482 



EEPORT OF COMMISSIONER OF FISH AND FISHERIES. 



[16] 



structed of earth, wood, or stones, but in all cases the most important 

 point will be the foundation. 



The form of dikes differs according to the locality and the configura- 

 tion of the ground. Bikes may therefore be either straight, or have one 

 or several angles, or be constructed in the form of an arch, «S:c. 



In order to answer their purpose dikes should be so high that they 

 rise from 60 to 90 centimeters above the level of the water. In order to 

 ascertain what height of dike will be required, the exact level of the 

 ground which is to be filled with water should be found. If, e. g., the 

 fall for a certain space a a (see p. 14) has been found to be 120 centime- 

 ters, you add to this the i)roposed heiglit of the dike above the level of 

 the water, say 80 centimeters, and the entire height of the dike should 

 be 200 centimeters or 2 meters. 



E^ 2 



The breadth of the dike at the to]), AC, should be at least 120 

 centimeters, and as a general rule be equal to the depth of the water 

 pressing against it. If, however, the dike is to be used as a carriage- 

 road, its breadth at the top sbould be at least from 3 to 3.5 meters. 



The side of tlie dike which slopes towards the water, also called the 

 front scarp, CELJl), which is principally exposed to the pressure of the 

 water, receives at least the double height, FF, as the base of the slope 

 proper GH, and Iti order to make it still more solid it is covered with 

 stones, fascines, wicker-work, &c. 



The back scar]), AE, at its base equals only the height of the dike, 

 FF, and remains uncovered. 



That part of the dike which is near the outflow of the water sliould be 

 particularly solid, and the bases of both its slopes, both front and back, 

 should be of equal extent. 



The place wliere the water is to liow out should be determined before 

 work on the dike is commenced, the pipes should be laid, and the dike 

 built over them. 



If the sides of the dike are covered with anything — e. r/., stones, 

 &c. — the base-line of the scarp, GH, may be shorter. 



The top of the dike, ABCD, is called the crest, the lines AB and 

 PP — i e., the lines where the scarp commences — the edge of the crest, 



