fall was only about 75 per cent. of the normal and moreover was less than in any other one of the twenty-nine years since the rain gage of the Rochester water works was established at Hemlock lake. The average run-off for the whole nine-year period as deduced from the incomplete gagings already described was 14.2 inches per year equivalent to a 14.2 inches flow from 1,000 square miles of x 0.884 factor x 950 sq. m.=994 12 months or say 1,000 cu. ft. per sec. The lack of precision in river gagings at Mount Morris appears to be all on the side of underestimating the flow, and the most probable value for yield in severest drought is 850 to 900 cubic feet per second. A flow averaging 1,000 cubic feet per second (equivalent to 1.13 inches run-off per month from the watershed of 950 square miles) could be delivered in many years without nearly emptying the reservoir, but a yield of 800 cubic feet per second can apparently be depended upon in what may be classed as the dryest year of the half century. In such an exceptionally dry year as 1895, or once in a lifetime, some curtailment of the power could be provided for, and some reduction in the number of hours, or the volume of water poured over the falls for scenic effect could be conceded, and I consider that the data in hand amply justifies the opinion that after making a fair provision for preserving the beauty of the cascades, and with the proposed reservoir flow line at say, elevation 1,210, there can be delivered from the Portage reservoir for power purposes, twenty-four hours per day, seven days in the week, throughout every year but the most extreme, 750 cubic feet per second. PROPOSED PORTAGE RESERVOIR. The maximum depletion caused by maintaining a constant draft of 800 cubic feet per second, partly for power, partly for scenic effect, would have been as shown in table below. |