purington.] HYDRAULIC MINING. 127 
is estimated to be a total of 55 miles of ditches in this basin, including 
the ditch which taps Pargon River, across the divide. The largest 
ditch on this creek carries from 1,200 to 3,000 miner's inches, and is 
through rock and earth for over 18 miles. It was commenced in 
August, 1901, and work has been done on it at intervals up to the 
beginning of the season of 11J04. It is estimated by the Wild Goose 
Mining and Trading Company that on Ophir Creek, in ordinary ground, 
a mile of ditch a week of this size, 16 by 10 by 3 feet, can be built 
with 32 head of horses and 70 men. In the 5 miles of rock work which 
were made along the line black powder was used for blasting. The 
sod walls were found preferable to rock walls in this ditch, as in the 
one built by the Miocene Company. The water is used for working 
several claims, a portion being distributed to each; the head attained 
varies from 170 to 200 feet in the different operations. 
In the construction of the Hot Air Company's ditch line on Ophir 
Creek several long trestles (see PI. XX, B) were found necessary where 
the ditch crossed and recrossed the many meanders of the creek. It 
was necessary to sink the posts of the trestling in rock-tilled cribs or 
piers in the creek bed, as shown in PI. XXI, A. 
The use of inverted siphons is common in many of the Alaska ditch 
lines, but presents nothing new over the California practice. The 
ordinary rules to be observed in conducting water under pressure in 
pipes, the use of large-diameter pipe to prevent excessive friction, 
the calculation of the pressure, resistance, the loss of head, and the 
distribution of air valves are as important as in the case of all pipe 
lines. 
STORAGE RESERVOIRS. 
Lack of water and of sites at a sufficient elevation to afford head 
render the building of extensive storage reservoirs in Alaska impracti- 
cable. The broad, flat valleys, frozen soil, impervious schist bed rock, 
and the excellent sod material for dams offer conditions which appear 
attractive. On the other hand, the small and variable amount of rain 
and snow (see table 2, p. 18) makes it certain that the expensive 
surveys and construction necessary for reservoirs whose capacity runs 
into the millions of cubic feet would never be justified by results. 
Small storage reservoirs have been successfully built and have given 
satisfactory results. The capacity of one built by the Anglo- Klondike 
Mining Company is 400,000 cubic feet, or sufficient to supply 300 
miner's inches for fifteen hours for hydraulicking at a head of 150 feet. 
The dam is 15 feet high and the reservoir is filled from the supply ditch 
in from a few hours to three days, according to the rains, which are 
exceedingly variable. This reservoir, which is built at the elevation 
of the top of the ancient base-level above the highest gravels, is repre- 
sentative of the best that can be accomplished in this line in the interior 
