I. Customary methods of mole drains
The arrangement of mole drains is different from region in Japan. In southern districts, the depth, distance, length and drainage area are smaller than in northern districts.
The execution techniques of main drains and junction boxes are well developed in south-west districts, particulary in Kyusyu, and in Hokkaido (Table 1).
II. Field experiments on method of execution
(1) When the drains are deep, silt is accumulated at the bottom of mole drains, and the durability of drain hole is very low (Tables 2, 3).
(2) When the drains are steep, very little silt is accumulated (Table 4).
(3) When the distance of drains is small, the groundwater level goes up or down speedily and uniformly (Tables 5, 6, 7).
(4) The water content (%) of both surface soil and subsoil in the operated is smaller in drained field than in undrained field ; with tile drains than with mole drains ; and with smaller distances than with larger distances. The hardness of soil has a reversed relation with the distance of mole drains (Tables 8, 9).
(5) In the humid season of spring, the rate of drainage is larger with drains of smaller distances than with drains of larger distances (Table 10).
(6) The growth and yield of rice after execution are higher with smaller distances than with larger distances (Table 11).
III. Future aspects of mole drainage
Mole drains have following two coming ways performed in future.
(1) Function of soil improvement (as regulators of soil moisture in the field).
Mole drains are to be adopted in farming procedures as artificial and three-dimentional regulators of soil moisture. The function is similar to that of subirrigation or subdrainage. In this case, as mole drains may be reconstructed each year or every few years, the durability of drain holes is not important problem, but their execution procedures must be simplified.
(2) Mechanical construction of underdrains (as a device for land improvement).
For example, liquid concrete drains and continuously formed concrete tube for drainage are suggested. The tendency is toward the adoption of the former method in Japan. The latter method, too, must be of a great importance in future.

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