A number of theories for tile and ditch drainage have been proposed in recent years which, if valid, would enable the rational design of many drainage systems. Nevertheless, most drainage systems are still designed by rule of thumb based largely upon the observations of technicians with experience in certain restricted areas.

To develop a theoretically sound and practically valuable method of designing subsurface drainage systems, the various approaches which have been made should be critically evaluated and compared, mutually, as well as with field data. However, no such analysis has been found in the literature.

The object of this publication is to provide this type of appraisal. The assumptions underlying a number of methods of analysis will be scrutinized in detail, and various applications of these methods to field results will be tested. It is hoped that this evaluation of the status quo will be useful in determining to what extent present theories lend themselves to field applications and what phases of drainage design need further study.

In general, this discussion will be restricted to problems of saturated flow, while recognizing that flow in the unsaturated zone above the water table often may be important. Little progress has been made in formulating quantitative theories regarding flow in the unsaturated zone.