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  IT has already been stated that the greatest available water storage capacity exists in the soil itself. The association of Keyline cultivation and this water storage capacity has already been explained.

  If all rain which falls on crop and pasture land could be absorbed into the soil, there would still be areas remaining that do shed most of the rain that falls on them. Farm roads and yards, the homestead and other farm buildings and sheds, and often main roads, shed considerable quantities of rain. Conservation of this water for farm use is of the utmost importance.

  Whether a farmer realises it or not, he is dealing with forces that need the full use of engineering planning. A sudden storm may send 100,000 tons or 500,000 tons of water on to a 1,000-acre area in an hour or two. This huge weight of water can be controlled and conserved by the farmer to the great benefit of the land and himself, or it can run largely to waste, leaving a trail of destruction in its path.

  Levels are important factors in any water control and conservation project. These need to be used to advantage by the farmer. Contours and other level considerations are basic land engineering factors. The farmer must know how and when to use them.

  The application of Keyline methods requires very little levelling work, but those levels that it does require are of great importance.

  On undulating country, dams can usually be located which will enable the farmer to enlist the forces of gravity to provide him with water under pressure. This will give him a better farm, easier work and higher yields. Other things being equal, the value to a farmer of conserved water is in direct proportion to the height of the storage. The dams of potentially greatest value are those in his high country.

  The Keylines, by crossing the valleys at their first main point of slope flattening, will invariably position the highest suitable valley storage area for water.

  In any plan of general land development, the control of water is one of the first considerations. At the same time, it is to be kept in mind that Keyline Absorption-fertility is going to reduce run-off water very considerably. It may even completely stop run-off water from farm and pasture paddocks, except in the rare, but under present conditions, very dangerous period of general heavy flood rains. With the absorption of what previously would have been heavy run-off, consideration has to be given to conserving water from every available source.

  With the Keyline positioning the highest suitable dam sites, it becomes important to locate potential water-shedding areas above the Keyline.

  The Keylines have been illustrated as contour lines in the discussion on cultivation for the sake of simplicity.

  For purposes in connection with the conservation of water in the Keyline dam, the Keyline itself is a gently falling line to form a drain or water race to carry water to the dam. The use of the Keyline, which is now a drain, is still fully effective as a guide for Keyline cultivation.

  It is usually convenient and good practice from most other viewpoints, to locate the homestead and all farm buildings and the yards and their attendant roads in the higher country. From the point of view of full Keyline development, it becomes a part of planning to do so, in order to secure abundant run-off water to fill the Keyline dams from these sources.

  Wherever it is possible and practical, dams are constructed on the Keyline in the valleys, and the Keyline itself is pegged and constructed as a gently falling drain to carry water to the Keyline Dams.

  Keyline dams are constructed with a pipeline through the wall or through the floor to one side of the centre line of the valley, so that the full gravity pressure of the conserved water is available for spray irrigation and other farm purposes.

  Where areas of land exist that are 50 feet or more vertically lower than the Keyline, the water from the Keyline dam will supply effective pressure for irrigation without pumping. This "line of effective water pressure" suitably forms the top boundary for the irrigation paddocks. A 4-inch pipe through the wall, controlled by a 4-inch gate valve, in these circumstances will control gravity pressure which, often from a single dam, will effectively operate a comprehensive spray irrigation and stock-watering system.

  With the use of a 4-inch pipeline, the vertical drop from the water level to a nearby irrigation area multiplied by 0.4 will give the approximate pounds pressure available in the spray line. A vertical fall of 50 feet multiplied by 0.4 gives a twenty pounds per square inch pressure, which is suitable for operating most types of spray lines. As the spray line is moved downhill a little on each "move", there is, of course, an increase in available pressure.

  Referring to Map 4, which exhibits the same land area as Map 3, the Keyline crossings of the valleys are to be considered as possible dam sites. The sites marked in four of the valleys could be considered good dam sites. The site of the Keyline crossing of the fifth valley is not as suitable as the others.

  The most valuable water storage site for a Keyline dam is located in the first valley, as this site has the greatest area of land below It which Is suitable for irrigation by gravity sprays. This fact indicates a rule or general formula for determining the direction of flow of the Keyline when it is formed by a drain. If the creek or drainage line below a series of valleys--as in Map 4--has a general fall greater than five feet per thousand feet--the fall recommended for the Keyline drain--the direction of the Keyline fall follows that of the creek. When the creek has a flatter fall than required by the Keyline drain, the drain falls in the direction opposite that of the creek. This is illustrated by the shaded area on the map.

  The construction of a Keyline dam will often cost considerably less than a pump and engine installed for spray irrigation. The Keyline dam, its pipe and valve outlet, will operate the same sprays with no pumping cost.

  This low cost water is used in the general programme of progressive soil development, and higher yields will be incidental and automatic to the Keyline Absorption-fertility programme.

  The following construction comments should be considered.

  Most undulating country is suitable for dam construction if correct preparation and compaction of the material in the wall is secured. Fine clay, which is usually considered the best material for dam bank construction, has its own particular problem. This material in the wall of the dam will tend to "jell-up" below the waterline to such an extent that the weight of the wall above this wet unstable material may squeeze the material outwards from the wall, thus causing a central subsidence of the wall which extends down below the water line. This would result in the water overflowing at this point and would completely destroy the bank.

  In shale country the mixture of shale and clay will give the best possible material for bank construction.

  Before laying in a dam bank, the foundation area of the bank must be treated first according to the type of country. In shale country it is necessary to remove only the darker topsoil material to one side-this can be used later to cover the bank to obtain a quick growth of grass. This cleared area is then ripped before the wall filling material is placed on it. The material for the wall should be placed on in layers of from 6 to 12 inches thick, so that suitable compaction of the soil takes place during construction. Bulldozers will give sufficient compaction usually without the need of further special compacting implements.

  The back of the wall of the dam, that is the side away from the water, should not be specially compacted. If water seeps through the compacted front of the wall into the centre, it must be allowed to get out through the back of the wall, otherwise it may build up hydrostatic pressure inside the wall. This could destroy the wall by forcing or breaking the material from the back of it.

  Clean water seeping through a dam wall is usually quite safe, but a seepage that is discoloured by the wall material should be considered a danger to the wall itself. Raking or harrowing of the side of the wall in the water of the dam is usually the best means of sealing this type of seepage.

  In the construction of this type of dam by bulldozers, the excavation of the sides of the dam, if the land will stand firm, should be made on as steep a slope as the implement will dig. The water-side of the wall, as formed by the action of the bulldozer pushing the material upwards, should be flatter than the excavated sides. Usually the limitations of the implement to push material up the slope of the wall will form a wall of suitable slope.

  The laying of a pipeline through the wall of the dam, or through the earth below the wall of the dam, requires some special attention.

  The danger to be avoided here lies in the fact that water will tend to flow along the outside of the smooth pipe, creating an ever-widening and larger hole, which may eventually let all the water go and so destroy the wall.

  The following method of laying these pipes has been found completely satisfactory.

  After the wall site has been prepared by clearing away the topsoil material and the subsoil ripping, a trench to receive the pipeline is dug

  across the wall area a little to one side of the centre line of the valley fall. This trench is to be at least three times the diameter of the pipeline in width and depth.

  A 12 x 12-inch trench is required for a 4-inch pipe. The pipeline is laid in this trench with three or four large loose flanges 12 to 16 inches diameter. These are placed around the pipe from the inside of the wall to about its centre line.

  At each flange along the pipeline trench, two or three bucketfulls of wall material mixed with about 20 per cent. of some lightweight material is placed around the pipe. The trench is then filled in with adequate tamping of the material up to the surface level of the trench. It is important that this material should have the same moisture content as the wall material.

  The special mixture at each flange of the pipes will tend to seal the leak .if water does commence to flow along the outside of the pipeline. Some of this lightweight material will move to the small openings and will automatically re-seal them.

  In granite country it may be necessary to excavate a considerable portion below the wall site down to the depth of the firmer decomposed rock to prevent complete loss of water through the material below the wall..

  If this work is done properly and the bank consolidated in layers of six to nine inches deep, dams in this country will hold water effectively. Without this work these dams will often not hold any water.

  The High Contour dam is the highest dam of the Keyline plan. It is located in the areas above the Keylines.

  Gently sloping country usually exists above the steeper slopes which lie above the Keyline. The valley heads will actually start at the low edge of this flatter country where the steep slope country commences. The High Contour dam is constructed here. The area selected for the dam site can be the side of a hill or ridge. A slope as steep as 1 in 10 is suitable.

  The race or drain to transport water to fill this dam is located above the valley heads. It also serves to protect further these valleys by preventing any flow into them. The drain requires a fall of approximately 5 feet per 1000 feet. The site of the drain and dam must be studied and planned together.

  A sketch and cross section of a High Contour dam built on the steep slope mentioned is illustrated below. Each cubic yard of earth moved conserves two cubic yards of water. This ratio is not as favourable as that in the construction of Keyline and other valley dams which may be round the ratio of six of water to one of excavated material. However, the value of the conserved water in this High Contour dam more than warrants its construction where the topography is suitable.

  The High Contour dam may be constructed anywhere along a ridge where a suitable slope exists and where run-off water can be brought to the dam by a drain from one or both directions.

  Because of these circumstances, the dam is usually long and narrow and always along the contour.

  A bulldozer is used for construction and the earth is moved from the topside straight across the dam to form the wall. In this way the haul is lessened and the cost of earth moving is in direct proportion to the distance the earth is moved, so this distance is kept to the minimum.

  The drain to fill the dam is located and pegged when the dam is marked out. The construction of the dam is completed before the drain is built. There is then no danger whatever of losing from heavy rains any part of the dam during its construction. The back wall of the dam is constructed first. Then the 4-inch pipe outlets are laid at one, or both, ends. After this, the end walls are closed and the drain made.

  A spillway is not constructed, because surplus water is allowed to overflow from the drain at some distance from the dam when it is full.

  It is only necessary to see that the overflow does not occur at the same place more than once during the first year or two, so that no water wash is started. Once the drain is grassed, blocks can be made at any suitable place in the drain to overflow the water there.

  Water transporting drains can become less effective, or sometimes completely ineffective, by becoming overgrown with vegetation. The best means of controlling this growth is by seeding the drain to good grass species and manuring the drain heavier than the adjacent pasture. This encourages the stock to graze the drain area more closely than the rest of the paddock. It is also advantageous to mow regularly the long excavated slope of the drain so that the water transporting capacity of the drain is unimpaired.

  If a road is to traverse the area of the drain it can be placed parallel to and above the drain. The water run-off from the road is caught by the drain and conserved.

  The Keyline dam, constructed on the Keyline, and the High Contour dam, above the Keyline, are the two highest dams used in Keyline planning. For this reason they are the most important dams of all water-conservation schemes.

  The water conserved in these dams is available under pressure for instant use. It is the lowest cost irrigation of all conserved water and is, therefore, used when the first dry spell makes its use profitable and advisable. No dam should ever be completely emptied except for reconstruction or enlargement. A few feet of water is always left in these dams, and this will go a long way toward protecting a bank from dangerous dry cracking.

  There are many farms that do not have their own Keylines. The development of these farms is mentioned in a later chapter. The con servation of water below the Keyline and on these properties of lesser slopes is discussed here.

  The first of these dams is called the Guideline dam, and is, like the Keyline dam, a valley dam. The wall material is excavated from the area of the valley which will be below water level when the dam is filled. All earlier comments about the Keyline dam, including the pipe outlet, are common to this dam. Its particular location is apparent from the chapter "Flatter Lands".

  The next dam in Keyline Planning has its counterpart in the ordinary valley dam. These are to be seen on farms and grazing properties all over the countryside. The main consideration in locating the usual farm valley dam has been to conserve the greatest amount of water for the earth moved.

  With the absorption into the soil and the conservation in Keyline, High Contour and Guideline dams, of practically all the rainfall, a large capacity lower dam has to be located where it can be filled despite these other storages. By locating it in a lower valley, such as the site indicated on Map 4, it is in a favourable position to receive the combined seepages from all the higher country. Apart from seepages, this dam will receive water from very heavy storms and in the periods of general heavy flood rains when most water conservation storages may overflow.

  These dams can be made large to act as a buffer or safety against prolonged drought. They should be as deep as practical, so that evaporation losses are reduced. Losses by evaporation are in proportion to the surface area of the water. A dam six feet deep could lose all its water in a hot dry year, while a deeper dam would lose only the same depth and have water storage when the other is empty.

  The construction of dams by blocking a stream or creek is usually controlled by the Government Water Conservation and Irrigation Authority. Plans for these usually need the approval of this authority, which will also often assist with advice on the preparation of the construction plans.

  Apart from other constructional details, the provision of adequate and safe spillways for overflow is of maximum importance in these stream dams.

  Contour dams, of which the High Contour dam is the one placed in the highest location, can be constructed in almost any type of country to provide low cost large capacity water storage. They are not located in valleys and, as with the High Contour dam, require drains to provide the water.

  On the land below the Keylines they can be filled from a flowing stream or one that flows intermittently.

  The location of a Contour dam is decided by first, the means to fill the dam, and second, a suitable area for the use of the conserved water. The water may be used for spray irrigation and other purposes. The main excavation and bank of the contour dam is always along the contour. The total cross sectional area of the excavation and bank are approximately the same whether the dam is very large or of medium size.

  In the construction of the Contour dam a bulldozer is used and earth is moved straight down the slope at a right angle to the contour. The distance of the "haul" is kept to 100 feet approximately, to provide for the most efficient bulldozer operation.

  A similar construction to that of the High Contour dam is followed. In flatter country the end walls--which are the same length as the width in the High Contour dam--become longer. In the High Contour dam all water is conserved by holding it in the excavated area by the wall. The Contour dam, on the other hand, holds much of its capacity over unexcavated land.

  In flatter country, where the contour dam then assumes the shape of a "broken ring", the end walls are turned in toward each other. The water race feeds the water into the dam between the converging end walls.

  On still flatter sites it assumes the shape of a "complete ring" and the major storage capacity in larger dams is then over the unexcavated central area.

  A pipe outlet is placed through the end wall of the Contour dam at the lowest ground level, and water conserved above this height can be released by gravity.

  Gravity pressure is used for irrigation if the conserved water is high enough.

  The outlet pipe through the wall of these dams can lead directly to a centrifugal pump outside the wall. This maintains the pump under a positive water head, so that instantaneous water pumping is available without pump priming.

  A Complete Ring dam should be constructed on a flat area of land below a ridge to which water can be brought by the drain. In deciding the location of the Complete Ring dam consideration is first given to the filling of the dam by flow from a watercourse. It may be practical to lead water from a watercourse along a water race to a rise close to and above the site, and from this point flow the water over the wall through fluming.

  The filling operation is controlled by a low weir wall constructed across the supply stream bed. A suitable notch outlet is provided to control the water. This wall, constructed of logs, grouted stone or cement, need be only 2 feet to 3 feet high.

  The fluming for the Complete Ring dam may be made of a variety of materials, but its shape is always that of a long trough. Wood or iron fluming is most suitable and the fluming is supported by a trellis of bush timber.

  These dams, ranging from the High Contour to the Complete Ring dam are suitable for easy construction and very profitable use in a wide variety of farming land. Small bulldozers may be used. All the land that can be spray irrigated from such dams will develop rapidly in fertility, productiveness and value. Keyline progressive soil development, greatly stimulated by the correct use of spray irrigation, will bring this land very close to the value class of fertile irrigable river flats.

  The overall costs of spray irrigation will be less than those pertaining to river flats and the pumping of water from the river. River water will have to be "lifted", whereas the water of these dams is at least "assisted" by gravity.