HYDROLOGY OF NEW YORK 



420 



suitable distances apart will be necessary to confine such floods, 

 and enable them to flow off gradually without causing damage. 



From forty-eight years' observation and experience of exten- 

 sive works undertaken for the improvement of rivers, the author 

 can confidently affirm that by careful attention to the points 

 above recommended, even the most tortuous rivers and the 

 swampiest valleys have, generally within a few years, but in 

 some cases only after many years, yielded the most satisfactory 

 results, as for instance — 



a.) The increase of fall due to the more uniform section and 

 more direct course, and the concentration and confinement of the 

 stream within a single channel provided with firm banks, con- 

 siderably increases the force and velocity of the current, which 

 tend to deepen the channel, and to carry away the material thus 

 scoured out as well as that brought down from above. 



b) By lowering the bed of the river, in some cases to the 

 extent of from 3 to 6 feet, the general water level, both of the 

 river and of the ground springs in the neighborhood, is propor- 

 tionately lowered, so that the adjoining country is less liable 

 to inundation, and the swamps are more easily drained and 

 brought under cultivation. 



c) The velocity being accelerated in the new channel, as 

 shown by (a), floods pass off more rapidly and do not rise so 

 high, consequently the low country is seldom or never under 

 water, or at any rate not to the same extent as before. If, how- 

 ever, these lesser and lower floods are to be entirely prevented, 

 dikes parallel to the course of the river must be added. 



d) In rivers exposed to the action of frost, floating ice is 

 apt to accumulate in the unregulated portions of its course, 

 especially at sharp bends, and on shallows and sandbanks, occa- 

 sionally to such an extent as entirely to obstruct the flow of 

 the stream, and to raise the water in the river to such a bight 

 that it overflows the banks, inundates the neighboring country, 

 and spreads ruin far and wide. 



When once a river has been regulated this can not take place, 

 as there would then be nothing to hinder the free passage of 

 floating ice, and should a temporary stoppage occur, the concen- 

 trated force of the current would soon overcome every obstacle, 

 by raising the blocks, and bearing them away without causing 

 any flood. 



e) It is a matter of general experience that even in a deep 

 river following a winding course and dividing into numerous 

 branches navigation is often obstructed to such an extent that 

 the river becomes all but impassable, yet when the same river 

 has been regulated, a direct channel *is provided, facilitating 



