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Keyline design is a technique for maximizing beneficial use of water resources of a piece of land. The Keyline refers to a specific topographic feature linked to water flow. Beyond that however, Keyline can be seen as a collection of design principles, techniques and systems for development of rural and urban landscapes. Keyline design was developed in Australia by farmer and engineer P. A. Yeomans, and described and explained in his books The Keyline Plan, The Challenge of Landscape, Water For Every Farm and The City Forest.
P. A. Yeomans published the first book on Keyline in 1954. Yeomans described a system of amplified contour ripping to control rainfall run off and enable fast flood irrigation of undulating land without the need for terracing.
Keyline Designs include irrigation dams equipped with through-the-wall Lockpipe systems to gravity feed irrigation, stock water and yard water. Graded earth channels may be interlinked to broaden the catchment areas of high dams, conserve the height of water and transfer rainfall run-off into the most efficient high dam sites. Roads follow both ridge lines and water channels to provide easier movement across the land. 
Keyline Scale of Permanence 
The Keyline Scale of Permanence identifies typical farms elements ordered according to their degree of permanence. Keyline considers these elements when planning the placement of water storage, roads, trees, buildings and fences. On undulating land, a keyline approach involves identifying several features namely ridges and valleys and the natural water courses seeking optimum water storage sites and potential interconnecting channels.
The water lines identified from the land-form subsequent provide optimal locations for the various less permanent elements (roads, trees, buildings and fences) to optimise the natural potential of the landscape.
In a smooth grassy valley, a location called the Keypoint can be found where the lower and flatter portion of a primary valley floor suddenly steepens. The — Keyline — of this primary valley is revealed by pegging a contour line through the keypoint, within the valley shape. All the points on the line are at the same elevation as the keypoint. Contour plowing parallel to the Keyline, both above and below will automatically become "off-contour" but the developing pattern will tend to drift rainwater runoff away from the valley centre and incidentally, prevent erosion. Keyline pattern cultivation on ridge shapes is done parallel to any suitable contour but only working on the upper side of the contour guide line. This automatically develops a pattern of off-contour cultivation in which all the rip marks left in the soil will slope down towards the centre of the ridge shape. This pattern of cultivation allows more time for water to soak in. Keyline pattern cultivation also enables controlled flood irrigation of undulating land, which further assists in the fast development of deep biologically fertile soil, which results in improving soil nutrition and health.
In many countries including Australia, it is important to get optimum absorption of rainfall and Keyline cultivation does this as well as delaying the potentially damaging concentration of runoff. The Yeomans technique differs from traditional contour plowing in several important respects. Random contour plowing also becomes off contour but usually with the opposite effect on runoff water causing it to quickly shed off ridge shapes and be concentrated in valleys. The limitations of the traditional system of soil conservation, with its "safe disposal" approach to farm water was an important motivational factor in the development of the Keyline system.
David Holmgren, one of the founders of Permaculture, used Yeoman's Keyline principle extensively in the formulation of Permaculture concepts and the design of sustainable human settlements and organic farms.
Keyline also includes concepts for rapid soil fertility enhancement and these concepts are explored in Priority One by P. A. Yeomans' son Allan. Yeomans and his sons were also instrumental in the design and production of special plows and cultivating equipment for use in conjunction with the keyline methodology.
See also 
- Yeomans, P.A. (1954). The Keyline Plan (Free online). OCLC 21106239.
- Yeomans, P.A. (1958). The Challenge of Landscape : the development and practice of keyline (Free online). Sydney NSW: Keyline. OCLC 10466838.
- Yeomans, P.A. (1973). Water for Every Farm: A practical irrigation plan for every Australian property. Sydney NSW: K.G. Murray. ISBN 0-646-12954-6. ISBN 0-909325-29-4.
- Yeomans, P.A. (1971). The City Forest (Free online). Keyline. ISBN 0-9599578-0-4. OCLC 515050.
- Yeomans, P.A.; Yeomans, K.B. (1993). Water for Every Farm — Yeomans Keyline Plan. Keyline Designs. ISBN 0646129546. 2002 ISBN 0646418750
- Yeomans, P.A.; Yeomans, K.B. (2008). Water for Every Farm — Yeomans Keyline Plan. Keyline Designs. ISBN 1438225784.
- Yeomans, A. (2005). Priority One: Together we Can Beat Global Warming (Online). Keyline. ISBN 0-646-43805-0.
- MacDonald-Holmes, J. "Geographical and Topographical Basis of Keyline".
- Spencer, L (2006). "Keyline and Fertile Futures".