GROUND WATER, WELLS AND FARM 

 DRAINAGE. 



CHAPTER XII. 

 MOVEMENTS OF GROUND WATER. 



Of the water which falls upon the land one portion finds 

 its way at once, by surface flow, into drainage channels; a 

 second portion is evaporated where it fell, while a third 

 enters the ground. That portion which enters the ground 

 and is not returned by capillarity or root action constitutes 

 the body of ground water which is the source of supply for 

 wells and springs and which requires removal by land 

 drainage when too close to the surface. 



322. Amount of Water Stored in the Ground. In most 

 localities after passing a certain distance below the earth's 

 surface a horizon is reached where the pore space in the 

 soil, sand and rock is filled with water or nearly so. When 

 these pore spaces are large, so that water can flow through 

 them readily, wells sunk beneath the surface fill with water 

 to the level of the ground water surface. 



In sands and sandstones lying below drainage outlets 

 the amount of water may be as high as 15 to 38 per cent, 

 of the total volume of the rock so that where a country is 

 underlaid with broad and thick sheets of sandstone, such 

 as the Potsdam and St. Peters in Wisconsin and further 

 south, or the Dakota formation in the west, there is the 

 equivalent of from 15 to 38 feet of water on the level for 

 every 100 feet in thickness of the rock formation, and 



