THE IRRIGATION AGE. 



333 



The next best of the cheap means is the canvass 

 dam which is merely a piece of canvass fastened to a 

 staff like a short flag. Laid across a ditch with the 

 ends of the staff on the banks a little earth placed on 

 the edges of the canvass on the bottom and sides of 

 the ditch and tamped a little with a shovel secures it 

 for quite a while, and if the canvass reaches far 

 enough up-stream the downward pressure of the water 

 holds it in place as long as the wateY does not get 

 under it. This dam if well placed lasts longer thaa 

 the iron dam, and can be used to turn a much larger 

 stream. But it cannot be set so quickly or taken up 

 so quickly with the water against it, and when taken 

 up it is heavy and muddy and cannot easily be carried 

 about like the other. It must also be set when the 

 ditch is about dry to make a sure job and if much 

 water is running it cannot be set at all. 



Par better than all else is a permanent gate 

 frame for each check, made of lumber or concrete 

 where cement is cheap, the gate itself being of wood 

 or iron and sliding up and down without hinges. The 

 size, form, and capacity of this will vary so much 

 with soil, crop, head of water, length of time the 



Three feet long is not a bit too much with the gate 

 resting against slanting cleats on the end inside the 

 ditch. When properly set this will need no eddy 

 shields on most soils, nor will it need any apron let 

 into the ground a foot or so to prevent undercutting 

 which will be necessarv in almost any other form of 

 gate frame. But you- may be quite surprised to find 

 it lifted out of place soon after water running past it 

 in the ditch brings a good pressure against it when 

 the gate is closed. This comes from the water getting; 

 underneath it in a sheet and lifting it by hydrostatic 

 pressure from the head in the ditch. It may also be 

 lifted by its own buoyancy when water is flowing 

 through it. In either case a huge muss is apt to be 

 the result. This may be prevented by piling enough 

 earth on it which is easily done because the top should 

 be covered with plank strong [enough to stand if 

 stock should tread on it, and a pile of earth will make 

 it much stronger if heaped in a cone. About the 

 time you have this all fixed and go off and leave it 

 for a while you may return to find it all gone again. 

 It pimply cut out underneath because you did not 

 the bed for it and have it well packed if the 



i Petrified Forest, Arizona. 



water runs as well as your finances that it is useless 

 to give more than a few general hints. 



Your first error may be in making gate frames 

 too short. The eddies cut away the soil at both ends 

 if much water goes through so that little is left on 

 the sides to stand pressure from the ditch. If you 

 put in safe eddy guards, or wings, then they cost just 

 as much as a longer frame. When this is done you may 

 find* the openings are too narrow and not only back 

 up too much of a head of water in the ditch above to 

 leak out through the sides and endanger weak places 

 but increase the pressure on the earth around the gate 

 frame. When you least expect it you may find the 

 water has found its way through in a small stream 

 and pretty soon out it goes. It is better to make it 

 so wide that the height of the water in the ditch is 

 increased very little, with the sill about level with the 

 bottom of the check so that the inflow will not cut out 

 a hole just over the sill by falling. A fall of two 

 inches on some soils will cut out a sill in a short time. 



I find the best form is that of a box. To de- 

 liver four cubic feet a second it should be at least 

 three feet wide and ten inches high and had better 

 be four feet wide to provide against the day when 

 vegetation in the check makes resistance to the flow. 



ground were loose, or it may have cut out the sides 

 because the dirt was not well rammed with the end 

 of the shovel handle. Both are easily prevented by- 

 wrapping the box with old blanket, carpet, quilt, bur- 

 lap, old tent or horse blanket or rag of any kind that 

 is big enough. Water makes a wonderful success of 

 finding a passage between earth and other hard mate- 

 rial and rag is the hardest thing it can find to strug- 

 gle against. If you have old gunny sacks in abun- 

 dance, one about one-third full of earth packed in on 

 each side will make the sides quite safe. Such 

 sacks may be used for the whole thing for temporary 

 work with moderate heads of water as it is almost im- 

 possible for water to pass behind them when well 

 tramped and not filled too full. Three of them in a 

 ditch, one in the bottom and one on each side will 

 pass half a foot or even more of water in safety if the- 

 bottom below is not too mushy, and another placed 

 in the middle makes quite a good dam for some time. 

 With enough of them you can handle quite a large 

 head of water. But if you can afford it an apron of 

 plank a foot wide set in on the bottom and sides is- 

 the purest. And if the soil is mushy it should go in 

 at the lower end and the soil put in dry and be well 

 rammed. 



