18 
siderable time is consumed by the water in percolating through the 
soil before it appears again in the springs and water courses lower 
down. 
The forests, especially, aid in holding back the water, for they pro- 
tect both the unmeited snow and the wet ground or surface water from 
the dry winds and sun, and the loose, porous soil of the forests will 
absorb water almost as fast as the snow is melted. In the higher 
un forested areas, the ground being much steeper and with less cover- 
ing to absorb the melted snow, the run-off is much more rapid. 
From the above the following statements are formulated: 
(1) Snows in the early winter in high altitude will furnish a late 
flow, but the amount of late flow therefrom is modified at first by 
the drifting and then by weather conditions as regards rains and 
cloudiness. 
(2) Snows in the forested areas give a better distribution of run-off 
than in unforested areas. 
(3) Years of well-distributed precipitation give a more even and 
later flow in the rivers than years of excessive periodical rains; but 
years of evenly distributed rainfall give a less total of run-off. 
The average run-off for six years was 237 cubic feet per second for 
the entire year. This means a total of 470 acre-feet per da}', or 171,550 
acre-feet per year. 
The drainage area of the Big Thompson above the gauging station is 
given as 305 square miles, or 195.200 acres. The run-off in depth over 
the entire surface is therefore 0.88 foot, or 10.56 inches, as compared 
with 17.18 inches precipitation. This indicates that about 57 per cent 
of the total precipitation would be available for irrigation if it could 
all be stored or should come at such time and in such volume as could 
be used for direct irrigation. This subject will be treated in the dis- 
cussion of duty of water and reservoirs. 
DITCHES. 
In the valley of the Big Thompson prior to 1861 there was very 
little settlement, the gold excitement being much farther south, the 
point farthest north where any mining was done being on Boulder 
Creek. 
It w T as the mines that furnished, in the earliest days as they do now, 
the best and most profitable market; and then, as now, the farms made 
possible the development of most of the mining resources. 
The irrigation of the meadow lands required a great deal of water, 
or. if they did not really require it. it took a great deal to injure them. 
Underlaid, as they usually were, with a bed of coarse gravel, bowlders, 
and wash, they drained quickly, and little alkali was brought to the 
surface, that undesirable substance coming later from the upper lands. 
The higher grounds were leached by the excessive application of water; 
