\\^\TER CIRCULATION AND ITS CONTROL 



331 



The topographic character of the re- 

 gion is favorable to the construction of 

 large numbers of small reservoirs to 

 catch the flood run-off from near-by 

 fields, and this item in farm equipment 

 should become as much a matter of 

 public interest and control as the main- 

 tenance of public roads. But the silt 

 from badly tilled fields will render res- 

 ervoirs useless unless the farmer pre- 

 vents erosion. The larger factor in 

 control must be found in improved 

 methods of tillage and crop rotation. 



A fourth district which presents spe- 

 cial conditions in regard to storage is 

 that of the ^Appalachian Mountain re- 

 gion. Here topographic forms are such 

 as to render reservoir construction both 

 difiicult and expensive. ' The narrow 

 valleys alone offer possible sites. Their 

 steep gradients necessitate high dams 

 for reservoirs of moderate capacity. 

 Where wide bottom lands afford better 

 opportunities important towns are com- 

 monly located. Moreover the efficiency 

 of such reservoirs must be low, because 

 the flood run-oft' is torrential and some 

 considerable part of it nuist be per- 

 mitted to escape. We may not, how- 

 ever, conclude that reservoirs are im- 

 practicable. 



The Appalachian Mountains have 

 always had and will always have spe- 

 cial relations to national development. 

 Their mountain Avail guarded the col- 

 onies during a century of French and 

 Indian warfare. Eventually occupied 

 by American enterprise, the region be- 

 came through its resources in minerals, 

 lumber, and water power a dominant 

 source of national strength and wealth. 

 It can never support a large agricul- 

 tural population, yet the mountain 

 dwellers will cultivate their fields in its 

 upland valleys so long as the soil re- 

 mains. Its mineral wealth will cer- 

 tainly be exhausted, but its fc^rests and 

 streams, those two intimately related 

 and most valuable factors in the Na- 

 tion's prosperity, need never be im- 

 paired though continually used. 



These mountains possess a power to 

 do harm which is not less than their 

 power to confer benefit. The floods 

 that ijather from their rills traverse the 



richest cities, manufacturing districts, 

 and valleys, and exact annually an 

 enormous tribute. The cost in dead 

 loss, in lessened values, and crippled in- 

 dustries will eventually force the Na- 

 tion to protect itself. There are men — 

 engineers, too — who believe they can 

 fetter the full-grown flood, but the com- 

 monwealth which trusts to them alone 

 and neglects the agencies of forestry 

 and agriculture that divert the rain- 

 drops will suffer till it has bought wis- 

 dom dearly. 



Thus throughout this mountain re- 

 gion the problem of controlling surface 

 waters is not only particularly difficult, 

 but its solution is peculiarly important. 

 The engineer has here a grave and dif- 

 ficult task to perform, and even under 

 the unfavorable local conditions the 

 storage reservoir must take its place as 

 one of the features of the system of reg- 

 ulation. 



In our general discussion drainage is 

 next. It stands in direct contrast to 

 storage. It promotes quick discharge, 

 increases flood run-off, and dries up 

 swamps that storage would convert into 

 reservoirs. No region from which in- 

 jurious floods gather should be drained, 

 for the drainage system will increase 

 the floods. On the upper Mississippi, 

 for instance, we would not drain the 

 reservoirs produced by artificial dams, 

 nor should we drain swamps that empty 

 into them or into the river below them 

 without dul}' consi'lering to what ex- 

 tent our left hand is undoing the work 

 that our right hand has done. 



Yet drainage has its place in the na- 

 tional management of surface waters. 

 It is appropriate in lands liable to over- 

 flow and which may safely be permitted 

 to return the waters promptly to the 

 stream as the river falls. It is ]K"rmis- 

 sible in lands whose value when drained 

 exceeds the value of lands that the 

 drainage waters may submerge. Here, 

 as indeed generally, throughout this 

 whole question of conservation the re- 

 sulting value determines whether or no 

 the thing should be done. 



Diversion canals are designed to take 

 a part or all the water of any system 

 and conduct it from the channel in 



