18 THE UTILITY OF FORESTS. 



has been expressed that on level ground less water reaches the 

 underground water reservoirs in forests than in open ground. 

 In so far, forests would act unfavourably as regards the feeding 

 of springs. On hilly ground, however, a smaller proportion of 

 the rainfall rushes straight away into the water channels in forests, 

 giving the rest time to infiltrate into the soil. Observations 

 made in the Russian Steppes and in Northern Russia indicate 

 that the water level was lower in forests than outside. Similar 

 results were obtained in France. On the other hand, observations 

 made in Bavaria, Alsace and Switzerland have shown that no 

 general rule can be laid down on the subject. As a matter of fact, 

 the underground water level depends chiefly on the nature of the 

 geological formation, that is to say, on its permeability. The 

 configuration of the ground also causes great differences. 



The above considerations govern also the water level in rivers, 

 in so far as forests retain a large portion of the falling rain, if not 

 permanently, at any rate for some time, thus enabling rivers to 

 spread the discharge of their water over a longer period of time, 

 resulting in a reduction of the flood level. 



When the forest humus has been saturated with water, and rain 

 continues, its effect as regards inundations must cease, because 

 the additional water follows the law of gravitation and finds its 

 way into the valleys. Hence, these effects are of Hmited extent, 

 a matter which has been frequently overlooked. To moderate 

 inundations to any appreciable extent, it is necessary to keep a 

 very large proportion of the catchment area imder forest. On the 

 other hand, well-stocked catchment areas produce a steady flow 

 of water during the dryer part of the year, and thus keep up a 

 higher level in rivers at these seasons for the supply of water for 

 irrigation and other purposes. 



(b) Protection of the Soil. — Water rushing down a bare hillside 

 possesses a great mechanical power, by means of which it loosens 

 the soil and carries it downhill. In this way landslips are 

 frequently caused, ravines formed, and fertile lands at the foot 

 of the ravines covered with silt and rendered useless. Frequently 

 the debris collects in the rivers and forms obstructions, which are 

 followed by a diversion of the bed and erosion of fertile lands. 

 The rate at which this damage proceeds depends on the geological 

 formation and the formation of the surface ; the less binding the 



