Water balance and flow rate discharge on a receiving water body: Application to the B-XII Irrigation District in Spain

•Volumetric model WATEN for hydrological study of a scarce data irrigation district.•Double-mass curve analysis permitted to distinguish data tendencies.•Evapotranspiration was dependant on soil moisture depletion.•Model calibration relied on Solver and Monte Carlo simulations processes.•Drainage, evapotranspiration and soil moisture depletion were quantified.

SummaryThe quantification of the main water balance components becomes necessary to diminish the pollutants load from drainage, and its harmful effect on the environment, aggravated within a context of increasing water scarcity. As a first approach to the hydrological study of the 15,000 ha B-XII Irrigation District in Spain, a conceptual lumped model entitled WATEN has been developed, aiming to calculate the monthly flow rate discharge to the Guadalquivir River over the period 2002-2012. The model requires as inputs, irrigation, precipitation and potential crop evapotranspiration. Main model parameters are the total and readily available moisture in the soil, the effective rainfall and the irrigation efficiency. Energy consumption for drainage discharge was used for calibration. Both classical optimization and a robust approach based on Monte Carlo were performed. In order to diminish computational requirements, Monte Carlo was not haphazardly applied, but conducted on a similar manner to genetic algorithms, entitled Parameters Estimation on Driven Trials (PEDT). The model attained an average Nash-Sutcliffe coefficient e2 ≅ 0.90 between observed and estimated drainage discharge. It was detected a significant crop evapotranspiration reduction compared to potential values. The volume of water discharged to the river might be sufficient for leaching irrigation water salts.