FORESTS, RESERVOIRS, AND STREAM FLOW 287 
Reservoirs in Turir RELATION To StREaM FLow. 
Under this heading artificial reservoirs alone are included. 
Natural reservoirs of various kinds exist nearly everywhere, and exert 
a profound influence upon stream flow. The ground is the most 
important of these, absorbing on the average probably one-third of 
the total rainfall. Natural lakes are great regulators, the St. Lawrence 
system being the most perfect example. Forests are effective reservoirs 
at certain seasons. Swamps and low-lying grounds along river courses, 
like the great flood basins of the Sacramento and the Mississippi, are, 
in their natural state, enormous reservoirs which greatly reduce the 
flood flow of the river channels. Snow-drifts, particularly the great 
drifts of the mountains, are splendid reservoirs. The streams them- 
selves have immense storage capacity; for example, the Mississippi 
within levees stores at least 2000 billion cu. ft. of water from Cairo 
to the Gulf, between extreme high- and low-water stages. All these 
reservoirs and many of less importance are ever active in regulating 
the flow of streams. Without them, precipitation would flow off as 
fast as it arrives, and our greatest floods would be magnified many 
times. 
Here we are considering only those reservoirs constructed by Man 
to supplement and extend the regulating effect of Nature’s reservoirs. 
If the conclusions reached in the first section of this paper are cor- 
rect, forests cannot be relied upon in any degree to help solve the 
problems of high and low water. Present conditions must be met 
by purely artificial means, since Man has so far discovered no way 
of controlling the climatic conditions which govern precipitation. He 
cannot “stay the bottles of heaven” in times of flood, nor open them 
in seasons of drought. He must take the water after it reaches the 
earth, and deal with it the best he can. 
The artificial reservoir is intended to attack this problem at its 
source. It catches and holds back the water in the near vicinity of 
its deposition, instead of waiting until it gathers into the rivers, and 
then building huge bulwarks to contain it there in times of flood. 
It saves the stored-up supply and gives it out in the low-water season, 
thereby helping navigation, instead of dredging and otherwise treat- 
ing the watercourses to increase the low-water depth. It corrects 
one of the greatest deficiencies of Nature by abolishing inequalities of 
stream flow and converting waste into utility. Theoretically, it is 
