DISCUSSION : FORESTS, RESERVOIRS, AND STREAM FLOW 481 
observation and experience touching the important and vital features Mr. McMath. 
of one of the chief living questions of the day.” 
The writer feels disposed to protest mildly against the limiting 
clause of the title, “Reference to navigable rivers,” because he knows 
no definition for navigable rivers, nor where to draw the line between 
the flotation of a chip and the largest ship. In the conservation and 
utilization of stream flow, as one of Nature’s beneficencies, navigation 
comes last, but is not chief. 
In discussing the paper, the writer would amend the title to read, 
“Reservoirs and forests in their relation to stream flow.” Nature has 
determined the question of precedence by the fact that reservoirs are 
one of the controlling elements of stream flow, and has located reser- 
voirs at every step from the hilltop to the ocean, and supplies water 
to fill the entire system from the great reservoir, whose importance 
in the administrative economy justifies the fact that three-quarters 
of the earth’s surface is ocean. Incidentally, the oceans are useful 
for navigation, and the same is true, to greater or less degree, of 
the rivers emptying into them. The chief end of rivers is not naviga- 
tion, but the conveyance of waters from higher to lower levels. 
Nature has provided, a goodly number of possible sites for artificial 
reservoirs to supplement the natural sites. The engineer who belittles 
reservoirs, their uses and possibilities, has not grasped the fundamental 
principle of river engineering. 
In the final analysis it will be found that the possibility of reservoir 
extension is the measure of the success that may be hoped for in the 
way of a permanently improved Lower Mississippi, and a permanently 
protected delta, from the Ohio to the Gulf. This is a large assertion, 
but the proof is at hand. 
Water at a high level represents potential energy, mass into head, 
Q X H. In the passage of water from mountain top to ocean this 
potential energy must be expended in work. 
If we assume the average volume of the Mississippi below the 
Ohio to be 500000 cu. ft. per sec., and the elevation at that point 
to be 250 ft., there is a potency of about 20000 000 h. p. to be expended 
in work each minute along some 800 miles of river. 
If men load the stream with 100000 tons of freight and let it 
float with the current, the load increases the mass, but the head is 
still H. The potency is (Q+ q) Z. 
If Nature loads the stream with mud, silt, sand, and gravel to an 
aggregate of q,, the capacity for work is represented by F (Q + 4,) sy ; 
1 being distance. 
As a matter of fact, Nature does not give a through bill of lading 
for the freight it commits to the river, but the load is dropped at way 
stations, as bars and accretions, and is replaced, in a measure, by scour 
