wednesday. This system has been designed so that no farmer will receive water on a succession of Saturdays, live stock sale days, or on meeting days, which are usually on fixed days of the week.

The duty of the water provided is not the same on all schemes, but it would be desirable that the duty would be such that the irrigable area of a farm can be totally irrigated during the time water is allocated. A uniform duty of 1 cusec to 100 acres is assumed in this study; this is at present the proposed duty for future schemes in Canterbury. Water is delivered to farms in a flow of 8 cusecs.

However, it is not the object of this paper to investigate this type of roster system. The roster system investigated is a fixed day one, in which roster days always occur on the same day of the week. This type

* Winchmore Irrigation Research Station, Department of Agriculture, Private Bag, Ashburton.

N.Z. Jl agric. Res. 9: 729-37

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730 Irrigation roster system

of roster would give stability to irrigation deliveries. Although it could not be adopted at present, with the increasing spread of automatic irriga-tion (Lobb and Hall 1963; Lobb 1964) it will eventually be possible to use such a system. When automatic irrigation is fully developed it will no longer matter whether the roster day falls continually on any specific day, as the attendance of labour during the irrigation will be unnecessary.

There are two principal reasons for studying the effect of a roster system. One is to study the effect of choice of a roster on an individual farm. The other is to determine the number and distribution of irriga-

TABLE I. No. of irrigations

Irrigation possible fortnightly commencing September

2 3 4 5 6 7

1927-28 5 6 5 5 5 6 6 1928-·29 8 7 8 6 5 5 4 1929-30 6 5 6 7 6 7 7 1930-31 5 6 6 6 6 5 5 1931-32 9 8 9 8 9 9 8 1932-33 8 9 8 8 7 7 8 1933-34 4 4 4 4 3 4 4 1934-35 8 8 7 7 7 8 7 1935-36 7 7 7 7 7 7 6 1936-37 3 3 4 5 5 5 4 1937-38 8 8 7 5 5 5 5 1938-39 8 <) 8 8 7 7 8 1939--40 8 8 8 8 8 8 8 1940--41 7 7 7 7 6 6 7 1941-42 7 7 7 7 6 7 7 1942--43 5 5 5 8 7 5 6 1943--44 8 7 7 7 7 7 6 1944--45 3 4 4 4 4 3 3 1945--46 7 7 7 6 6 6 7 1946-47 5 5 5 4 4 5 5 1947--48 7 8 8 10 10 10 9 1948--49 6 7 7 8 8 8 8 1949-50 6 6 6 6 6 6 8 1950-51 4 5 4 3 4 4 4 1951-52 7 8 8 7 8 8 6 1952-53 3 5 4 6 6 5 5 1953-54 8 8 8 7 6 6 6 1954-55 11 10 9 10 10 10 10 1955-56 10 10 9 9 9 8 7 1956-57 7 6 6 6 5 5 6 1957-58 6 6 6 7 7 6 6 1958-59 8 8 9 10 10 9 8 1959-60 9 8 8 8 7 7 8 1960-61 5 5 4 4 4 4 4 1961-62 10 10 10 10 9 9 8 1962-63 7 7 7 9 8 7 6

Total 243 247 242 247 237 234 230 Mean 6.8 6.9 6.7 6.9 6.6 6.5 6.4 Range 3-11 3-\0 4-10 3-10 3-10 3-10 3-10

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8

P. D. FITZGERALD AND W. R. LOBB 731

tions so that a scheme is properly engineered to meet the demands that wiII be made upon it. This involves a study of extreme demands coupled with a knowledge of water availability. If the water is not enough to meet these demands, standards can be set so that the demand can be met in a high percentage of cases.

It was decided to investigate the effect of a fortnightly roster system on the number of irrigations required. The period of investigation was the 36 seasons 1927/28 through 1962/63.

9 10 11 12 13 14 Range

5 5 5 5 5 5 4 4- 6 4 4 4 4 4 6 7 4- 8 7 7 (, 6 7 6 6 5- 7 6 (, 6 5 5 6 5 5- 6 8 8 7 8 8 9 10 7-10 8 9 10 II 9 8 8 7-11 4 6 5 4 5 4 4 3- 6 8 9 8 8 8 8 8 7- 9 7 5 6 6 7 7 7 5- 7 4 5 4 4 5 4 3 3- 5 5 6 5 5 6 7 8 5- 8 8 7 7 7 6 6 7 6- 9 9 9 8 9 9 8 8 8- 9 8 11 11 11 11 11 9 6-11 7 7 7 7 7 7 7 6- 7 7 6 6 5 5 5 5 5- 8 7 7 8 8 8 8 9 , 6- 9 3

, 2 3 ,1 4 2 2- 4 .,

6 6 7 7 7 8 7 6- 8 4 4 5 5 4 4 4 4- 5 8 7 7 7 7 7 8 7-10 7 7 7 7 7 6 6 6- 8 7 8 7 s 6 6 6 I 6- 8 6 5 5 5 5 5 4 3- 6 6 6 7 7 7 7 7 6- 8 5 6 4 2 3 3 3 2- 6 8 9 9 8 8 8 8 6- 9

11 11 10 11 11 11 \0 9-11 9 9 9 8 7 9 9 7-10 6 7 5 6 6 8 8 5- 8 6 8 8 7 7 6 6 6- 8

10 10 8 7 8 8 8 7-10 8 9 9 9 9 9 9 7- 9 5 5 6 6 5 5 6 4- 6 9 11 11 10 10 10 10 8-11 6 6 5 F, 6 6 7 5- 9

242 254 244 243 242 245 243 6,7 7.1 6.8 6.8 6.7 6.8 6.8

3-11 3·11 2-11 3-11 3-11 3-11 2-10 I

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METHODS

The available moisture in the Lismore Shallow SiIt Loam is 2.4 in. on irrigated areas. As this soil type covers large areas of the present schemes and is representative of the majority of the remaining soil types covered by these schemes, the investigation of roster frequency was based on the physical characteristics of this soil type. For several years a field experi: ment has been conducted at the Winch more Irrigation Research Station on production levels when irrigation is applied at various soil moisture

TABLE 2. Number of days that deficit is above 1 ill.

Irrigation roster fortnightly commencing September

Year 2 3 4 5 6

1927-28 1928-29 1929-30 1930-31 1931-32 1932-33 1933-34 1934-35 1935-36 1936-37 1937-33 1938-39 1939-40 1940-41 1941-42 1942-43 1943-44 1944-45 1945-46 1946-47 1947-48 1948-49 1949-50 1950-51 1951--52 1952-53 1953-5.1 1954-55 lQ<;,-,(;

1956-57 1957-58 1958-59 1959-60 1960-61 1961-62 1962-63

Total Mean Range

I

I

I

I

41 39 61 43 64 70 47 60 44 48 45 62 55 62 67 47 50 40 "A 34 66 63 44 56 60 48 70 57 r;n

45 44 72 66 44 53 43

1,914 53

34-72

i

I

44 42 64 :'\3 78 65 29 63 47 41 58 60 57 62 56 48 60 23 54 37 60 59 47 48 56 31 74 67 r;1

56 45 75 70 45 56 50

1,921 53

23-75

I i I

t I

I

I

I

I

I.

\

I I

I

I

44 44 52 34 Ii4 70 33 65 43 38 66 62 63 59 42 52 56 27 53 41 69 48 47 38 56 44 82 n r;3 6 52 47 71 52 47 60 57

1,913 53

27-82

-----.-.-~

I

46 flO 44 39 59 73 37 62 44 27 57 65 59 63 57 34 48 30 57 53 53 47 53 43 63 32 72 68 70 48 41 66 51 47 66 60

1,874 52

27-73

,

I

I i

I I

50 65 48 35 45 70 52 62 38 32 58 r;o 60 69 62 41 61 33 56 34 61 50 55 17 55 32 68 70 65 53 5fl 70 56 49 74 64

1,926 54

17-74

I 1

I

I

46 52 51 42 47 67 3.1 54 39 35 48 62 63 71 50 49 60 25 54 24 57 49 47 21 59 34 70 75 69 55 71 67 59 52 77 71

1,906 53

21-77

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deficits (measured by the gravimetric method). In this trial the highest production was secured when the soil moisture was not allowed to drop below the 50% available level (1.2 in. deficit). The difference between production at this level and production at the 25% available level (1.8 in.) deficit was not very great.

The frequency of applying irrigation at these deficits (1960/61-1964/65) averaged eight for the 1.2 in. deficit, and 4.6 for the 1.8 in. At wilting point (2.4 in. deficit) the average number of irrigations was 2.6.

7 8 9 10 11 12 13

I

[ I 1

50 48 50 47 42 48 50 53 52 48 43 45 48 41 41 , 60 46 58 55 41 45 44

I 46 44 46 55 5': 41

59 59 66 76 68 71 67 70

I

59 57 50 <13 60 62 37 40

I

2R 33 35 38 41 54 ,19 39 45 i 46 50 52 33 38 45 40 44 43 46 40

I 28 32 36 40 37 35

49 51 45 67 57 40 36 64 58 58 57 60 81 69 67 62 59 61 56 50 60 66 61 41 47 53 52 54 49 4'i 49 53 55 58 64 47 45 56 59 62 53 52 59 '\9 43 42

I

47 53 61 24 25 25 27 21 33 37 37 40 44 38 44 51 47 27 30 28 23 25 28 31 70 77 80 80 74 69 68 67 59 44 44 54 44 56 47 53 47 52 54 56 53 24 23 28 33 38 43 48 72 75 78 52 56 63 66 38 42 36 49 i 51 44 45 73 62 55 53 55 56 64 78 72 73 82

i

66 68 70 78 79 81 76 74 83 63 48 49 50 54 56 56 36 76 ~I 59 51 43 44 50 63 55 58 68

I

68 66 69 58 61 56 60 50 55 58 56 39 34 33

I

38 54 53 8'5 73 57 63 68 73 74 77 73 60 60 51 41 44

[

I

I

I

,980 I 1,908 I

1,799 1,858 I

1,849 1,905 1,908 55 . 53 50 52 51 53 53

4-85 23-81 25-81 23-80 I

21-74 28-83 31-69

I I ,

I \ I

14

51 42 57 40 61 67 36 55 46 45 38 79 57 70 50 48 50 45 56 35 67 60 41 52 70 46 71 70 62 41 44 72 62 36 63 37

1,922 53

36-79

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To evaluate the likely number of irrigations over the period 1927/28 to 1962/63, the deficit was calculated from climatic data. The method used was that of Thornthwaite (1948). This had been shown to give reliable results in Mid-Canterbury (Fitzgerald and Rickard 1960; Rickard 1957).

If a farmer on the scheme keeps a rain gauge and also obtains forms from the Winchmore Irrigation Research Station, giving average potential evapotranspiration for each month, he can keep account of his soil moisture deficits by a simple book-keeping method. Hall (pers. comm.) had used this method on a 160 acre unit of the Winchmore Irrigation Research Station to apply a deficit to a roster system in practical farming. He had made the decision to irrigate if the deficit was 0.5 in. or greater on a roster day, and found this meant irrigating on most roster days unless they were preceded almost immediately by rain. The number of irrigations exceeded 13 in each season. The deficit level was then altered to 1 in. and the number of irrigations fluctuated between seven and 10. As could be expected from the results of the experiment quoted above, this resulted in a good level of production. On the basis of this it was decided to combine a fortnightly roster with a 1.0 in. deficit.

The climatic data necessary to apply Thornthwaite's method was obtained from the Ashburton Meteorological Station for the seasons 1927/28-1962/63 and prepared in a suitable form for processing by an IBM 650 computer. A programme was written which allowed for irrigation to be applied if the deficit exceeded 1 in. and the day was the roster day. As the roster was based on a fortnightly intervaL this gave 14 different roster days.

RESULTS

Ffject of roster day on number of irrigations

Table 1 shows the number of irrigations according to roster day and season. It will be seen that the average number of irrigations and the range of number of irrigations is approximately the same on all roster days. This table also shows the range in number of irrigations within each season; in some years this range is quite wide, e.g., 1952/ 53, two to six, 1932/33, seven to 11. Inspection of the table shows that the season with least water use was 1944/45, with an average of 3.3 irrigations and range two-four; the year with the greatest water use was 1954/55, with a mean of 10.4 irrigations and a range of nine-II.

Efject of roster day on soil moisture stress

An investigation was also made to determine the extremes of soil moisture depletion under these irrigation regimes. It was found that under this system the soil moisture never reached wilting point. Accordingly, the measure of soil moisture stress adopted was the number of days the deficit exceeded 1 in. Table 2 shows this information for each roster day. Although, on the average, the number of days above 1 in. deficit is the same for all roster days, the ranges are quite different. When these

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figures are averaged within years, the year with the least number of days above 1 in. deficit is 1944/45, and the year with the greatest number is 1954/55.

Effect of roster on date of first irrigation

For each roster day and irrigation season the date of the first irrigation was extracted from the computer sheets. It is not considered necessary to reproduce all these dates here, and a summary of them is given in Table 3. It can be seen that in some seasons there is quite a large

1927-28 1928--29 1929-30 1930-31 1931-32 1932-33 1933-34 1934-35 1935-30 1936-37 1937-38 1938-39

TABLE 3. Range of dates of first irrigation for each year

14/10 - 18/ 1 4/l0 - 17/l0 9/10 - 22/10

11/11 - 22/12 13/10 - 26/10 6/10 - 27/12 4/10 - 17/10 4/11 - 17/11 3/10 - 16/10 7/10 - 31/10

11/10 - 29/10 3/10 - 23/11

1939-40 1940-41 1941-42 1942--43 1943-44 1944-45 1945-46 1946-47 1947-48 1948-49 1949-50 1950-51

7/10 - 20/l0 21/10 - 3/11 30/9- 13/10 14/11 - 27/11 3/11 - 25/11

15/11 - 1/ 2 2/11-15/11

28/11 - 25/12 23/10 - 19/11 29110 - 11/1 1 26/ 9 - 9/10 3/l0 - 13/11

1951-52 1952-53 1953-54 1954-55 1955-50 1956-57 1957-';S 1958-59 1959-60 1960-61 1961-62 1962-63

261 9 - 20/11 181 9 - 1/ 1 22/ 9 - 12/11 29/ 9 - 12/10 11/10 - 24/10 23/ 9 - 21/11 231 9 - 20/H) 21/ 9- 4/10 17/ 9 - 301 9

8110 - 2/11 6110 - 19/10 2/10 - 20/10

variation in starting dates. From the original table the month in which the deficit first reached 1 in. was determined. The frequency of occurrence by months was September-28%, October-56%, November-17%. A further breakdown of this distribution shows that irrigation was never necessary in the period 1-15 September; in 69% of seasons the date of the first irrigation was in the period 16 September to 15 October.

It should be noted that for farmers on this roster system the starting date for irrigating can vary quite widely; for instance, in 1952/53 farmers on roster days 4 to 8 commenced irrigation in September. For those on roster day II irrigations did not commence until January, a difference of 15 weeks. This indicates the effect of a variable rainfall.

Effect of roster day on length of irrigation season

From a knowledge of the dates of the first and last irrigation for each roster day the length of the irrigation season can be calculated. The average season length ranged from 151 days for roster day No.6 to 160 days for roster day 12. In any given year the length of the greater period decided how long it would be necessary to supply water. The average was 174 days, with a median value of 168 days.

Month by month distribution of irrigation

Table 4 shows the total distribution of irrigation month by month. This reveals that September was the month of least irrigation and January

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. T

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riga

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192

7-28

to

1962

--63

occ

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on

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4 5

6 7

8 9

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11

12

Sep

tem

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6 7

2 2

2 i

2 3

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5 4

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19

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43

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13

24

27

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19

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243

247

242

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I 23

7 23

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2 25

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the month of greatest irrigation. An assumption of the calculations (and one that would be made in practice) is that the soil is at field capacity at the beginning of September.

DISCUSSION

Given a duty of 1 cusec to 100 acres, it would appear highly practical to use a fixed two-day fortnightly roster. As can be seen, no advantage accrues to the choice of initial roster day. either in the number of irrigations or in the periods of moisture stress.

From the number of irrigations applied and the fact that wilting point was never reached, it is concluded that such a system would produce a reasonable level of irrigations for all farmers on the roster. In the average. this is less irrigations than would be applied at the 50% available level (8.0), but more than applied at the 25% available level (4.6). so a reasonably high level of pasture production should be assured. It is. of course, less than half the number of irrigations that would be applied if irrigation water was used on each roster day.

With a duty of 1 cusec to 100 acres, the irrigation rate necessary to achieve total irrigation within two rostered days a fortnight is 2.4 acres per hour. This is not an unreasonable figure under automatic irrigation; total irrigation will only be achieved conveniently under automatic irrigation, as it will require full day and night use of the water.

For the years under study irrigation commenced 10 times in September (eight of these occurred in the last 12 years). All these occurred in the period 16-30 September. Thus 1 in. deficit is reached quite frequently in the latter half of September. On the basis of this the irrigation season should not be curtailed beyond the first two weeks of September for the alternative LIse of hydro-electric generation.

ACKNOWLEDGMENT

The assistance of the Staff of the Biometrics Section of the Department of Agriculture, particularly that of Mr N. S. Mountier, is gratefuIly acknowledged.

REFERENCES

FITZGERALD, P. D.; RICKARD, D. S. 1960: A comparison of Penman's and Thornthwaite's method of determining soil moisture deficits. N.Z. JI agric. Res. 3: 106-12.

LOBB, W. R. 1964: New developments in irrigation techniques. Proc. 14th Lillcoln Call. Fmrs' Cant. pp. 96-103.

LOBB, W. R.; HALL, A. D. 1963: Automatic irrigation. N.z. JI Agric .. 106: 318-27.

RICKARD, D. S. 1957: A comparison between measured and calculated soil moisture deficit. N.z. JI Sci. Technol. A.38: 1081-90.

THORNTHWAITE, C. W. 1948: An approach toward a rational classification of climate. Geogr. Rev. 38: 55-94.

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the effects of a roster system on irrigation frequency

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