The surveys and investigations have resulted in the formulation of a project which retains the present Hemlock system and provides increased storage and tributary drainage area sufficient to maintain a dependable supply of at least 50 mgd.
The project contains various items which have hereto been considered separately but the result differs from that of previous studies by bringing together all of the salient points requiring consideration in a single coordinated project, fitted into the existing Hemlock supply system. Such a program is necessary at this time since some steps must be taken immediately to relieve the situation created by war conditions, and the steps to be taken depend to a considerable degree on the longer range project to be adopted.
The investigations have been carried far enough so that the controlling features of the main project for increased supply can be definitely outlined. Field surveys are still in progress and much further work is required before detailed plans can be prepared for some of the structures required. In particular, consideration of the question of relining or replacement of Conduit II must be deferred until the relining of Conduit I (now in progress) and other conditions permit un-watering of Conduit II section by section.
Various figures given in this report, particularly as to elevations, flow lines etc., are derived from existing maps and reports, and while believed to be substantially correct, they are subject to revision upon completion of field surveys and detailed studies.
For purposes of comparison a brief outline of salient features of some other projects heretofore considered is given later.
The main features of the project are shown on Figs. 1 and 2.
F1,2)
Referring to fig.1, a new dam would be constructed about one-quarter mile upstream from the highway crossing Hemlock Lake Outlet at the village of Hemlock. This dam would have a fixed spillway at crest elevation 403.00 and would provide additional storage in two ways:
1. By increasing the depth of flowage in Hemlock Lake from elevation 397.5, the present maximum, to 403.00.
2. By creating an additional storage basin, designated the "Lower Basin," between the present Hemlock Lake and the new dam. This would provide about 1.53 billion gallons additional storage.
The present Hemlock Lake dam would be raised and retained as a partition wall between Hemlock Lake proper and the lower basin, so that water could if desired be drawn from either basin.
The present Gatehouse No. 2 at Hemlock Lake would be retained, together with the 6-foot diameter brick main supply tunnel leading therefrom to overflow No. 1.
In addition a new Gatehouse would be constructed at the new dam and a new main supply conduit would be built therefrom to Overflow No. 1, providing increased flexibility of supply to the present and future conduits leading from Overflow No. 1 to the City. The new main supply conduit would have a capacity to deliver about 65 mgd at Overflow No. 1. The supply could be drawn through either main supply conduit as long as the demand did not exceed 40 mgd. The new supply conduit would have a capacity to take care of fluctuations in demand, with an ultimate water consumption of 45 mgd.
Detailed topographical surveys have been made of the site of the lower basin and topographic surveys and underground explorations have been made at the dam site. The higher portion of the dam and the foundation of the new gatehouse would be on rock and a fixed spillway would be provided of sufficient length to avoid the use of manually controlled stop-logs or flashboards. The increased storage provided by the new dam would be used in part to impound waters now wasted and thereby increase the supply from the present Hemlock drainage basin. It would be used to provide regulation for additional water brought in from adjacent areas.
Excluding Canadice Outlet, there is a natural drainage area of 9.25 square miles tributary to Hemlock Outlet between Hemlock Lake and the proposed new dam and this additional area would become directly tributary to the lower basin.
Canadice Lake dam would be reconstructed and a new fixed spillway provided at the west end, avoiding manual operation during floods. The flow line would be raised 3 feet or from elevation 1096.00 (USGS) to elevation 1099.00 (USGS).
Provision would also be made to draw Canadice Lake down to elevation 1081.00 (USGS), providing a total storage draft of 18 feet as compared with the present use of 6 feet of storage in Canadice Lake. This would provide complete regulation of the runoff from 12.6 square miles of area tributary to Canadice Lake and avoid the use of storage in Hemlock Lake to regulate Canadice Lake yield, as has been done heretofore.
Outflow from Canadice Lake would flow down from Canadice Outlet into the lower basin of Hemlock Reservoir. Use of the present diversion dam and conduit leading from the diversion weir at Beams dam on Canadice Outlet to Hemlock Lake would be discontinued. These are the only structures appurtenant to the present Hemlock system which would not serve a useful purpose in conjunction with the enlarged Hemlock supply system.Regulation of the runoff of the 5.8 square miles of area tributary to Canadice Outlet below Canadice Lake would be accomplished at present through the use of part of the additional storage provided by the lower Hemlock basin.