The Washing of Soils 337 



PRINCIPLES GOVERNING THE WASHING OF SOILS 



One of the commonest mistakes of beginners in 

 irrigation is the use of too large volumes of water 

 in a place and hurrying it over the ground too 

 rapidly. It must be kept ever in mind, in all sorts 

 of irrigation, that the eroding and transporting power 

 of water increases with the velocity with which it 

 moves, but in a higher ratio ; to double the rate at 

 which water moves in a furrow or over the surface, 

 increases its power to wash and carry the soil for- 

 ward nearly fourfold. 



In good irrigation, the water is forced to move 

 so gently that it runs nearly or quite clear and with- 

 out washing the sides or bottom of the furrows, and 

 if one does not succeed in securing flows without 

 washing, the only conclusion which should be drawn 

 is that the right way has not yet been learned, not 

 that it cannot be done. 



Naturally, the steeper the slope of the furrows 

 the faster the water tends to run. So, too, when the 

 slope remains the same, the larger the volume of water 

 in the furrow the faster the water will flow, and these 

 two principles give the irrigator nearly complete con- 

 trol of the situation. 



If the ground is flat and the water moves too 

 slowly, increase the amount in the furrow, and if 

 there is not water enough to do this, decrease the 

 number of furrows handled at one time. If the water 

 runs too fast and washes, divide up the stream, lead- 

 ing it into more furrows until the movement comes 



