218 IRlilGATION. 



As a general rule, for dams of not more than 

 20 feet in bight, when earth of the best kind, or such as 

 is mentioned above, can be procured, puddling may be 

 dispensed with. When puddling is used, it would seem 

 to be more properly placed upon the inner side of the 

 work, with the selected material next to it, and the poor- 

 est used as a backing to support the work ; this, although 

 seeming reasonable, is not in accordance with practice, 

 and no one seems inclined to risk the innovation upon an 

 accepted custom, with the risk of blame for it in case of 

 failure from whatever cause. 



The first requisite, in constructing a dam of any magni- 

 tude, is to ascertain the character of the foundation, and 

 to excavate this to a bed of solid rock or impermeable 

 earth. If springs are encountered the location may be 

 abandoned and another chosen, or else the spring must 

 be carried away in tight drains, beyond the outer slope 

 of the dam. The channel for the water flow is then to 

 be constructed in case the dam is to be used for a reser- 

 voir in the solid subsoil, and the pipes or culverts used 

 for this purpose should be flanged every few feet of the 

 length, that the puddling around them may be more 

 thoroughly compacted, and the danger of leakage at this 

 most important point, by the creeping of the water along 

 the surface, be prevented. All disturbance to the pipes 

 or culverts, by settling of the work, which might occur 

 if they were placed in the body of the dam, is thus 

 avoided. 



The best of the selected material is then disposed in 

 thin layers upon the foundation, and well rammed, or 

 puddled. The puddle wall may be carried up in the 

 centre of the selected earth or clay, or upon the inner face 

 of it; which, although an innovation upon established 

 practice, would be an improvement upon it. The earth 

 should be brought to the dam by carts, in preference to 

 wheel-barrows or to tip-cars upon a track although the 



