LAUSR

Abstract Shallow aquifers significantly impact crop growth as saturated soil conditions may occur. Canals are widely constructed in such areas to mitigate groundwater saturation or flooding. We applied a simulation model to estimate the occurrence of root zone saturation [root zone saturation index (RZSI)] for agricultural crops and to identify factors that influence root zone saturation in a shallow coastal aquifer and canal system. Results indicated that groundwater modeling combined with multiple linear regression can relate the influencing factors and root zone saturation durations in low lying farmland adjacent to canal systems. In our study, most areas had a low RZSI, but areas towards the northwest and southeast where the land surface elevation is generally low were predicted to have a greater RZSI. In general, positive correlations were found between the root zone saturation durations and rainfall amount, antecedent groundwater table elevation and average canal stages in areas where the higher RZSIs were predicted. Rainfall amount played a more important role than antecedent groundwater table elevation and canal stage in determining the root zone saturation during the wet season, while antecedent groundwater table elevation and canal stage played a more important role than rainfall amount during dry season. Correlations between the predicted root zone saturation duration and land surface elevation were negative and stronger during the wet season than the dry season, and the correlations were stronger in the deep (0–61 cm) root zone than with the shallow (0–18 cm) root zone. In area where the land surface elevation is relatively high, the root zone saturation duration was not influenced by rainfall amount, antecedent groundwater table elevation or canal stage, at least under the current management practices and climate conditions.