IRRIGATION AND ITS PRACTICE.

New Zealand Journal of Agriculture, Volume XXVIII, Issue 3, 20 March 1924, Page 145

IRRIGATION AND ITS PRACTICE.

i. THE CENTRAL OTAGO REGION AND SCHEMES.

R. B. TENNENT, N.D.D.,

Instructor in Agriculture, Dunedin, and J. K.

MARKS, A.M.Inst.C.E., M.N.Z.Soc.C.E., Resident Engineer, Public Works Department, Alexandra.

'np'HE arid to semi-arid region of Central Otago extends over about THE arid square miles, comprising interior the southern 5,000 square miles, comprising the interior of the southern •*“ portion' of the South Island where the Island attains its greatest

width. Of this area 75 per cent, is mountainous country, not suitable for agriculture or other classes of intensive farming, but is used for sheep-grazing, being mostly held in large areas of several thousand acres each for that purpose. The remainder of the district demands only irrigation and close settlement to become one of the most highly productive districts in the Dominion.

In its early history Central Otago gained prominence and great notoriety when gold was discovered in the beds of several rivers. A rush of miners from every part of the Dominion and from other countries took place, small communities of eager gold-seekers rose up all Over the country, and from being a district inhabited by only a few pastoralists, it was in a very short space of time changed into one of hustling excitement. Races necessary to convey water to sluicing claims far removed from the rivers were constructed with unwearying patience until they extended in a network of small channels all Over . the country.

In due course the gold boom died a natural death, and the floating population attracted to Central Otago by the gold lure gradually drifted away. A few miners living in hope or too old to break fresh trails remained on their claims, but, finding that the amount of gold procurable would barely suffice to keep 1 them in food and clothing, were forced to augment their scanty earnings by the growth of vegetables and such produce as they required for their own use. Realizing from bitter experience the futility of depending upon the rainfall for moisture sufficient to the needs of their crops they utilized the . water-races primarily designed to facilitate the, extraction of gold from the soil for the purpose of conveying water to their crops in time of drought. This then, was the birth of irrigation in Central Otago.

At a later date two officers in the Public Service* were deputed to report on the possibilities of systematic irrigation in this dry region. As a result of their observations they came to the conclusion that over a quarter of a million acres of land were capable of being irrigated, and pointed out that such land if so treated would probably yield very satisfactory results. There can be no doubt that this estimate was very conservative, and it. is quite safe to say that between four and five hundred thousand acres of suitable land are irrigable.

From time to time small streams have been dammed or diverted from their original course and spread over the adjacent land, with the result that the present-day traveller in Central Otago, wending his way through arid areas, meets the refreshing sight of snug orchards with trees bearing fruit comparable with the finest in the world, and comfortable farms growing a wealth of j lucerne and other crops, these being the outcome of individual effort and a realization of the efficacy of applying water to the soil. - '

Unfortunately, it is not possible for each and every settler in the district to have an ever-flowing stream for his own private use, and consequently if no assistance were given by co-operative endeavour Central Otago would be in fifty years' time much as it was fifty years ago. During the past decade, however, considerable progress in agricultural development has taken place, and this has been the direct outcome of the application of water to the land. Facilities for doing this have been afforded by the establishment of several fairly comprehensive Government irrigation works, and numerous smaller private schemes. The amount of public money thus expended will undoubtedly. prove of national benefit; but having inaugurated the irrigation works and delivered the water to the farmers it now remains to be shown how most judiciously that water may be utilized, what crops are best grown tinder irrigation, and the most practicable methods of applying the water to crops on different grades and types of land.

Although irrigation farming is older than any other kind of highly developed agriculture in the world, it is nevertheless a fact that the average settler in New Zealand has had no experience in its practice. Since the advent of irrigation in Central Otago people of all sorts and conditions have been coming there to take up land.

Most of them come with the pose of making comfortable' homes on the land and of earning a living by farming, but one finds among them many individuals who' know little or nothing of farming, as well as those who lack the physical qualities necessary to cope successfully with the varying conditions of a settler’s life.

* J. L. Bruce and J. H. Dobson, “Irrigation in Central Otago," 1909.

It is not generally recognized that it takes as much capital and more agricultural skill to develop and bring into production an irrigated farm than is required to successfully farm in a humid district. The need of a fairly comprehensive series of articles dealing with irrigation in Central Otago has been felt for some time past, and with this object in view the present writers have undertaken to prepare such matter in the hope that it will be of use to irrigators, by presenting to them in simple condensed form the fundamental principles of irrigation and the practical application of those principles to their daily work on the farm. . DESCRIPTION .OF CENTRAL OTAGO. A brief description of the area dealt with in this article will be of use to intending settlers, and a glance at the general map of Central Otago ' (Fig. 2) will serve to illustrate the chief irrigation localities. This map shows, enclosed within a circle of approximately forty miles radius, with Clyde as its centre, what might be termed the semi-arid region of Otago. The country is intersected by ranges of mountains between which are valleys rich in fertile soil. These valleys lie at an altitude varying from 500 ft. to 1,500,ft., and to this may be attributed the variations in climatic conditions which .exist throughout the district. •

During winter heavy falls of snow occur on the. mountain ranges. This naturally conserved water, in the form of snow up on the high country, gradually becomes available for use in the valleys as the warm season approaches. Were it not for the fact that heavy falls occurred, then the difficulty of obtaining water for irrigation purposes would practically prove insurmountable. As it is each valley is traversed by a river, and in spring numerous smaller streams rush down the mountain-sides. The damming of such streams and the conservation of their water-supply is one of the problems with which the irrigation engineer is confronted ; it is the regulation of such streams by dams which assures the settlers in the valleys of a oontinuous supply of water for their crops throughout the dry season.

Central Otago may be regarded as fairly well equipped in the matter of roads and railways. The- formation of roads in this district is a comparatively easy matter, due to the presence of splendid road-forming gravel which exists everywhere, and to the natural drainage of the porous subsoil, which allows the surface of the roads to dry almost immediately after the cessation of rain.

From an economic point of view it is of interest to note that trees are practically non-existent in this region (Fig. 3), but for fuel* purposes nearly every township has in close proximity deposits of lignite of a fairly good quality. Electric power and light is already being supplied to settlers in certain. portions of . the district, and the reticulation of other areas and townships is in progress. Lime deposits do not occur

in great number, there-being- as a matter of fact, a scarcity in this respect. On the side of Lake Wanaka there is a fairly large deposit of limestone of good quality, which is frequently used by farmers in the immediate neighbourhood, and there is no doubt that in the future provision will be made to enable irrigators to procure abundant supplies from this source.' An interesting and important deposit also occurs at the south end of Lake Hayes (Fig. 4). Professor Park, reporting on this deposit, states that “ the material is excessively fine in texture, and so soft as to be easily excavated by a spade without exercising much force. Its purity and verent form renders it of great economic value for agricultural purposes, both for dressing the land and in the manufacture of manures.”

Soil. Conditions. • • . The plains and river-terraces of Central Otago have been, built up of . the softer portions of the metamorphic schists, forming deep micaschist soil which responds in a wonderful way to cultivation and irrigation (Fig. 5). The fertility of the soil is notorious, and appears to be the outcome of a happy combination of physical and chemical characteristics. Captain Hutton, F.R.S., in 1875 (" Report on the Geology of. the Goldfields of Otago,” page 95) stated that the soils of Otago taken as a whole are decidedly above the average in quality, and:this appears to be owing to the great extent of mica-schist exposed at the surface, . the decomposition of which has supplied more or less directly almost all the soil in the province. That, this schist contains a considerable amount of lime is proved by the incrustation in nearly

all the caves occurring in it ; and the good quality of the soil derived is well seen in the Dunstan district, which is remarkably fertile when irrigated. ”

Mr. B. C. Aston, writing in the Journal for June last, gives it as his opinion that “ the fertility of the mica-schist soils of Otago is due not to lime or potash or to the total amount of phosphoric acid they contain, but to the comparatively large amount of available phosphoric acid present, a point of great theoretical and practical importance.” The fact that available phosphate is abundant in these Otago soils but deficient in most New Zealand soils, especially those of the North Island and northern parts of the South Island, suggests that some day Central Otago, with its splendid summer climate and irrigation possibilities, will become one of the finest farming districts in New Zealand.

The same writer points out that this amount of available phosphoric acid would probably equal a dressing of from 8 cwt. ■to 16 cwt. of phosphoric acid per acre, which would take from 2 J tons to 5 tons of superphosphate to supply. If the computation is correct, then the marvellous results obtained from this soil are explained.

The following table (adapted from Mr. Aston's article) gives some analyses of Central Otago mica-schist soils' made in the Department’s Chemical Laboratory from time to time : —• .

The composite sample was made up of samples of soils from Roxburgh (two), Beaumont, Naseby, Sutton, Manuherikia, Maniototo, St. Bathan's, and Frankton. This analysis supports the statement of Professor Park in Bulletin No. 2 of the Geographical Survey, that “ the soil possesses a latent, richness that the casual observer would hardly suspect. By the application of water the wilderness is transformed into fruitful gardens and' prosperous farms. The conservation and distribution of water for irrigation purposes will in time convert the plains and valleys of Central Otago into one of the most prosperous agricultural districts in New Zealand.” While it is true that a large percentage of the soil is of first-class quality, it must be borne in mind that, like most districts, a diversity of soils exists. Thus in Ida Valley the character of the subsoil is quite different from that obtaining in the Manuherikia Valley, in. that the former is of a close clay texture and the latter of a free open nature

largely intermixed with waterworn gravel. Again, cropping out from deep deposits of schist soil appear large beds of lighter gravel, in character so porous- as to make the application of water to them, while in their natural state, a difficult and wasteful matter. As will be shown later, there is a very intimate relationship between these different types of soils and the methods required to irrigate them.

Rainfall. When it is borne in mind that the average rainfall over the South Island is in the vicinity of 45 in. per annum, then it will be realized that Central Otago, with an annual fall averaging slightly over 15 in. and ranging from 12 in. to 20 in. per annum, is in a most unfavourable situation insofar as rainfall is concerned. Fig. 6 illustrates in graphical form the average monthly rainfall and temperature of the irrigable lands, and demonstrates the necessity of augmenting this low summer rainfall. From this graph it will be observed that the average rainfall during the growing-period — to March inclusive —is approximately 8-8 in., and that during the month of February the average rainfall is the lowest for the year, being approximately in. During that month, however, .the highest temperatures throughout the year are recorded, and when it is borne in mind that the mean shade temperature for the whole month is 79 0 F. it will be understood how excessive is the -heat, and consequently how great must be the evaporation of moisture from the soil. During February, therefore, more frequent irrigations must be given to growing crops. GOVERNMENT IRRIGATION SCHEMES COMPLETED OR UNDER CONSTRUCTION. Brief details of the Government schemes completed or under course of construction in Central Otago will be of use, and the information is given in tabulated form in the accompanying Table 2. In the case of the Ida Valley scheme, the area is admirably adapted for dairy-farming and the raising of beef or mutton (Fig. 7).The growing of special seed crops such as clover, &c., would appear to offer good remuneration to the farmers there. On account of its height above —namely, 1,500 ft.-the conditions are net favourable' for fruit-growing except in some sheltered spots. General mixed farming, and especially lucerne-growing, present great possibilities. As regards the other irrigation areas mentioned in Table 2, practically any type of farming can be successfully practised on them, but there is no doubt that intense cultivation combined with either dairy-farming, the raising of stock, or fruitgrowing will give , the most satisfactory results.

In addition to the schemes already in hand the Government has also investigated an extensive tract of country in order to ascertain the feasibility, or otherwise of irrigating further areas of land. As a result of such investigations it is now realized that a much greater extent of country can readily be utilized for irrigation, as shown in Table 3. .

Even with the inclusion of the projects detailed in Table 3 the possibilities' of irrigating further tracts of country are by no means exhausted. The district abounds in potential hydro-elecric power projects capable of developing immense amounts of power, and when the industries of the Dominion warrant the harnessing of one or more of these there are very great possibilities for the use of their surplus energy for pumping irrigation water during the periods of the twentyfour hours when the demand for other purposes is low. By thus working to the convenience of the usual power-requirements of other industries it should be possible to apply power to irrigation pumping

at low cost, while at the same time probably justifying the undertaking of such power schemes at an earlier date than might otherwise appear warranted. With cheap 'hydro-electric power there is no doubt that many areas not now being investigated as potential irrigation settlements, chiefly because an economic gravitational supply of water is not available, would be dealt with by pumping water from the larger rivers and lakes.

INDIVIDUAL, COMPANY, AND LOCAL-BODY UNDERTAKINGS. Irrigation development has also been . successfully . carried out, or is at present in progress through individual effort, by companies, or by local bodies. Works undertaken by individual effort, comprise a hundred or more small areas scattered throughout the district, generally in the most favourable situations, which involve a minimum of construction cost. There are, however, a few instances where more enterprising settlers have confidently and successfully constructed irrigation works of considerable magnitude, involving in some instances the loading of their farms with construction costs running into several thousands of pounds. Among the most notable of these individual irrigation undertakings are those of Mr. John Wilson, at Lauder; Mr. P. R. Sargood, at Wan aka ; Mr. Lee, at Lake Hayes ; Mr. Lethbridge, at Ardgour; and Mr. R. K. Smith, .-at Tarras. The lastmentioned undertaking has recently been acquired. by the Crown for enlargement and extension. The total area of lands under irrigation by individual .effort is estimated by the writers at 10,000 acres. . There are .only, two instances of companies , being formed to construct irrigation worksnamely,- the Little Valley, development party and the Cromwell Development Company. The former have acquired

abandoned mining water-races and are developing them with a view to irrigating 1,000 acres of land. The Cromwell Development Company has undertaken and practically completed works of very considerable magnitude and of a most interesting nature which will provide irrigation for probably 4,000 acres or more (Figs. 10 and 11). . There are three Iccal-body schemes, all under the Vincent County Council—namely, Bannockburn (about 1,700 acres), Matakanui (about 5,000 acres), and Blackman’s (about 1,000 acres). The two former are in a state of development, only about half of the areas being yet supplied with water, while • the last-named has, been in full operation for many years.. . SUMMARY OF IRRIGABLE AREAS. The following table gives a summary of all the areas in Central Otago capable of irrigation by gravitation and pumping methods.

(To be continued.)

149

l, ; , of head is water Cusec term The * The term “ Cusec’' denotes a flow of water equivalent to 1 cubic foot per second. It is. synonymous with the old mining term a “head ” of water.

No. Laboratory Locality. Vol tile Matter. .. Nitrogen. -per-cent Citric-acid Extract, Dyer’s Method, Hall’s Modification (Available Plant-food). Hydrochloric-acid' Extract (Total Plant-food). <0 . 0 On Ignition. Lime, CaO. Magnesia, MgO. • ■ 20 ft oi ow O "O' Ph .2 « 0 T3 £•3 CL, < Lime, a CT <L CaO. d Magnesia. MgO. 1% b ow .9. ® yi ~ s 0 3} d 'Id ft C-I O M - Ph .2. « tn ~ C T5 A< L 295 Earnscleugh 2-48 4-60, 0-140 0-014 0-052 o-35 0-38 - - 0-20 O-IO B 944 Cromwell 0-64 o-34 . 0-080 O-OII 0-069 0-41 I-OI 0-16 0-24 T II Alexandra 32-00 1’12 0-056 0-008 0-064 ,1 77 Maniototo 4-52 5-95' 0-189 0-031 0-041 P 278 Composite sample 1-92 6-05 0-254 o-i97 0-055 0-037 0-031 1-23 1-02 )2 o-66 o-66 0-09 0-09

Table 1. —Chemical Analyses of Central Otago Micaceous Soils.

of Name Source Flow Natural of Canal Maximum Average Annual Gross Area Area now being Remarks. Capacity. Average Rainfall. included. irrigated. Annual Rainfall. Gross Area included. Area now being irrigated. Remarks. ' 'Cusecs. Cusecs. Inches. Acres. Acres. . conservation dams to Valley Manorburn, Poolburn, small no Practically (■' 109 15’39 28,600 ,OOO streams in . winfully Galloway Ditto ter water conserved in Manorburn Dam 15 13’77 1 ,3°° 900 Completed. Terrace . Ditto , IO 13'77 1,600 500 Completed. ter water conserved in Manorburn Dam ‘ 15 13-77 13’77 1 , 3°° I ,600. 900 500 Completed. Completed. • • • • • • IO No. River . 77 TOO 14-22 000 II, 3.500 Completed. Ardgour. . River (estimated) 50 20 21-75 ,OOO ,OOO Completed. Tarras . . River (estimated) 7°. 21-75 7,000 4OO construction. Under Conservation dam may be necessary. Earnscleugh Fraser River 8 20 15-86 4 , OOO I , IOO Partially completed. Conservation dam will be eventually required. Last Chance Shingle, Gorge, and 11 20 17-87 4.300 700 Under construction. Coal Creeks Available water only sufficient for full irrigation of 2,000 acres and partial irrigation of balance. Teviot River Teviot River and Lake 40 (estimated) 80 21-97 3.000 300 Under construction. Onslow Dam Bengerburn Bengerburn Creek . . 5 21-97 1, 000 Under construction. Totals . . 63,800 21,4OO 'V Conservation dam • / may be necessary. • Earnscleugh ■ . 8 20 15-86 4,000 1,100 Partially completed. River ... Shingle, damConservation eventually will required. 11 20 f 17-87 4>3oo 700 Under construction. Coal Creeks Available water only sufficient for full irrigation of 2,000 acres and ♦ ■' partial irrigation of balance. Chance Last River Teviot 40 (estimated) 80 21-97 ' 3.000 300 Under construction. and Teviot Dam Onslow Bengerburn Creek . . 5 21-97 1., 000 Under construction. Bengerburn .. Totals . 2 I,4OO 63,800 .

Table 2.- Government Irrigation Schemes completed or under Construction.

Scheme. Name Water-supply. Source FlowMinimum River. Average Annual • Rainfall. Area . approximately irrigable. Remarks. Cusecs.* In. . Acres. Also presents possibilities for hydro-electric power development with water before use for irrigation. and Cromwell Lowburn Stream Meg Cusecs.* 29 21'75 3,750 29 In. 21-75 . Acres. 3,750 Also presents possibilities for hydro-electric power development with water before use for irrigation. Upper and 77 17’59 100,000 Two or three, large storage dams Rivers . -i will be necessary. 77 17’59 TOO, 000 Two or three large storage dams will be necessary. Maniototo . River Taieri 25 18-34 150,000 require dam A storage building.River Teviot Lake .' 40 ‘ 21-97 - • 13,400. Lake Onslow Dam will require Onslow • I- . : . enlarging. 40 2i-97 13,400 Lake Onslow Dam will require enlarging. Arrow River (estimated) 32-18 6,500 scheme., Gully and Creek Dam 14-91 100 scheme. Flats Bendigo River Lindis 50 21-75 3,000 Gravity development Creek ... (estimated) 24-96 4,000 scheme. Gravity Total 280,

Table 3.- Further Government Schems investigated.

Area actually under Irrigation — Area actually under Irrigation at 30th January, 1924Works under Construction mostly expected to be completed during 1924. Areas investigated and considered Feasible for Development by Gravitational Water-supply. Further Areas estimated as probably irrigable when Cheap Power available [for Pumping. Totals. Government Individual Company . . Local body Acres. 21,400 10,000 4,350 Acres. 42,400 5,000 3,350 Acres. 280,750 ■ Acres. 42,350 Acres. 386,900 10,000 5,000 7,700 Totals 35,750 50,750 280750 42,350 409,600

Table 4. -Summary of all Irrigable Areas.