Using the depleted fraction to manage the groundwater table in irrigated areas

M.G. Bos, W.G.M. Bastiaanssen

Research output: Contribution to conferenceConference paperAcademic


The depleted fraction, defined as the ratio of ETactual over (P + Vc ), relates parameters of the water balance of an irrigated area with each other in such a way that the (water) manager obtains information on the rate of change of water stored in the area (soil moisture and groundwater). If the depleted fraction equals about 0.6 water storage in the area is stable, while water is stored for lower values of the depleted fraction. If the value of the depleted fraction exceeds 0.6, the volume of water stored in the area decreases. Part of this decrease is due to natural drainage and part due to capillary rise into the root zone of the irrigated crop. Despite this capillary rise the actual evapo-transpiration drops below the potential ET-value. For most crops, a decrease of ET by about 15% would result to a higher productivity in terms of yield per cubic meter water. However, the yield per hectare (and thus farm income) would decrease. Management of an irrigation system is recommended in such a way that the monthly values of the depleted fraction range between 0.5 and 0.8. Such a management rule would provide sufficient water for leaching (at the 0.5 side of the range) and provide high crop yield per unit water consumed (at the 0.8 side).
Original languageEnglish
Publication statusPublished - 2003


  • irrigation
  • soil water
  • water table
  • evapotranspiration
  • drainage
  • models
  • arid zones


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