32 BULLETIX 1430, U. S. DEPARTMENT OF AGRICULTURE 
difficult or even impossible to maintain a forest cover over those 
portions of the basins of these streams from which the turbidity is 
derived. In many places it is impossible to maintain a sufficient 
cover of shrubs and grasses to afford even a moderate protection 
against erosion of the soil. 
It is significant that most of the turbidity of the streams of the 
Plains seems to come from below the mountains. As explained in 
the note to Table 1, the headwaters of the Missouri River show a most 
equable flowage as a mountain stream, the maximum flood flow being 
only 24 times the low- water flow. The regimen of the Missouri 
River as it emerges from the mountains is changed by the tribu- 
taries from the Plains. From these tributaries also comes the large 
burden of solid material which is borne by the Missouri in its lower 
reaches and which gives it the unenviable reputation of being one of 
our muddiest rivers, a stream which can well be compared to the 
Yellow River of China. The headwaters of streams which pass 
through the Plains but head within the mountains are materially 
benefited by protection; and all protective cover, whether of grass, 
brush, or forest, should be most carefully maintained. 
At the other extreme from the rivers of the Plains, including 
those of Arizona and those of the southern portion of the Great 
Basin, are those of the Northeast, the Lakes region, including Wis- 
consin and Minnesota, and the extreme Northwest. The streams of 
these regions have a remarkably low turbidity and a low ratio of 
maximum to minimum flow. Reservoirs constructed for storage of 
storm water consequently have a long life. Not that protection is 
not desirable, even in the case of these streams, but of all our rivers, 
the streams of these sections most nearly approach the ideal in the 
eveness of their flow. The distribution of rainfall in these sec- 
tions is such that there is little land which can not be protected by 
means of grass or forest cover. 
The streams of the southern Appalachian and Piedmont region 
and those of California, seem to occupy an intermediate position. 
Normally they have moderate turbidity and have fairly even flow in 
comparison with the streams of the Plains and with those of Texas ; 
but their flow is widely fluctuating when compared with the streams 
of the Northeast. The rainfall is periodically heavy, although 
sufficiently well distributed to maintain an ample forest cover for 
thorough protection. In the Appalachians more than 35 inches of 
rain have fallen within a month and in the mountains of California 
more than 71 inches within the same period. In both regions ex- 
tremely concentrated precipitation frequently takes place, more 
than an inch sometimes falling within much less than an hour. The 
soils are such that, when they are denuded or exposed, erosion pro- 
ceeds at a hight rate; but it is always possible to obtain thorough 
protection by forest or other cover, the forest being as a rule de- 
cidedly most efficient and preferable. 
SUMMARY 
On account of the wide fluctuations in the discharge of streams 
employed for the generation of power, especially hydroelectric de- 
