Simulating unsteady soil evaporation under variable water content based on Campbell's two-parameter retension model

Subject Areas : Farm water management with the aim of improving irrigation management indicators

Raziyeh Aghajani ¹ , Mehdi Homaee ² , Mohammad Bybordi ³

1 - M.Sc. Student, Department of Soil Science, Tarbiat Modares University, Tehran 14115-336, Iran
2 - Professor, Department of Soil Science, Tarbiat Modares University, Tehran 14115-336, Iran
3 - Professor, Department of Soil Science, Tarbiat Modares University, Tehran 14115-336, Iran

Received: 2012-02-05 Accepted : 2012-04-20 Published : 2012-09-02

Keywords: Campbell’s model, unsteady evaporation, water table,

Abstract :

Large areas in Iran are located in arid and semi-arid regions and imposed to serious water shortage. In such areas, not only the available water resources are restricted, but the climatic conditions that are influencing evaporation acting more intensively. The objective of this study was to estimate evaporation from bare soil at presence and absence of impervious layer, water table and free drainage. The amount of evaporation is also estimated using the parametric model proposed by Zarei et al., (2009) based on Campbell’s retention model. For this purpose, some PVC constructed lysimeters were filled with soil samples and packed carefully. The amount of evaporation was measured three times a day by weighting the lysimeters. The proposed model of Zarei et al.,(2009) based on Campbell’s retention model was further verified against the collected experimental data to estimate evaporation from water table drawdown. Model verification indicated that the maximum (98.8) and minimum (84.8) efficiencies belong to 150 and 75 centimeters of water table depths, respectively. The results, with slightly underestimation, indicated a reasonable agreement between the measured and model output data. The small underestimation between measured and predicted values can be attributed to moisture loss as vapor, soil shrinkage and errors in digital scale measurements. The predicted instantaneous evaporation values provided better agreement with the experimental data as the water table depths were increased.