40 



laterals connected with it, only one outlet being provided for the 

 entire system, which, of course, should be at the lower end of the 

 main. In such a case good drainage might be secured by putting a 

 deep open ditch through the principal hollow, and making the laterals 

 discharge directly into this; but while this system will cost less than 

 the other, because the larger sizes of tiles needed for drains are rela- 

 tively costly, it is not beheved that it will prove equally satisfactory 

 in the end, because the open ditch is liable to numerous accidental 

 injuries (previously referred to) which may lead to the obstruction of 

 some of the laterals. It will be much easier to watch and maintain in 

 perfect condition the one outlet into an open water course on the 

 main than to watch and keep in perfect condition the numerous out- 

 lets required if the laterals discharge directly into an open ditch. 



Direction of Drains. 



The proper direction of drains is determined by the slope. In all 

 cases where the area to be drained is relatively level, it is necessary, in 

 order to secure a satisfactory grade, to run the drains in the direction 

 of the line of greatest slope. In the case of springy slopes, or slopes 

 where water passing through the soil tends to continually crop out at 

 the surface, running the drains obliquely down the slope is generally 

 regarded as the best plan. In this direction they effectively cut off 

 the water which is seeping througii the soil toward the bottom of the 

 slope, while at the same time they have a sufficient grade to carry the 

 water away rapidly. 



Laterals should as a rule run about at right angles with the main 

 with which they are connected. 



Proper Distances between Drains. 



This will vary with the character of the soil. Laterals must be 

 nearer together in proportion as the soil is compact and relatively 

 impervious to water. In a field underdrained by parallel lines of 

 tiles, the usual level of the water table along the lines of tiles will be 

 the level of the bottom of the conduit which they afford, but as the 

 distance in the direction of a right angle from the line of tiles increases, 

 the level of the water table rises above the lavel of the conduit. The 

 water table will be highest between any two lines of tiles along the line 

 midway between them. The rate at which the water table rises is 

 greater in proportion as the soil is compact. In a soil of open character 

 the rate of rise is slight, and lines of tiles which are relatively far apart 

 will hold the water table midway between any two lines at a level 

 sufficiently below the surface of the ground. In a compact soil, on the 

 other hand, the rate of rise of the water table is so rapid that should 

 tiles be placed ecjually far apart tlie water would stand much too near 

 the surface, perhaps at the surface should the lines be placed ecjually 

 far apart. In soils of the most compact character it is necessary. 



