The inflow of the lake is derived chiefly from three rivers, and is susceptible of very exact determination. Thorough measurement has not yet been made, but there has been a single determination of each river and minor stream, and a rough estimate can be based on them. The Bear and the Weber were measured in October, 1877, and I am led by the analogy of other streams and by the characters of the river channels to judge that the mean volume of the Bear for the year was twice its volume at the date of measurement, and that of the Weber four times. The mean flow of the Jordan can be estimated with more confidence, for reasons which will appear in a following chapter. The “supply from other sources” mentioned in the table includes all the creeks that flow from the Wasatch Mountains, between Draper and Hampden, together with the Malade River, Blue Creek, the creeks of Skull and Tooele Valleys, and the line of springs that encircles the lake. +---------------------------------------------+----------+-----------+ | | Measured | Estimated | | |volume in |mean volume| | Rivers, etc. | feet per | in feet | | | second. |per second.| +---------------------------------------------+----------+-----------+ |Bear River, measured October 4, 1877, | | | | at Hampden Bridge | 2,600 | 5,200 | |Weber River, measured October 11, near Ogden | 500 | 2,000 | |Jordan River, measured July 8, near Draper | 1,275 | 1,000 | |Supply from other sources | -- | 1,800 | | +----------+-----------+ | Total | -- | 10,000 | |Deduct the water used in irrigation | -- | 600 | | +----------+-----------+ | Remainder | -- | 9,400 | +---------------------------------------------+----------+-----------+ The result expresses the mean inflow to the lake in 1877, and is probably not more than 25 per cent. in error. The total inflow for the year would suffice to cover the lake to a depth of 60 inches. In the same year (or from October, 1876, to October, 1877) the lake fell 6¹⁄₂ inches, showing that the loss by evaporation was by so much greater than the gain by inflow. The total annual evaporation of inflowing water may therefore be placed provisionally at 66¹⁄₂ inches. If we add to this the rain and snow which fall on the lake, we deduce a total annual evaporation of about 80 inches of water; but for the present purpose it will be more convenient to consider the former figure.