In irrigated agriculture, water normally has to be conveyed from a source (river, lake, reservoir, well) to the field, eighter by canals or by pipes. Depending on the condition of the infrastructure, the length of the canals and the climate, there are during the transport in the canal system: percolation into the ground, seepage through the canal bunds, spilling over the bunds and through holes in the bunds, uptake by weeds on the bunds or banks and evaporation from the water surface. A decisive factor regarding losses is the material of the canals. In earthen canals, losses are higher than in lined canals. In lined canals, losses depend on the condition of the lining.
The losses can be estimated and/or measured and allow to assess the conveyance efficiency (ec) in percent. According to FAO between 60 - 95 % conveyance efficiencies (see Table 1) and 60 - 90 % field application efficiencies apply (Table 1).
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Earthen canals
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Lined canals
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Soil type
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Sand
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Loam
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Clay
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Canal length
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Long (>2000 m)
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60 %
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70 %
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80 %
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95 %
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Medium (200 - 2.000 m)
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70 %
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75 %
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85 %
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95 %
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Short(< 200 m)
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80 %
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85 %
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90 %
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95 %
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Table 1: Indicative values of conveyance efficiencies for adequately maintained canals[1]
Water losses on-farm or on the field are caused by deep percolation to soil layers below the crop root zone, by surface run-off, by use of weeds and by evaporation from the soil surface between the crops. Another important factor is the farmer’s training and knowledge with regard to agriculture and irrigation.
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Irrigation method
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Field application efficiency
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Surface irrigation (border, furrow, basin)
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60 %
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Sprinkler irrigation
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75 %
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Drip irrigation
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90 %
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Table 2: Indicative values of field application efficiencies[1]
References
- ↑ 1.0 1.1 FAO (1989): Irrigation Water Management: Irrigation Scheduling. http://www.fao.org/docrep/T7202E/t7202e08.htm#annex%20i:%20irrigation%20efficienciesfckLR[accessed 19 April 2013]
GIZ (1993): Irrigation and the environment - A review of environmental issues. Part II: Environmental considerations in planning and operations.
