48 ENGINEERING FOR LAND DRAINAGE. 



drain through some short cut than by the natural over- 

 flow course. This is a matter, however, that should 

 be examined with care before a location is made. 



Laterals should be laid in the line of greatest 

 slope. Many think that by extending a drain across 

 a slope, water coming through the soil from above will 

 be intercepted by the drain and thus be prevented from 

 passing further toward the foot of the slope. Practice 

 has proved this to be a mistake. Lines for conveying 

 the drainage-water may be located at right angles to 

 the slopes if placed so far down on the bottom land 



30 feet 

 Fig, 9. — Water-line in Retentive Clay Soils. 



that the grade of the drain is greater than the slope of 

 the surface at the side, as a few facts will show. Water 

 oozes through the soil along the line of steepest de- 

 scent, at all times seeking a lower place where it can 

 remain at rest. If a drain is placed across this course 

 of soil water, the descent of the soil channels being 

 greater than that of the drain, water will flow out of 

 the joints of the drain and continue to ooze through the 

 soil, only a small part being conveyed away by the 

 drain. Place the drains up and down the slope, and 

 all water coming into the drain will be carried away 

 quickly, and little currents induced to flow toward the 

 drain from both sides. See Fig. 9. 



