SOIL EROSION 



371 



slope is steeper or the amount of water greater, steps must be taken 

 to [> re vent the rapidly flowing water from washing away the mate- 

 rial used. For this purpose stakes slanting up hill, driven through 

 the straw are used successfully. Hedge or other brush (Fig. 185) 

 placed on the straw help to hold it. Stones may well be used for 

 this purpose, especially if they occur on adjoining slopes. 



Stock frequently make paths up and down steep slopes to such 

 an extent that the grass is killed and a slight depression produced. 

 Water collects in this during rains and a gully is started. 



In pasture lauds, waterfalls sometimes occur that move up the 



slope by means of headwater erosion (Fig. 1S(5). As water goes 

 over the fall it undermines the sod surface, which then caves in. 

 making a gully which is especially dillicult to fill. In such places 

 it is necessary to protect the face of the bank from the undermining 

 action of the water. This may be done by tilling the gully at the 

 fall with brush or straw or both, which must be held in place by 

 stakes or heavy material, such as stones. Since the water from 

 pasture land contains but little sediment, filling of gullies under 

 these conditions is a verv slow process. For completely filling the 

 gullv, dams of sonic kind must be used below the fall. 



2. Dams. In cultivated fields earth and concrete dams are 

 used for filling large irullies. The curlli <!<ini is built over a la rue tile 



