SOIL EROSION 



373 



laid in the gully to be filled. A vertical tile connects with the 

 horizontal one a few feet above the dam. This form of dam is 

 adapted to comparatively small gullies of slight fall which do not 

 carry large amounts of water. 



The dam holds the soil material carried down by the stream 

 and the water which would otherwise overflow the dam and ruin it 

 passes down through the vertical tile and out through the horizontal 

 one. The arrangement of the tile is shown in figure 1H7. 



Concrete dams are better adapted to large gullies carrying a 



Fio. IRS. Filling n cully 1>\ 



if a cnncrcto d:\ni. 



large volume of water. They should he placed well into the bed 

 of the gully and extended into the Imnk well hack from the gully 

 {Fig. IKS). The concrete should be thoroughly reinforced. A spill- 

 way with an ample concrete floor below the dam is absolutely nec- 

 essary to prevent, the water which passes over from undermining 

 it. The vertical tile is sometimes used as with the earth dam. hut 

 it is not so essential, hut the horizontal tile should he used for 

 draining the temporary pond above the dam. 



