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 dram 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 

 4to ^^^ iw^-rr^ s^rAc^ . impervious hard-pan or sub- 









Cl/vy. 









^^ 



SAf^a W' 



'5 



*;^— 6" 



.5^11 



Clav 



; Til. ft 





•v-SAMC^ 



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 

 adjacentstreamsorotherdrain- 

 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 m a number of the Euro- 

 pean countries, is but Httle 

 developed mthe United States. 

 One of the most interesting 

 pumping drainage projects 

 known is the great Haarlem 

 Lake of Holland. Until 1852, 

 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. 



IHRIGATION 



Irrigation Is the Artificial Watering ot Land.— It is the opposite 

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



Fig 62 — A vertical dram A porous or 

 gravelly stratum should underlie the impervi- 

 ous hard-pan or subsoil and the water must 

 have a chance to flow away (Wis Station ) 



