CHAPTER IV 



DAMS AND HEADWORKS 



1. DAMS 



Classification. Dams may be classified according to the 

 material used in their construction, as: 

 . Timber crib dams. 

 Earth-fill dams. 

 Rock-fill dams. 

 Masonry dams. 



The choice of type is generally dictated by natural conditions. 

 Solid rock foundations usually mean masonry dams, whether of 

 overflow type or not. Absence of rock foundations, however, 

 usually means the choice of crib, earth or rock-fill dams, and which 

 of these is chosen is generally determined by local conditions, 

 such as available construction material, etc. 



Location. Before a final decision can be reached as to the 

 exact location of a dam there are numerous points which must be 

 carefully investigated. For example, with low-head developments, 

 the area which will be flooded must be ascertained as this will 

 determine the available head. It is, therefore, evident that, from 

 this point of view, a dam would be preferable at a point where the 

 river banks are steep so that a sufficient pondage and head could 

 be obtained without causing a flooding of too much adjacent land. 



The character of the soil is also of the utmost importance, and 

 governs, as previously stated, the type of dam which is to be 

 selected. It should be impervious and able to withstand the load 

 of the dam. It is always advisable, especially where a solid rock 

 foundation is not to be had, to dig or drill a number of test holes, 

 from which the character of the underlying strata may be ascer- 

 tained. It may then be found that one site will require a very 

 deep foundation but a smaller dam structure, while at another 

 site the reverse may be true. 



Available material for construction, such as rock, sand, etc., 



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