LAND DRAINAGE PRACTICE. SI 



ural plan for locating lias been hit upon, the whole sys- 

 tem may be developed with ease. 



Secondy more or less work with a levelling instrument 

 may be required in order to obtain the facts necessary 

 for determining upon the best plan of work. The 

 slopes may be so slight, or so deceptive to the eye, and 

 the lines of natural drainage and best points of outlet 

 so obscure, that it will require an instrumental survey 

 to determine them. This involves a certain class of 

 topographical work which will be described hereafter. 



After the Hnes have been located upon the ground, 

 or, more properly speaking, the general plan of work 

 has been decided upon, then their location in the ground 

 as to depth and grade must be done with the level, if 

 any degree of accuracy in the construction of drains is 

 expected to be attained. This part of the work will be 

 described in another chapter. 



