SEEPAGE OR RETURN WATERS FROM IRRIGATION. 7 
In gaging the river at the regular gaging station, which 
is at a point in the Canon above the headgates of all the principal 
canals, a tape is stretched across the river between points on the 
masonry side walls and the depth of the water at each one-foot or 
two-foot interval measured throughout the entire width, which is 
very nearly 100 feet. Then observations were taken with the cur¬ 
rent meter, usually at two-foot intervals, sometimes at less, across 
the stream. As most of these gagings were made at a time of low 
water in the spring, or low water in the fall, the meter has been held 
by hand and the gager has waded the stream. At other points on 
the river where gagings were made the method has been essenti¬ 
ally the same, although the cross-sections have not been as favor¬ 
able as at the gaging station. It is not thought, however, that any 
material error has crept in from these sources. In the notes on the 
measurements some individual sources of error are noted. 
DESCRIPTION OF THE POUDRE VALLEY, IN WHICH THE MEASUREMENTS 
WERE TAKEN. 
§ 8. The measurements have been made on the Cache a la Pou- 
dre river and also on the South Platte. The “ Poudre,” as it is called, 
is the river which drains the valley in which the State Agricultural 
College is located, and is, therefore, the most easy of access for the 
purpose of this and similar investigations. It has the additional ad¬ 
vantage of being one of the largest irrigation streams in the State, and 
one which has been the best used for irrigation purposes, and where 
irrigation has been carried on as completely and successfully as in 
any part of the United States. There is in addition as large a body 
of land irrigated in one tract as anywhere in the United States. The 
phenomena observed are, therefore, found under conditions of irri¬ 
gation on a large scale. They are of great economic importance to 
this valley, and may be expected to hold true of other valleys under 
similar conditions, and where irrigation has been practiced as 
long as it has here. 
The map in the inset [page 16] is intended to give an under¬ 
standing of the conditions which may affect the return waters in 
this valley. The gaging station is indicated near the left of the 
map, below the junction of the north Poudre with the main stream. 
The only canal above this point which needs consideration is the 
North Poudre canal, shown on the map, irrigating some 4,000 acres, 
principally in the valley of the Box Elder. 
The main trend of the valley is to the southeast. Near the 
stream the land is low, the bottom land varying in width from one- 
half to two miles. These bottoms have been occupied in times past 
by the bed of the stream, which is subject to shifting at times of 
high water. With the decrease of floods, and with the use of wate 
for irrigation, the changes are less. 
