FIELD-SCALE DISTRIBUTED MODELING OF BYPASS FLOW IN A HEAVILY TEXTURED CLAY SOIL

Water transport in structured soils is influenced strongly by macropores. This study developed a water transport model to simulate bypass flow processes on the field scale. The LEACHW-model was extended with subroutines describing bypass flow, tortuous water transport through macropores and absorption of water along macropore walls. The model was tested on measurements from an experimental site in the Netherlands. A Monte-Carlo analysis in combination with a Rotated-Random-Scan procedure took variability of model parameters into account and, subsequently, calibrated the model. A sensitivity analysis showed that the conductivities of the top soil layers were the most sensitive parameters in the model. Validation of the model on independent data showed that the model is capable of simulating bypass flow realistically. The Rotated-Random-Scan procedure is a valuable tool for the quantification of ill-defined model parameters.