Land Drainage in New York 1665 



two to three feet. In sandy hind the drains maj he placed deeper 

 than in clay land. Up to a depth of four feet an increase in the 

 depth of the drain will permit an increase in the interval between 

 drains of about two rods for each foot in depth. In clay land an 

 increase in the depth of layins; the tile will usually not permit an 

 increase in the interval between drains. 



GRADE 



Drains must always have some grade to insure the flow of water. 

 If the direction or extent of the natural grade is questionable a lev- 

 eling instrument should be used to determine the conditions. 

 Often a home-made instrument using a carpenter's level is very ser- 

 viceable. 



A very small grade will suffice for the flow of water in a tile. 

 Tile drains will operate on a grade of a half inch per hundred feet 

 but a fall of six inches to a foot per hundred feet is much more 

 desirable. The less the fall the more careful must be all the con- 

 struction to insure permanency, and relatively larger tile must be 

 used. In soils of a quicksand nature it is important that the lat- 

 eral drains should have no greater grade than the main or that silt 

 wells be constructed at intervals to collect the sediment and permit 

 its removal. 



SILT WELLS 



A silt well is a pit in the course of the drain, the bottom of which 

 extends two or three feet below the line of tile. The water comes 

 in at one side and goes out at the other. Any coarse material will 

 settle to the bottom. One or two sections of sewer tile placed on 

 end with junction connections make the most simple and perma- 

 nent construction. Surface water may to advantage be admitted 

 through the silt wells, thereby protecting the system of drains from 

 surface wash. 



SIZE OF TILE 



The size of tile, will, of course, vary with the area drained, the 

 grade and presence of surface and underground courses. The tend- 

 ency of the day is to increase rather than decrease the minimum 

 size of tile used. In general, tile smaller than three inches should 

 not be used. From that size they will increase according to the 

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