SummaryThe physics of land drainage is developed from the application of Darey's law to the water movement produced as a result of the conditions at the boundaries of the groundwater region in a given drainage situation. The physical understanding of the groundwater problem so obtained allows land drainage to be considered as an engineering operation founded on rational scientific principles and allows recommendations to be made concerning the design of installations. However, for theory to be applied in many field situations, a greater understanding of the soil‐water physics of heterogeneous soils, of fissured soils and of swelling soils is require