104 OUR USE OF THE LAND 



diverted a large part of precipitation from the absorption route 

 to the run-off route. 



The absorbing power of land is also related to the amount of 

 slope. This is the second factor which controls run-off. Water 

 will pour down a steep hillside more quickly than it will down a 

 gradual hill. Practically all the water that falls in rain will 

 run off a bare slope of 3 per cent. From this you can see that 

 the volume of water lost by run-off may be very great even on 

 slight slopes. The steeper the slope, the greater the speed of 

 the running water. The faster the run-off, the more soil it will 

 carry. Consequently, in the use of sloping land, much greater 

 care is needed than on level land to get water into the soil and 

 to prevent it from running too fast. 



There is a third factor which affects run-off. That is the 

 quality of the soil. Sandy soil absorbs water quickly. This means 

 that there is little run-off. Clayey soil, on the other hand, is 

 close-grained. When it is wet it has a smooth, slippery surface 

 which sheds the water. Consequently the run-off on clayey 

 soils is greater than it is on sandy soils. This is but a simple 

 example of a very complicated process. There are many types 

 of soils and many reasons why they do or do not absorb water. 

 The important thing here is that the quality of the soil helps 

 to determine the amount of run-off. 



A large amount of run-off is a bad thing. There are two 

 principal reasons for this. In the first place a high rate of run 

 off means a high rate of erosion. When we speak of erosion 

 here we mean the washing away of the soil. 



In the second place, when water runs off the surface of the 

 land, the ground water reservoir is cheated out of just that 

 much supply. This ground water reservoir is very important. 

 It is the source of a large amount of stream flow and well 

 water. Ground water nourishes trees and other plants during 

 dry seasons. In the summer, when the other sources of water 

 have shrunk, the ground water reservoir continues to send 



