t THE IMPROVEMENT OF RIVERS. 



Attributed to the mass beneath. By gravity and capillary attraction, acting in 

 opposite directions, it moves somewhat slowly, but finally emerges from the ground in 

 the form of springs, which are more or less constant as the area of the storage is great 

 or small, and dependent also upon the frequency of renewal by additional rainfall. 

 This portion of the rainfall is very valuable to navigation in that it replenishes the flow 

 of rivers at times when there is no water running off the surface, and thus, in regions 

 containing considerable layers of permeable soils, the summer flow is upheld by the 

 natural jtoragn of the winter and spring rains. 



The amount of run-off will also vary considerably with the intensity of the precipi- 

 tation, much more running off in what is called a hard rain, or thunder-shower, than in 

 a gentle fall. It will also be greater when long continued, the earth then becoming 

 saturated so that it can absorb no more. A frozen soil, or a soil hard-baked by the sun's 

 rays, will turn off much more water than the same soil in its natural condition. The 

 rains of summer, while usually heavy within a short period, are largely evaporated and 

 absorbed by the cultivated earth, but those of winter, falling on soil already saturated 

 and possibly frozen hard, readily find their way into the rivers. If these rains are warm 

 and fafl on snow, the conditions are rendered doubly dangerous, as not only the rainfall 

 but also the melting snow will find its way into the already overladen channel. Occa- 

 sionally, however, the opposite effect has been known to result, and a heavy rainfall 

 has been partially absorbed by a deep snow already on the ground and thus held from 

 running off until the flood had begun to subside. A case of this character recently came 

 under our observation, where a rainfall of 10 inches within 48 hours produced less 

 immediate effect upon the river than half the amount would have done under ordinary 

 conditions. The period of high water was prolonged, but its level was kept down much 

 below that which experience had shown would ordinarily follow such a rainfall. 



The melting of snows, when unaccompanied by rains, rarely produces floods in 

 large streams, notwithstanding popular opinion to the contrary. The deepest snows 

 when melted make but a few inches of water, and this reaches the rivers gradually. At 

 night the melting is reduced, or possibly stopped entirely, to be resumed again next day, 

 but even if continuous, with the ground underneath frozen, an unusual condition in 

 many localities, the quantity of run-off will not equal that of ordinary hard rains. 



In many parts of the country the rivers are swollen beyond bounds during the spring 

 and early summer months, only to run almost dry in the autumn, and in studying the 

 characteristics of a stream with a view to its improvement, it is therefore necessary to 

 pOMCM information regarding the rainfall, and the data should extend over as long a 

 period as possible. 



Bed. By the term bed is understood all that space ordinarily covered by water 

 and lying between the lands on each side of a stream. In rivers which rise above the 

 levels of these lands and overflow adjacent bottoms, the channel in which the water is 

 usually confined is called the minor bed, while the space occupied during flood-time is 

 known as the major bed. The difference in width between the two is frequently very 



