880 



THE IKK I G ATI OX AGE. 



(Continued from page 859.) 



of the structure, on the principle of the well-known "gravity'' 

 type of dam. 



Dams to be constructed on alluvial foundations should 

 be designed with the maximum width of base which is con- 

 sistent with economy ; therefore, the gravity type of dam, 

 constructed of reinforced concrete, is especially adapted to 

 the requirements. 



In low wooden structures of the gravity type there is 

 danger that they may float during a period of storm-flow 

 of such depth that the gravity head, on which such dams de- 

 pend for their stability, may be destroyed. By the use of 



reinforced concrete, however, this source of danger may be 

 eliminated. 



Figure 3 and 4 indicate two variations of design for 

 gravity dams of reinforced concrete which permit of re- 

 moving the forms and filling the compartments with sand 

 or other heavy material, in order to give additional weight 

 to the structures, or, if suitable air vents are provided, the 

 compartments may be allowed to become filled with water. 



From the simple inclined platform to the large hollow 

 structures of the Ambursen type, the gravity dam of rein- 

 forced concrete offers a sufficiently wide range of variation 

 to meet the requirements of almost any locality, or any 

 individuality of taste in engineering design. 



Table I. Velocity of flow of water, in feet per day in 

 Massachusetts State Board of Health. 



Effective 

 10 

 246 

 475 

 902 

 1,700 

 3,250 

 2,780 

 3,150 



screened gravel, ' assuming 40 per cent porosity, based on experiments of the 



Slope, s. 



0.0005 



0.001 



0.002 



0.004 



0.006 



0.008 



0.01 



57 

 115 

 '221 

 386 

 443 

 549 



82 



172 



328 



631 



918 



1,160 



1,410 



164 



335 



639 



1,230 



1,690 



2,060 



2,460 



Sizes, 

 15 

 410 

 820 

 1,550 

 2,870 

 3,690 

 4,340 

 5,000 



in Millimeters.- 

 20 

 656 

 1,210 

 2,250 

 3.930 

 5,080 

 5,900 

 6,SOO 



902 



1,680 

 3,030 

 5,000 

 6,390 

 7,380 

 8.440 



30 



1,280 

 2,250 

 3,930 

 6,060 

 7,620 

 8,930 

 10,000 



35 



1,640 



3,030 



4,830 



7,130 



8,930 



10,400 



11,500 



40 



2,050 



3,690 



5,820 



8,200 



10,100 



11,800 



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IRRIGATION DITCHER 



When writing to advertisers please 



Making a V bottom ditch two feet deep. 



This same machine will make Laterals, 

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mention The Irrigation Age. 



