COLORADO IRRIGATION WATERS AND THEIR CHANGES. 5 
ing the water available for irrigating other land. From this time 
on water will be made to do duty repeatedly in the production of 
crops, even more so than at present, especially if the fall of the 
river and other conditions will permit it. 
§ 9. For these reasons the Pondre presents the best subject, 
and the present is probably the most opportune time that has yet 
presented itself for such a study. The chemical questions relative 
to the composition of the return waters will become more involved 
within the next few years than they are now, because an increasing 
percentage of such water will have been used repeatedly before it 
makes its appearance as such in the river. Some of it will have 
passed into storage reservoirs and suffered whatever changes that 
may take place during the time of storage. One of the largest res¬ 
ervoirs within this valley has recently been completed, the purpose 
of which is to collect and render available waste and seepage or re¬ 
turn water. 
§ ro. The course of the river after it issues from the canyon 
is over the jura-triassic and cretaceous formations. The character 
of the river bed has but a slight influence upon the composition of 
the water compared with that of the return waters, the percentage 
of which increases as one goes down the stream; not simply because 
there is an increase in the number or size of the inflowing streams 
and springs, but also because of the amount of water which has 
been taken out in the upper parts of the river. There are six larger 
and several smaller ditches taking water from the Pondre between 
the mouth of the canyon and the town of Fort Collins. These 
ditches take at least four-fifths of the water flowing in the river 
above the first ditch. The gagings show that there is a small loss 
of water between the gaging station in the canyon, and a point be¬ 
low Bellvue, the city water works; but from this point on to the 
mouth of the river there is an irregular but increasing gain. The 
sewage from the town of Fort Collins, and also that of the College, 
which is an independent system, flows into the river below the 
town. The college system also carries a considerable volume of 
drainage water. The total volume of water returned to the river 
in this way is large, representing the sewage from a population of 
5,000; but the total mineral matter added to the river water by the 
drainage is probably greater than that contained in the sewage, and 
this represents but a very small fraction of the mineral substances 
brought in by the return waters. 
§ 11. There is much irrigated land in this district, from 
which the seepage and waste waters together with waste from the 
ditches, begin to return, as shown by the measurements of the river 
several miles above Fort Collins. There is a gain beginning a lit¬ 
tle way below the town of Bellvue, which increases as we go down 
the river, until at its mouth the total increase reached, in 1895, 
