6 
BULLETIN 82. 
164.4 second feet; and in 1901, 167 second feet. This gain, or the 
amount of water returning to the river, varies for different sections 
of the river, and also from year to year. The minimum flow of re¬ 
turn waters which I find given was in March, 1894, when it amount¬ 
ed to 82.3 second feet. (Bulletin No. 33 of this Station.) The per¬ 
centage of seepage water in the river at any given point will evi¬ 
dently vary from time to time, but taking the whole course of the 
Poudre from below Bellvue down to its mouth the amount varies 
from a small amount to 100 per cent. In order to obtain river 
water free from seepage, it is necessary to take it above the head- 
gate of the ditch furthest up the stream; in fact we found it ad¬ 
visable to take it above the mouth of the North Fork. 
§ 12. The river water as it is delivered to the town of Fort 
Collins, for domestic consumption, is, from a chemical standpoint, 
a good water for domestic purposes; but a comparison of it with the 
river water taken further up the stream shows that it has already 
suffered a considerable change, due to admixture of seepage which 
has found its way to the river. The object had in view in taking 
the samples of this water was not to examine it to determine its fit¬ 
ness as a potable water, but simply as a part of the larger questions 
relative to the changes suffered by the water when used for the 
purposes of irrigation. 
THE CACHE A LA POUDRE RIVER WATER. 
§ 13. The Cache a la Poudre, very generally called the 
“Poudre,” and its tributaries, drain a mountainous area of about 
1,050 square miles before it enters the plains section. These 1,050 
square miles of drainage area present a varied surface, some of which 
is wooded or covered with other vegetation, much of it being naked 
rocks; but whether covered with a thin mountain soil, a rich valley 
soil or rotten rocks, there is everywhere one constant condition. 
The rocks are largely granite, and the soil, very naturally, is gran¬ 
itic too. The waters flow over granite bowlders, are retained in the 
interstices of granitic sands or soils, and whatever mineral matter 
is taken into solution by the waters is derived from the minerals 
making up the granite, gneiss or schist, as the case may be. The 
snows on the mountains by their melting yield the water which 
finds its way to the valleys to be later used for immediate irrigation 
or stored for subsequent use. I shall endeavor to follow the 
changes produced in the composition of this water from the time it 
melts, when I shall assume it to be practically pure water, until it 
leaves the Poudre to join the Platte. There are many difficulties 
in this study, and I shall be compelled to leave many questions 
wholly unanswered and others with very general answers. 
§ 14. The most surprising change in the series suffered by 
this water is perhaps the very first one, that is, the change produc- 
