12 BULLETIN 1026, U. S. DEPARTMENT OF AGRICULTURE. 
intercepted for direct use or for storage. A conservative estimate 
of the amount of this seepage would be 12,000 acre-feet. Added to- 
gether, these give a total seepage return for the valley of approxi- 
mately 137,000 acre-feet annually, which is equivalent to a constant 
flow of 190 second-feet. The average annual water supply of the 
valley, exclusive of seepage, is 380,000 acre-feet, and the seepage re- 
turn as estimated above is slightly over 36 per cent of that supply. 5 
DRAINAGE CONDITIONS. 
From the preceding section on seepage return the natural pre- 
sumption would be that drainage must be one of the important prob- 
lems of the valley, but such is not the case. As is to be expected in 
any irrigated area, for many years wet spots have developed, but 
these spots rarely exceeded 40 to 80 acres in extent and were usu- 
ally drained as soon as the condition became bad. Because of the 
rolling topography, the sandy character of the soil, and the many 
natural channels, the construction of the required small systems of 
tile drains presented no difficulties. It is estimated that close to 10 
per cent of the irrigated land of the valley is underlain by drains. 
Land needing drainage at present is in scattered spots and in only 
two instances is there as much as 500 acres in one body. 
EXCHANGE OF WATER. 
In order to utilize sites which could be developed cheaply and 
at the same time to save the cost of intake canals, 12 reservoirs of 
the Cache la Poudre Valley, with an aggregate capacity of about 
50,000 acre-feet, were built below the distributing canals of the com- 
panies owning them. The problem of making the water stored in 
these reservoirs available for use in the distributing canals above 
has been solved by the development of a very complicated system of 
exchange of water. In 1916, an average year, the operation of the 
exchange system made available for use on higher land about 55,000 
acre- feet of water stored in low reservoirs, or 14 per cent of the total 
supply used by all the canals of the valley. 
The principal exchange system of the valley involves the 4 largest 
canals, and to understand it clearly a few facts must be kept in mind. 
Beginning at the lower end of the river and going upstream, the 
Greeley Canal No. 2, the Larimer and Weld Canal, and the Larimer 
County Canal of the Water Supply & Storage Co. head in the order 
named. Next above and diverting from the North Fork is the North 
Poudre Canal. The principal water rights of these canals stand in 
the same order of priority, the Greeley Canal No. 2 coming first 
with an appropriation dating 1870 and the North Poudre Canal com- 
ing last with an appropriation dating 1881. Keservoirs No. 5 and 
No. 6 of the North Poudre Co. are too low to supply directly any 
land under the canal, and their outlet empties into the Larimer County 
5 This does not include seepage from Poudre Valley land entering directly into the 
South Platte. 
