Characteristic Trend in Surface Undulations of Paddy Fields with Remarkably Poor Surface Drainage

The authors created multiple computer-based models of paddy fields with surface undulations that do not deviate from reality, and conducted simulations of their surface drainage. The results are summarized as follows: i) there are certainly paddy fields which demonstrate remarkably poor surface drainage, ii) main cause of the remarkably poor surface drainage in those paddy fields is the fact that protruding parts (hardly appearing in the leveling accuracy) which block the water flow exist within the narrow area in the vicinity of each outlet, iii) merely constructing just one open ditch along the drain in such a paddy field is enough realize a significant drainage improvement.