Si)| JOURNAL OF FORESTRY 



boring furrows and become rapidly wider and deeper until large gullies 

 of many feet deep are formed. Where hills are thoroughly drained by 

 a system of gullies, the water from a storm will sweep down through 

 them in a fraction of the time that would be required if it had to trickle 

 down in a thin sheet or amidst vegetable obstacles. Now if the main 

 channel is unable to discharge the influx of water as fast as it rushes 

 down, the result is a flood. 



The high rate of run-off, which is characteristic of streams arising 

 from denuded hills and mountains, enables them to carry an enormous 

 amount of silt and bowlders of extraordinary size. The transporting 

 power of water varies as the sixth power of its velocity, so that if the 

 velocity of a stream is increased ten times, for instance, its transporting 

 power is increased 1,000,000 times. This is why, in the case of Chihli 

 rivers, they speak of stones and bowlders of large sizes carried down 

 to the foot of mountains and of the enormous quantity of silt brought 

 down to raise the beds that have already been silted up. 



With this general knowledge of the relation of forests to stream- 

 flow, to soil erosion, and to flood waters, we are in a position now to 

 appreciate better the statements made by the engineers and to under- 

 stand why they all should have emphasized the importance of refor- 

 estation as an indispensable supplement to their hydraulic works. 



The river system in Chihli, with which we are concerned, may be 

 briefly said to consist of the Pei-yun Ho. the Yung-ting Ho, the Ta- 

 ching Ho, the Dze-ya Ho, and the Yu Ho. The first four of these 

 rivers have upland collecting basins in the mountains to the west of 

 Chihli and in Shansi, while the Yvi Ho, or Crand Canal, receives all the 

 water from the Wei Ho, a river rising in the western hills of Honan. 

 These five waterways drain altogether a basin of 75.000 square miles, 

 and of these about 60,000 square miles are mountainous. The five 

 rivers have, as a matter of fact, only one outlet — that is, the Hai Ho. 

 The maximum capacity of the Hai Ho is 30,000 to 35.000 cubic feet 

 of water per second, but, as has been brought out before, the Yung- 

 ting Ho alone carries down as much as 200,000 cubic feet per second 

 during summer freshets. It is evident then that all the water that 

 comes down in excess of the volume disposed of by the Hai Ho must 

 necessarily overflow and become flood water (-n every side. It recuires 

 very little imagination to picture to ourselves the enormous amount of 

 water that the 60,000 square miles of deforested mountains and hills 

 must shed during torrential rains, and then to think further how the 

 water rushes down the hillsides, unhindered by vegetation, nriki-'g 

 gullies and carrying with it enormous amounts of silt. If any of our 



