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PULSE OF THE IRRIGATION INDUSTRY 



BROKEN DAM IN IDAHO. 



THE breaking of a reservoir dam, causing a 

 serious flood and suspension of traffic over the 

 railway in Idaho in March, may result in good to 

 irrigation enterprises all over the country. While 

 the reports sent out were greatly exaggerated as to 

 damage done, it was great and serious enough. The 

 breaking of the dam put in by the Orchard Irrigation 

 Company of Idaho for storing water swept away 

 bridges, railroad tracks and embankments. 



While Nampa, Caldwell and the railway company 

 lost much by this flood, to Idaho, and in fact to all the 

 arid regions of the west, it is liable to bring irrepara- 

 ble losses. For years the friends of irrigation have 

 been advocating and urging storage reservoirs as 

 among the most important enterprises in the line of 

 irrigation. Where such have been securely made 

 the results have been all that enthusiastic engineers 

 claimed for them, and capital has been seeking 

 investments in such enterprises. 



The breaking of this dam, however, should result 

 in good in one direction. It will bring about 

 stronger and better construction of dams, and it ought 

 to result in discarding all exclusive earthwork in 

 dams, unless the locality furnishes the right kind of 

 soil or clay to make embankments, which will neither 

 wash, dissolve nor permit seepage. While interested 

 persons claim that this dam was properly constructed 

 the facts as learned from good sources seem to show 

 otherwise. The point selected for the dam was in a 

 canyon nearly fifty feet deep, 100 feet wide at the 

 bottom and 200 feet wide at the top. Here was 

 where the great pressure was to come, while all above 

 this consisting of wings were only low levees, all of 

 the 2,800 feet in dam and wings being sixteen feet 

 wide on top. The slope on the upper side was a 

 rise of one inch in two inches, while the lower side 

 had a slope of one and a half in two inches. This 

 gave a base of 225 feet at the bottom of the dam, 

 which, if made of good clays, would have been ample 

 for much greater pressure than a height of fifty feet 

 of water would ever exert on it. A cut eight feet 

 deep was made across the bottom of the canyon and 

 a stone wall, laid in cement, one foot thick and nine 

 feet high, was placed to prevent seepage. This wall 

 was also extended on the sides where needed. This 

 wall came one foot above the natural surface, and 

 on the upper side of this dirt was placed in layers 



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one foot thick, twenty feet wide and clear across the 

 canyon for puddling. This puddling was accom- 

 plished by wetting these layers by means of pump 

 and hose until well soaked, and then it was packed 

 by means of a two-ton roller drawn by animals. If 

 proper material was used in this construction it 

 seems that it ought to have stood for all time. The 

 outlet of water for use in irrigating land was through 

 a firm tunnel in solid lava, while a waste weir, also in 

 lava, cut six feet deep and 150 feet wide was ample 

 to prevent the water ever rising above a point six 

 feet below the top of the dam and its wings. 



Work began on this dam in November, 1892, and 

 was completed in May, 1893. Doubtless some frozen 

 ground went into the dam. In 1893 the water rose to 

 a point 14 feet below the intended high water mark 

 and the dam did not leak. The water was exhausted 

 during the irrigating season, giving the dam consid- 

 erable time to dry out before the fall rain filled it 

 again up to a much lower point. This was let out in 

 November, permitting the dam to remain dry until it 

 was rapidly filled in March last by rains and melting 

 snow, until it had reached a point four feet higher 

 than ever before, and yet 10 feet below high water 

 mark, when the dam gave way, taking out all the 

 high dam at the bottom 100 feet long, and about 150 

 feet .wide at the top. Nearly all over the Snake 

 River valley the earth is a mixture of quick and 

 granite sands, alkalis, ashes, etc., readily dissolved or 

 made into paste by being wet which, in drying, cracks 

 and leaves open crevices running in various direc- 

 tions. It is most probable that that portion of this 

 dam which was puddled had many crevices formed 

 giving a chance for the water to work its way through. 

 Had this dam been constructed with a light stone 

 wall, so tight as to prevent water leaking through, 

 or even with a lumber filling or bulk head, it is 

 reasonably certain that the structure would have 

 withstood the force of the water, except that the time 

 of the face of the earthwork may have been too steep. 

 Again it is probable that in drying out the shrinkage 

 caused its destruction. This idea is emphasized in 

 the fact that the Mountain Home dam, 20 or 30 miles 

 east and of about the same height, is all right after 

 having been well tested two seasons. Better soil, 

 better construction and more care in puddling made 

 the Mountain Home dam a success and safe 

 structure. 



