48

Thompson at a point 40 miles above Kamloops are available from 1915 to
1922. They show an average run-off of nearly 25 inches over the drainage
basin, the higher parts of which are fairly similar to Barkerville area. The
annual pregipitation over the drainage basin is known to be slightly greater
than at Barkerville and probably averaged between 45 and 50 inches during
the period, or about double the amount of run-off. It is probable, therefore,
that the run-off in the Barkerville area is about one-half the precipitation.

Weir measurements of many of the streams were made by the present
writer in August and September, 1923, during which year the precipitation
was practically the same as the average for thirty-six years. The average
run-offs (depth of water over the drainage basins) of the creeks during
August and September were determined from these measurements and
from the areas of the drainage basins. In most cases it was found that the
run-offs for these months were only one-fifth of the precipitation. The
run-offs for the other months of the year were then determined by assuming
that the run-offs are proportional to those which obtain in the drainage
basin of the North Thompson, for which monthly records are available.
The results indicate that the average annual run-off is about 20 inches and
the run-off during the hydraulic season about 16 inches.

The run-off may also be approximately determined according to
Meyer’s method,! by determining the average annual evaporation and
transpiration and deducting these amounts from the precipitation. Meyer
has constructed a series of curves from which the mean monthly evapor-
ation may be determined if the mean monthly temperatures are known.
According to this method the mean annual evaporation at Barkerville is
13 inches and transpiration from vegetation 4 inches. This leaves a balance
of 19-47 inches as the mean annual run-off which is practically the same as
determined by the stream flow method. There are also some losses by
underground seepage, but they are probably very slight in the higher parts
of the region.

The estimate of 16 inches for the run-off during the hydraulic season
applies more especially to the higher parts of the region above 4,500 feet.
The run-off from the lower parts is less, because evaporation and under-
ground flow in the drift-filled valleys of the lower parts is much greater
than in the higher parts, where there is comparatively little drift and
where the slopes are steep, and is probably about 12 inches. The amount
of water available for hydraulicking or other purposes at any point in the
area may, therefore, be approximately determined. For example, the area
above the Stouts-Lowhee system of ditches is 306,000,000 square feet.
The total amount of water, taking the average run-off ag 13 feet, is
408,000,000 cubic feet. This amount is equivalent to 27-7 cubic feet per
second, or 990 miner’s inches throughout the hydraulic season.2 In order
to utilize all the water and to maintain a fairly uniform flow throughout
the hydraulic season it is, of course, necessary to have one or more reservoirs
to conserve the flood water. As the flow during the freshet is usually ten
times as great as during the low water summer stage, and in some years is
nearly thirty times as great, it is difficult to conserve all the flood water

ee Aye Run-off from Rainfall and Other Physical Data’’; Trans. Am. Soc. Civ. Eng., Mar. 1915, pp.
2A miner’s inch according to British Columbia statute is a flow of water of 1-68 cubic feet per minute.