126 



LAND DRAINAGE AND IRRIGATION 



the surface even more water. The successful ones never fill, no 

 matter how much water may drain into them. 



The most common vertical drains consist of ordinary drain tile 

 placed in the ground vertically, end on end (Fig. 62). It should 

 be remembered that the only conditions under which such a drain 

 can work are : first, a porous or gravelly stratum should underlie the 



impervious hard-pan or sub- 

 soil ; and, second, that stratum 

 should be dry so that the drain- 

 age water may flow away. 



Drainage by Means of 

 Pumps. The drainage of 

 many low-lying lands is made 

 possible only through the use of 

 pumping machinery to lift the 

 drainage water over levees into 

 adjacent streams or other drain- 

 age channels. The drainage of 

 such areas is done by open 

 ditches and tile but all the 

 drainage water discharges into 

 reservoirs, and from them it is 

 pumped over the levees. This 

 kind of drainage, though suc- 

 cessful in a number of the Euro- 

 pean countries, is but little 



developed in the United States. 

 One of the most interesting 



FIG. 62. A vertical drain. A porous or pumping drainage projects 

 gravelly stratum should underlie the impervi- .-, j TT i 



ous hard-pan or subsoil, and the water must known IS the great Haarlem 



have a chance to flow away. (Wis. Station.) Lake Q Holland Until 1852j 



this lake was fifteen feet deep and covered about sixty-five square 

 miles. Now this area, formerly a lake, is traversed by well- 

 improved highways and is occupied by about 20,000 people. In a 

 similar manner the Dutch Government (1913) authorized the 

 undertaking of the complete reclamation of about 781 square 

 miles of what is now the southerly portion of the Zuider Zee. 



IRRIGATION 



Irrigation Is the Artificial Watering of Land. It is the opposite 

 of land drainage. Irrigation is commonly thought of as a practice 



