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IOWA DEPARTMENT OF AGRICULTURE. 



time to damage the road. It is just as economical, and far more prac- 

 tical, for the road builder to put in four or five 12-inch culverts at such 

 points as may be found necessary in a mile of roadway as it is to carry 

 water along the higher side of the road a mile or more and be com- 

 pelled to deliver it in a 24-inch culvert. 



LAYING CULVERT PIPES.— In the laying of culvert pipes or box 

 drains the upper end or intake should be kept sufficiently high to insure 

 a proper flow of the water. The excavations for culvert pipes should 

 be straight and of uniform grade, so as to provide a regular, even fall 

 from the upper to the lower side of the road. Earth should be carefully 

 tamped around such pipes and they should be placed at sufficient depth 

 to prevent their being broken by the traffic. In order to protect pipe 

 culverts from damage when discharging water under full pressure it is 

 desirable that the joints be cemented and that the ends of tne culvert be 

 protected with masonry. (Pig. 6.) Under no circumstances should a 



Fig. 6. — Culvert pipe with ends protected by masonry. 



ridge over the culvert pipe be allowed; for it not only endangers the 

 life of the culvert, but is a menace to traffic. 



SIZE OF CULVERT PIPES.— In determining the size of the culvert 

 pipe it is necessary to consider the area to be drained as well as the 

 maximum rainfall. One inch of rainfall per hour gives about 22,000 gal- 

 lons of water for each acre, and it is probably true that only about one- 

 half of this amount ordinarily reaches the culvert within the same hour. 

 This fact should also be considered in determining the size of pipe or 

 culvert required. The following table shows the capacity of round vitri- 

 fied clay pipes ordinarily used for culverts: 



SIZES OF DRAINPIPE REQUIRED FOR CULVERTS IN PROPORTION TO 

 CAPACITY AND FALL. 



It will be seen from the above table that as the fall increases the 

 capacity of the pipe is increased in proportion. Observing this princi- 

 ple, it is often possible to decrease the size of the pipe and by so doing 



