page_title: Hydrology (agriculture)
section_title: Irrigation and drainage requirements
hierarchical_section_title: Hydrology (agriculture) / Irrigation and drainage requirements
caption_attribution_description: English: Rainfall, evaporation, water storage and drainage requirement in the Netherlands
context_page_description: Agricultural hydrology is the study of water balance components intervening in agricultural water management, especially in irrigation and drainage.
context_section_description: The irrigation requirement (Irr) can be calculated from the topsoil water balance, the agronomic water balance or the overall water balance, as defined in the section "Combined balances", depending on the availability of data on the water balance components. 
  
  Considering surface irrigation, assuming the evaporation of surface water is negligibly small (Eva = 0), setting the actual evapotranspiration Era equal to the potential evapotranspiration (Epo) so that Era = Epo and setting the surface inflow Isu equal to Irr so that Isu = Irr, the balances give respectively:
  Irr = Epo + Osu + Per − Rai − Cap
  Irr = Epo + Osu + Dtr + Dgw − Rai − Lca − Ugw
  Irr = Epo + Osu + Dtr + Oaq − Rai − Lca − Iaq
  Defining the irrigation efficiency as IEFF = Epo/Irr, i.e. the fraction of the irrigation water that is consumed by the crop, it is found respectively that :
  IEFF = 1 − (Osu + Per − Rai − Cap) / Irr
  IEFF = 1 − (Osu + Dtr + Dgw − Rai − Lca − Ugw) / Irr
  IEFF = 1 − (Osu + Dtr + Oaq − Rai − Lca − Iaq) / Irr
  Likewise the safe yield of wells, extracting water from the aquifer without overexploitation, can be determined using the geohydrologic water balance or the overall water balance, as defined in the section "Combined balances", depending on the availability of data on the water balance components.
  Similarly, the subsurface drainage requirement can be found from the drain discharge (Dtr) in the subsoil water balance, the agronomic water balance, the geohydrologic water balance or the overall water balance.
  In the same fashion, the well drainage requirement can be found from well discharge (Wel) in the geohydrologic water balance or the overall water balance.
  The subsurface drainage requirement and well drainage requirement play an important role in the design of agricultural drainage systems (references:, ).
caption: Average climatic data and drainage in the Netherlands
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