BEAVEE DAMS. 375 



themselves with the smaller amount of labour involved i;: 

 eth building of a stick dam. 



To give some idea of the proportions of a dam, I shall 

 epitomise a number of measurements given by Mr. 



Morgan : 



Feet 



Height of structure from base line . . . . 2 to 6 



Difference in depth of water above and below dam . 4 to 5 



Width of base or section . . . . . . 6 to 18 



Length of slope, lower face . . . . . 6 to 1 3 



Length of slope, upper face . . . . 4 to 8 



The only other measurement is that of length, and this, 

 of course, varies with the width of water to be spanned. 

 Where this width is considerable the length of a dam 

 may be prodigious, as the following quotation will show : 



Some of the dams in this region are not less remarkable 

 for their prodigious length, a statement of which, in fact, would 

 scarcely be credited unless verified by actual measurement. 

 The largest one yet mentioned measures 260 feet, but there are 

 dams 400 and even 500 feet long. 



There is a dam in two sections, situated upon a tributary of 

 the main branch of the Esconauba River, about a mile and 

 a half north-west of the Washington Main. One section 

 measures 110 and the other 400 feet, with an interval of 

 natural bank, worked here and there, of 1,000 feet. A solid- 

 bank dam, 20 feet in length, was first constructed across the 

 channel of the stream, from bank to bank, with the usual 

 opening for the surplus water, five feet wide. As the water 

 rose and overflowed the bank on the left side, the dam was 

 extended for 90 feet, until it reached ground high enough to 

 confine the pond. This natural bank extended up the stream, 

 and nearly parallel with it, for 1,000 feet, where the ground 

 again subsided, and allowed the water in the upper part of the 

 pond to flow out and around into the channel of the stream below 

 the dam. To meet this emergency a second dam, 420 feet long, 

 was constructed. For the greater part of its length it is low, but 

 in some places it is two and a half and three feet high, and 

 constructed of stick-work on the land, and with an earth 

 embankment on its outer face. In effect, therefore, it is one 

 structure 1,530 feet in length, of which 530 feet in two sections 

 is artificial, and the remainder natural bank, but worked here 

 and there where depressions in the ground required raising 

 oy artificial means. 



