236 



ARBORICULTURE. 



wiien, at very long intervals, extraordi- 

 nary conditions prevailed. 



As in 1832 and 1847, while forest con- 

 ditions existed, both were in midwinter, 

 immense bodies of snow were quickly 

 melted by heavy warm rains, while the 

 ground was solidly frozen and could not 

 absorb the water. 



For all practical purposes we may now 

 compare this water shed to an immense 

 roof covered with slate, and all water 

 must find an outlet in the briefest possi- 

 ble time. 



ERRORS OF UNITED STATES ENGINEERS. 



The War Department, which controls 

 the improvements ( f) of the inland riv- 

 ers, has undertaken to assist navigation 

 by building many expensive dams 

 throughout the length of the Ohio River, 

 with the o'bject in view to concentrate the 

 body of water, at low stage, into a nar- 

 row channel, so that the action of the 

 water may scour out a deeper channel 

 where sand or gravel bars have ob- 

 structed the flow of water and caused it 

 to spread over a broad area, and thus 

 form shallows in the stream. 



To a certain e^ctent this has resulted 

 in considerable gain in depth of channel 

 at these obstructed passages during the 

 verv lowest stage of the river. 



BUT HOW OE ELOOD TIME? 



A river bed will convey away a cer- 

 tain body of water in a certain given 

 time, according to the transverse area of 

 the stream and the fall per mile of the 

 bed or the velocity of the current. 



Decrease the width and depth of the 

 bed without increasing the fall, and the 

 surplus water in flood time must over- 

 flow the banks and spread out over the 

 fertile fields on either side of the stream. 

 The engineers of the War Department 



have attempted to cure the symptoms, 

 l)ut have neglected the disease. 



They have raised the bottom O'f the 

 river bed, and in places obstructed the 

 width of the bed by piers, restricting" the 

 flow of water at flood time, in order to 

 preserve a greater depth of water at 

 low tide. 



A notable instance O'f this obstruction 

 to a river bed is seen at Lawrence, Kan- 

 sas, which we illustrate on page 239. 



Beneath a bridge across the Kansas 

 River the authorities have permitted the 

 construction of a dam six feet in height, 

 of solid masonry, while the bed of the 

 river has been greatly narrowed by piers 

 of masonry at either bank, with a long 

 fill of earthwork upon the north side. 



These obstructions, a few years ago, 

 caused the river to back over the bottom 

 lands above the city, and probably in- 

 fluenced the stream greatly as far as 

 Topeka, w'here the water rose tO' an un- 

 precedented stage, causing vast injury 

 to property, and serious loss and incon- 

 venience tO' the people. 



But the cause, if ever mentioned, was 

 not seriously considered, and still remains 

 a menace to the people and property 

 above the city. 



The steep hills bordering the Ohio 

 River are formed of limestone, while the 

 surface soil is clay. The trees have been 

 removed, all brush and shrubs cleared 

 away along the margins of every rivu- 

 let and stream, so that in time of contin- 

 uous rains the erosion is very great, 

 while so large a proportion is too heavy 

 for water to carry very fast down the 

 stream ; but it is deposited as silt in the 

 bed O'f the river, raising the bottom each 

 year by these deposits, destroying the 

 utility of the Ohio as a navigable river, 

 and in time of flood causing it to over- 



