IRRIGATION AND DRAINAGE 151 



name (Fig. 98). For each inch of height the sides slope 

 back J4: inch on each side. That is, if the height is 8 inches, 

 and if the width at the bottom 20 inches, then the width at 

 the top will be 20 plus 2 plus 2 equals 24 inches. 



Certain precautions are necessary in the construction of 

 this weir. The distance from the crest of the weir to the 

 bottom of the canal or floor of the weir box should be at 

 least three times the depth of water flowing over the weir. 

 The bottom and sides of the weir notch should be beveled 

 on the downstream side to give a narrow edge. Water 

 should approach the weir with a velocity not greater than six 

 inches a second. The water passing over the weir should have 

 a free overfall. An ample distance must be left between the 

 ends of the weir crest and the sides of the ditch or weir box. 



247. Water rights. In almost all agricultural localities 

 water is scarce some of the time; and in the arid parts of 

 the country it is deficient all the time. It is, therefore, 

 valuable to the user, and to protect him and assure him of 

 undisputed right to his fair share, the law-making bodies of 

 the several states have drawn up an elaborate code of water 

 rights. These are in many cases of very great value, exceed- 

 ing that of the land itself. They depend to some extent on 

 priority of claim. "First come, first served" is the principle 

 on which such rights are based. But there is a growing 

 tendency in America to base the right to water on the use 

 of it. Water, according to this view, is a natural resource 

 the ownership of which is given over to those who will 

 render in return the largest service to society. 



Riparian rights, recognized in some states but not in 

 others, are based on a different principle; that is, on the 

 assumption that the farms touching the streams have a 

 prior right to the water. Such rights have given rise to many 

 forms of injustice and are difficult of legal supervision. 



The entire matter of water right legislation is growing 

 increasingly complex and important; for as the demand 



