374 



IRRIGATION PRACTICE 



224. Ground water. The seepage losses from reser- 

 voirs, canals, laterals and farms increase the depth of the 

 ground water. Consequently, in irrigated sections, where 

 such losses go on uninterruptedly, water rises slowly but 

 steadily until wells that were dug 50 to 100 feet deep to 

 reach water, now have the water table within 3 to 10 feet 

 from the surface. This great layer of ground water flows 

 along the impervious layer upon which it rests, usually 



fion or we.//s a/on g rru/f A 



FIG. 105. Rise of ground water from irrigation. 



slowly, but sometimes rapidly. Carpenter found in one 

 place that the underground movement of water reached 

 a rate of 1 mile an hour. According to the underground 

 structure of clay deposits, hardpan or bedrock, this water 

 comes out somewhere, usually in the lower-lying lands, to 

 form springs, bogs and water-logged lands. The first 

 irrigation settlements were often made on the lower lands, 

 where the natural seepage made green spots of grass or 

 clumps of trees, that looked inviting to the pioneers. As 

 the higher-lying irrigation canals were taken out, the 

 seepage from them soon converted these green spots, 



