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THE IRRIGATION AGE. 



SIMPLE EARTHERX DAMS. 



BY SAMUEL FORTIER. 

 II 



In some instances the water is pumped by an 

 engine through a system of piping and the water is 

 applied by lines of hose with nozzles attached. As- 

 suming that water can be brought by gravity, per- 

 haps the cheapest and most effective method is as 

 follows: 



Allow water to run into the trench named above 

 until full, then begin to form the base of the embank- 

 ments. As the contents of the scrapers, carts or 

 wagons are dumped on the fill, have them thoroughly 

 sprinkled by an ordinary street sprinkling wagon. If 

 such is not available, a good substitute may be made 

 out of a large barrel or redwood plank box with a 

 piece of perforated pipe for a sprinkler, controlled by 

 a hinged flap valve faced with leather. 



If the material is still too dry to pack well, it is 

 advisable to sprinkle or wet in someway the material 

 before taken from the pit. As the fill rises more 

 water is turned into the trench so that the whole base 

 presents an appearance of two low, wide embank- 

 ments, with a canal full of water between. The 

 better way, theoretically, would be to allow both 

 halves of the base to slope up stream, but it is some- 

 what difficult to do this in practice and the plan fol- 

 lowed by the writer has been to allow both slides to 

 slope towards the canal in the center. By so doing 

 the material is readily crowded into the water and the 

 outer edges being highest, the whole top can be flooded 

 if necessary, when the teams are not working. The 

 sketch showing cross section in partially completed 

 embankment will illustrate the method. 

 In one reservoir built under the superintendence of 

 the writer there was a shrinkage in material at the 

 time of building of twenty-seven per cent. In other 

 words, every cubic yard excavated after being moist- 

 ened and packed did riot make quite three-fourths of 

 a yard in the fill . 



By building in water in the center one secures 

 practically the same results as with a core of puddled 

 clay, concrete or masonry, without the serious disad- 

 vantage of a joint on each side of such a core, which 

 often proves fatal to the structure. By the other way 

 there are no distinct joints, since the water in the 

 canal percolates quite a distance on each side, and 

 then these half embankments are watered by a 

 sprinkler and packed by the passage of the teams 

 into a mass nearly as compact as that done under 

 water. 



Another suggestion to those inexperienced in such 

 work may be made, in relation to the sorting of the 

 materials. In nearly every case in practice the con- 

 tents of the bank or pit differ, running from fine to 



coarse and from porous to impervious, and success- 

 ful practice requires the placing of that which is the 

 best adapted to retain water next to the edge of the 

 water, or on the inner half, while the rocks, larger 

 gravel and heavy substances in general are ranged 

 from the outside towards the center on the outer half. 

 In contract work it is well to have a man where exca- 

 vation is made who shall direct where each team 

 shall unload, thus securing a staple and at the same 

 time an impervious bank. In distributing reservoirs 

 for city systems the slopes are made comparatively 

 steep, say from 1% horizontal to 1 vertical, up to 2^ 

 to 1, since the outer slope is usually seeded down to 

 grass to prevent wash, while the inner slope is paved 

 with brick, cement concrete, asphalt or stone. In 

 storing water for irrigation it is advisable to make 

 the slopes, particularly the inner one, more flat and to 

 protect it where it is liable to wash by riprapping 

 with rock or slag, or lining with lumber. 



Notwithstanding all these precautions, if there is 

 not sufficient space for the water, in great floods, to 

 escape other than over the top of the dam, a wash- 

 out is inevitable. In many proposed sites a narrow 

 rocky ridge can be blasted off down to a level of the 

 surface of the water in the reservoir when full. In 

 other sites an earthen bank may be excavated down 

 to a similar level, and the surplus water wasted 



-j, 



through a short, wide canal made for that purpose, hav- 

 ing as steppe a grade as the nature of the earth will 

 permit. If the material is not suitable a flume of some 

 kind will answer all requirements, and in deciding 

 upon its area it is well to figure up the total maxi- 

 mum flow of surplus water which is ever likely to 

 pass through this flume, and then to make it as large 

 again as such a volume requires. 



SOMETHING ABOUT ALKALI. 



Some farmers in alkali districts believe that the 

 alkali observed in their soils, and which often pre- 

 vents the growth of crops, is the result of an excess 

 of potash in the soil. This, unfortunately, is not the 

 case. Were it so such spots would become among 

 the most valuable on the farm, for potash is of abso- 

 lute necessity in the growth of nearly all plants pro- 

 duced upon the farm. It is an excess of the carbon- 

 ate of soda in the soil which shows as " alkali spots," 

 and which are so great a drawback to farming in 

 many parts of the arid belt. Very little soda is used 

 by plants ordinarily produced upon the farm, hence 

 its presence in excess in any soil is detrimental. It 

 may sometimes be leached away by irrigation arid 

 drainage; and by the free use of gypsum on such 

 lands the effects of the alkali may be neutralized to a 

 very great extent. It is alleged by experienced fruit 

 growers that pears may be successfully grown upon 

 alkali land where other fruits will not grow, 



