RURAL ENGINEERING. 485 



by hard pumping for some hours and then tapping them with tunnels from the 

 level of the bottom land a few hundred feet away. 



Concrete pipe and overflow basins for distributing irrigation water, E. C. 

 Mills {Engin. Rec, 61 (1913), No. 2J,, pp. 652-65^ figs. 5).— Tests made on 

 1 : 4 gravel concrete pipe, manufactured by the " wet tamp " process, for under- 

 ground distribution of irrigation water in the Sacramento Valley project 

 resulted as follows: Two 18-in. pipes with both ends plugged with concrete and 

 mortar joined, pulled apart at 40 lbs. pressure without injury to the pipe; 2 

 18-in. pipes, similarly joined and so placed as to prevent longitudinal rupture, 

 withstood an intei'nal pressure of 35 lbs. for 1 hour and broke at 60 lbs. 

 pressure; a 16-in. pipe similarly arranged broke at 55 lbs. and a 10-in. pipe at 

 70 lbs. pressure. 



Two general sj-stems of underground distribution, both of which gave satis- 

 faction on this project, are the open or overflow system, adapted to hillside 

 planting, and the closed or pressure system, adapted for use whei-e an artificial 

 heiid is required for proper distribution. In either system the water is delivered 

 to the main pipe through a measuring box equipped with a measuring weir, and 

 to the branch lines through similar measuring boxes placed at points of diver- 

 sion from the main line. Since the allowable head on unreenforced pipe lines 

 is taken not to exceed 10 ft., concrete overflow basins or standpipes of proper 

 height are placed at intervals to relieve the line of any excessive pressure. 

 These overflow basins are also conveniently arranged for irrigation and are 

 equipped with vertical slide gates to regulate the flow. 



It was found that pipe to withstand more than 10 ft. head or to be placed 

 under more than 4 ft. of backfill, or both, should be reenforced, or have extra- 

 heavy cement joint collars, or both. At the top of every rise in the line air 

 valves should tje installed to relieve the air pressure and to prevent water ham- 

 mer when the line is being filled. 



The approximate cost per foot of concrete pipe lines in the Sacramento Valley 

 including trenching and backfilling was from $0.28 to $1.55 for pipes of sizes 

 varying between 8 and 36 in. 



Convoluted tube wells for irrig-ation, T. A. M. Brownlie (Agr. Jour. India, 

 8 (1913), No. 2, pp. I.'f5-156, figs. 2). — From his own and other experiments 

 the author concludes that drawing water from the ordinary type of well for any 

 length of time, at a rate exceeding the critical velocity of the subsoil below 

 the well, results in silting and in a loosening of the subsoil, causing the well 

 to sink and collapse. This critical velocity has been found to be between 2i 

 and 3 ft. per hour. 



Experiments conducted with tube wells of various forms in several conditions 

 of subsoil, natural and artificial, resulted in a conclusion that water may be 

 withdrawn constantly from these tubes at a rate which represents the velocity 

 through the waterway area of the strainer of from 40 to 60 times the critical 

 velocity of the subsoil. For domestic purposes the so-called Abyssinian tube 

 well is suggested, and for irrigation and other purpose requiring heavier pump- 

 ing the convoluted tube well. 



Data from service tests of 40 wells equipped for irrigation and operated by 

 bullock power indicate that the average plant costing a total of about 1,300 

 rupees (about $421) will pump 2,400 gal. per hour at a cost of 1 anna (about 

 2 cts.) for 1,305 gal. Data from service tests of sevei-al wells with the equip- 

 ment driven by steam or oil engines indicate that the average plant costing 

 ;;bout 6,000 rupees (.'?1,944) will pump about 25 000 gal. per hour at a cost of 1 

 anna for 1,800 gal., showing an increase of practically 40 per cent over bullock 

 power. 



