Drainage in New York. 



269 



they may rise to the surface. If the volume of water to be 

 handled is very large, the length of the filter may be increased 

 or what is less desirable, the tile may be separated a small 

 fraction of an inch to permit the more ready entrance of the 

 water. Types of stone sinks are shown in Figs. 212 and 213 and in the 

 latter is shown a modified form in which a wooden box with parts 

 of the sides closed by wire screen. This screen box is sometimes 

 combined with the silt basin. The silt basin is a well in which the 



coarse soil particles may settle 

 while the water is drawn ofif at 

 a higher level where it holds 

 only the material which may 

 be carried. In this case the 

 silt well is constructed in the 

 course of the ditch and one 

 or more lengths of tile are 



removed. 



This 



Fig. 212.— BiiHcd stone filter and sink fo'^^^^^'^^^- -i ^is same con- 



facilitate entrance of surface water into tile, struction of the silt well is 



used where it is necessary to 

 join several laterals at one point with a main ditch which has a dif- 

 ferent grade. The bottom of the well may extend several feet below 

 the level of the tiles and any heavy material will fall to the bottom 

 where it may be easily removed instead of being collected in the tile 

 where it may cause damage. 



The clogging of tile by sediment is 

 serious only in drains having a 

 relatively small fall — say less than six 

 inches per 100 feet. Where the fall is 

 greater than this amount, there is a 

 very decided scouring action of the 

 water which will handle any material 



which may enter a fairly well-made Fig. 215. — Stone sink and Alter with 

 • • ^ screened box intake. 



(e) Size of tile- 



The proper size of the tile is one of those details for which no explicit 

 directions can be given. Since the cost of tile increases very rapidly 

 with increased size, as small tile as will meet the conditions should be 

 used. But no risk should be taken of using too small tile. The increased 

 cost of the larger sized tile is small compared with the total cost of 

 constructing tile drains and too small tiles at the outlet may render a 

 whole system relatively ineffective. 



On the other hand, it is undesirable to use too small tile. Where 

 the fall is less than one-half foot per 100 feet, no tiles smaller than 3 inch 

 should be used. With small tile a relatively small discrepancy in grade 

 may throw the whole line of tile out of commission while with a larger 



