70 LAND DRAINAGE 



impervious strata of clay subsoil. These* areas are fre- 

 quently well up on the sides of slopes, and not infrequently 

 on the top of the highest parts of fields. Such areas 

 may comprise but a few square rods, and yet so persistently 

 is the water held that planting is delayed and, in some 

 cases, actually prevented. Such areas are very common 

 in glacial formations. 



, 5. Springy places that occur at the foot of slopes and 

 not infrequently high up on the sides of slopes. 



100. Methods of drainage. The method to be em- 

 ployed in removing surface water will depend on a number 

 of things, such as: (1) the area to be drained; (2) the 

 nature of the soil ; (3) topography ; (4) the natural 

 facilities for outlet ; and (5) cost of labor and material. 



Three methods of drainage are common. They are 

 open ditching, shallow surface drainage and tile drainage, 

 to which may be added a fourth, the use of wells. The 

 latter is sometimes employed in connection with tile 

 draining. 



101. Open ditches. Open ditches are employed in 

 extensive flat countries where the amount of water to be 

 removed is large, and where the fall is slight. In such 

 cases the ditches are often of considerable width and 

 depth, and the nature of the work in laying out and 

 developing such drainage systems is such as to require 

 the training and direction of a professional engineer. 

 After the main ditches have been completed in such sys- 

 tems, it is possible to use tile drainage in the smaller units. 



102. Shallow open ditches. The shallow, open, or 

 surface ditch is employed where the soil is so impervious 

 as to prevent the ready passage of the water downward to 

 drains laid at ordinary depths in tiling, or where natural 

 or artificial outlets cannot be had, or in new sections of 



