DRAINAGE. 



607 



Water percolating from a river should be collected as near 

 it as possible by" deep drains running along the river-side, and 

 leading back into the river lower down stream. Overflow 

 from a stream can be kept back only by the construction of 



C 



embankments, as in the English fen districts, or along the river 

 Severn. 



On slopes, water should be collected at the points of issue 

 from the water-bearing strata, before it can form a swamp. 

 Thus the water should be collected in a drain k k running 

 along a contour-line on the hill-side (Fig. 276), and then 

 conducted down-hill by a leader A along the line of greatest 



Fig. 276. 



k. Feeder, a. Main 

 drain at the base of a 

 hill. 



Fig. 277-. 



D. Chief feeder. A. Main 

 B. Leader from a spring q, 

 small swamp t. C. Feeders. 



drain, 

 and a 



fall, any outlying swampy places in depressions being con- 

 nected with the latter. Wherever the fall and the extent of 

 the area to be drained are considerable, several such drains 

 may be constructed, one above the other. 



