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A great number of flood irrigation districts which have low irrigation efficiency due to the high permeability of their soils cannot undertake a generalised changeover to pressurized irrigation systems in the short term. This work seeks to study the effects which the changeover of the irrigation system in the Irrigation District Nº V of Bardenas (Spain) would have on the hydric regime of the Miralbueno aquifer; also to evaluate different alternatives to improve water management based on the use of groundwater. For this, a model of the aquifer was made with the help of the Modflow 2000 software and different scenarios were simulated. The results indicate that generalised conversion to pressurized irrigation systems will cause a decrease in the average phreatic level (1.20 m) and in the volume of water drained by the ditches (49% less). Until this measure is taken, the irrigation efficiency of the agrarian system could be increased notably by intensifying the reuse of groundwater by means of: a) the construction of intercepting drainages to reuse groundwater in flood irrigation again, and b) the construction of appropriately distributed wells for drip irrigation of the current area of vegetables.