36 DRAINING OF GROUND, ETC. 



length of the small drains themselves — for if these 

 are of great length, and put in pretty close upon 

 the ground, they will, during a flood, pour a great 

 quantity of water into the main drain : but to avoid 

 the consequences of too much water falhng into any 

 main drain, it is a better plan not to allow any 

 small drain to run above one hundred yards without 

 falling into a main, or at least a sub-main one, which 

 again empties itself into a main drain. 



In putting open drains upon land having a na- 

 tural declivity, they should be run nearly at right 

 angles with the descent of the ground ; but at the 

 same time, care must be taken to make every drain 

 with a slight fall downwards ; for if they have not 

 at least one foot in a hundred of descent, they will 

 be apt to become choked up with mud and other 

 vegetable matter, which is sure to accumulate, if 

 not carried away by a brisk run of the water in the 

 drains. All drains made upon what is generally 

 termed a dead-level, soon become useless; there- 

 fore, the great point to attend to for the keeping of 

 drains in a clear state is, to give them a good brisk 

 run for the water, as it issues from the sides. How- 

 ever, caution is necessary lest this should be over- 

 done ; for if the ground be sandy or gravelly, a 

 rapid descent would prove dangerous by under- 

 mining the sides of the drains : consequently, it 

 should always be observed, that where the soil is 

 light and sandy, just so much descent should be given 



