The following figures show the estimated minimum dependable supply from the various proposed sources with net useable storage as specified in the preceding table.
Mgd 1st stage or Present Project Hemlock Lake Reservoir at new dam, excluding Canadice Lake but including Canadice Outlet, the area tributary to the Lower Basin, and Livonia Creek ......................... 32.5 Canadice Lake ................................................. 7.5 Total from Hemlock areas .............................. 40.0 2nd stage Calabogue area added, including three smaller areas ........... 45.0 3rd stage Cohocton areas added - Total net estimated supply ............. 50.00
It is always desirable to provide some factor of safety in estimating the ultimate dependable yield from a water supply system dependant on storage. A factor of safety is best available in the form of reserve storage. This can easily be provided by adopting as the dependable yield of a given project a quantity of flow somewhat less than the computed yield, thereby providing a certain amount of reserve storage which will remain in the reservoir and still be available at the end of the longest dry period.
These estimates have been made up in such a manner as to allow 10 % reserve storage in the new Hemlock Reservoir. This is equivalent to roundly 1,500,000,000 gallons of storage, which would not be used even in the driest years but would be held in reserve or emergencies.
All structures would be designed to permit draft of the Hemlock Reservoir to elevation 381.00. The minimum draft level, barring such unforseen conditions, would be elevation 384.00. The reserve storage lies between elevations 381.00 and 384.00.
The figures show a dependable yield on completion of the first stage of the project of 40 mgd, as compared with 31 mgd estimated yield from the Hemlock-Canadice system as now developed. This increase arises in three ways:
1. From additional storage of 4.12 billion gallons storage in new Hemlock Lake proper.
2. From additional storage of 1.53 billion gallons in the new Hemlock Lake Reservoir.
3. By bringing into the new reservoir the flood and melting snow runoff from 9.25 square miles of additional area.
The figures on yield given in this report are based on the use of much more complete and extensive data of runoff etc. than have been either available or used in any previous estimates of yield of this system. The results, however, check closely previous estimates as to the yield of the present system and they are therefore chiefly due to the above named three causes rather than to differences in the data or computations.
The figures given for the new dependable yield at the end of the second and third stages of development, i.e. with the Calabogue and Cohocton areas added, are necessarily tentative as the surveys not completed.