FIXED DAMS. 



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latter covering is omitted the ripples and waves from the dam, which form the agency 

 by which the banks are cut, play through the openings in the stones and wash upon 

 the soil with a force very little diminished, and soon carry away the particles of earth. 

 We have seen the two methods tried side by side upon a bank just below a dam, and 

 the portion protected by riprap alone was eaten away almost as though no stone lay 

 upon it, while the portion on which spalls had been placed was unaffected. 



The protection of the banks is a matter which is usually neglected until some 

 action is absolutely necessary. This is unfortunate, as by that time the bank has 

 usually become badly washed and must always remain an eyesore. Had the remedy 

 been applied at the proper time, the ultimate expense would have been no greater and 

 the disfigurement of the property would have been avoided. 



Several notable examples of the results of lack of bank protection are to be seen 

 in this country. On one river the water at some of the locks has eaten into the bank 

 till it has excavated an area of several acres, below and behind the land wall, which in one 

 case resulted in the river washing its way during a flood around the upper wing wall 

 into the basin and causing very serious damage. 



Masonry Dams. Several examples of masonry dams of concrete or of stone are 

 to be found in rivers in this country, while still others are proposed. Where the 

 foundation is good they are preferable to timber dams because of their durability, 

 although they are of course more expensive. The principles governing their design 

 and construction are the same as those for storage reservoirs, except that the effects 

 of the overflow must be provided for. They should always be composed of concrete 

 or of large stone laid in good cement mortar, so as to secure a structure which will be 

 water-tight and stand the attacks of drift and floods. A dam of this class built with un- 

 suitable materials is a source of constant trouble and expense, and may eventually 

 have to be removed and rebuilt. 



COST OF FIXED DAMS. 



