emptied below elevation 1,120, thus leaving at all times in view from the dam a lake, half a mile or more in length upstream and of substantially the full width between the bluffs, this reserve being provided for as a pleasing feature in the landscape and with no noteworthy detriment to the storage reserves for power and flood control. The intake for the proposed power tunnel to be at a still higher level, so as to cause a reserve in even the most severe drought sufficient for a flow of from 100 to 200 cubic feet per second during the hours of daylight for about 100 days, which cannot be withdrawn for power.

Two alternative sites for a power-house have been surveyed, both of which are downstream from the lowest limit of the Letchworth Park. Up to the present time, study has been mainly concentrated upon the one farthest downstream, since this promises much larger power and greater ultimate economy. This is about three miles down the course of the river from the lower fall and far beyond the limits of the park.

At this lowest site, the river level is about elevation 665, and as the ordinary working level in the proposed great lake above Portage would be about 1,190, the gross fall is 525 feet.

This is about 90 feet greater than the gross fall available at the alternative site one-half a mile downstream from the lower falls, but a part of this difference would be lost by friction in the greater length of tunnel.

The intake for the proposed tunnel is about three-fourths of a mile away from the dam site, going easterly along the north shore of the basin, and the tunnel nowhere runs within about half a mile of the outside limits of the Glen Iris Park.

This tunnel is proposed to be of about 15 feet in diameter, and although borings along its course have not yet been made, it appears probable from a study of the outcrop of ledge, that by keeping the tunnel level down nearly to the power-house elevation, excellent rock will be found all the way. An exceptional structure for a surge shaft is proposed at the downstream end of this long pressure tunnel.

Much study has been given to its design, and it is believed that by use of the form designed all trouble in governing the speed of the turbines or in troublesome waves in the long conduit or in waste of water, can be avoided, and that the full reservoir head can be made available for power, less, of course, the friction loss.

YIELD OF DRAINAGE AREA ABove Portage, WITH STORAGE.

The drainage area above Portage contains substantially the same number of square miles as that above Conklingville, but yields much less water, because of the rainfall in this region being smaller and also because of the proportion of the rainfall lost by evaporation being larger, due to the general deforestation of the country for agricultural purposes.

A careful study of the rainfall records and of the gagings of stream flow, made by the mass curve method as already described, indicates that the mean flow of water available for power purposes after making a reservation for scenic purposes at the Genesee Falls, will be only about one-half as great as at Conklingville.

On the other hand, the fall of water is more than twice as great, with a result that the total output of electrical power from the Portage reservoir available for delivery at Rochester, Mount Morris or elsewhere within a radius of fifty or seventy-five miles, is somewhat greater than that available from the proposed Sacandaga power-house.

At the Portage reservoir as in the case of the Sacandaga reservoir, it is not a necessity that the tunnel and power-house be built at the same time as the dam and storage reservoir. They could be built five or ten or twenty years later or whenever desired, and meanwhile the State could utilize the storage reservoir for the increase of present water powers at Mount Morris and Rochester under a proper payment, and to a very noteworthy extent the reservoir would meanwhile also serve for flood control, and during this period while so used, all the water of the river would pass over the Genesee Falls, and the volume flowing over the falls during the vacation or tourist season from July first to October first, would be far greater than under present conditions.

Our estimates by the mass curve method as already described, and after some consideration of the conditions that affected the accuracy of the stream flow gagings, show that a total yield of 800 cubic feet per second, twenty-four hours per day, seven days in the week, may be relied on throughout years as dry as 1895, and a study of the rainfall records indicates that no year of smaller rainfall or smaller stream flow than 1895 has occurred on the Genesee river during the historic period.

ESTIMATE OF POWER.

The power that the storage would add at Mt. Morris and Rochester has been already estimated on page 194.

The power that could be made available in the projected Portage powerhouse at site B., the lower site, is estimated as follows:

Ordinary or mean level in reservoir..

Water level at tailrace...

Gross fall.

Tunnel about 34 miles in length or about 20,000 feet. Probable average loss of head in tuunel, etc., not over.

Ordinary net fall.

To be safe call this 500 feet.

If average available flow in a series of dry years after allowing water for scenic purposes as described on p. 188 is 750 c. f. s. the power will be 750 x 62.4 x 500 x 75%

power.

550

abt. 32,000 net twenty-four hour, seven-day horse

With a load factor of 40 per cent., this becomes for use in ordinary working hours, 80,000 mechanical horse-power on the turbine shaft.

At 95 per cent. efficiency, this would generate 56,800 kilowatts, and at 85 per cent. efficiency of conversion and transmission, this would deliver at the consumers end 68,000 horse-power in ordinary working hours for manufacturing purposes throughout a dry year; with a larger diversion of water for scenic purposes at Genesee Falls, the yield of power would be correspondingly less; 700 cubic feet per second would yield 63,500 horse-power.

Since as already stated, the estimates of flow of river are probably somewhat low, it appears entirely conservative to speak of this project as capable of yielding 32,000 horse-power of twenty-four hour seven-day power on turbine shaft, or of delivering 65,000 horse-power to consumers under a 40% load factor.

CONSTRUCTION PROPOSED FOR PORTAGE DAM.

The accompanying drawings show the general characteristics of the structures proposed so fully that little further description is necessary.

A system of drainage for the interior of the dam is provided, consisting of a series of wells about two feet in diameter spaced about fifteen feet apart, rising from near the bottom to above the water level and communicating with galleries at top and bottom, all ordinarily closed to circulation of air but arranged so that access could be had for inspection. These wells would be formed by molded blocks of porous concrete imbedded as the building of the dam progresses. They are spaced a substantial distance back from the water face and intended to intercept any of the little leakage that is likely to seep through concrete under great pressure, here and there, however great care be taken. The purpose of intercepting this is to prevent possibility of stresses of hydrostatic uplift, particularly when escape of moisture from outer face might be sealed by frost. This dryness of outer face tends to its durability under frost action and avoids the unsightly appearance and discoloration due water, often seen on high masonry dams.

The sluiceway gates are planned on the Venturi principle in a novel manner in order to save in cost, to make them easier and quicker to operate and in order to quiet the discharge.

It is proposed to operate them on the hydraulic press principle, obtaining the pressure from the reservoir. Since gates operating under a head so great as given by the full reservoir and without back pressure are liable to chattering or to destructive vibration, a special design of gate valve is proposed in which it is believed quiet action can be secured by avoiding projecting lips and by supporting the seat in a novel manner.

The outer base of the dam is to be shielded from extreme temperature strains or frost action by blanketing it with earth and riprap, and a molded base course is planned for architectural effect.

There is an admirable opportunity to build the spillway channel on such declivity and with such a steep slope that its gorging by ice or by flood debris will be impossible and that the destructive energy of the great volume liable to come through it in a great freshet, can be largely absorbed by eddies or water cushions.

If it should later be deemed allowable to build at the more economical site nearer the upper falls within the park limits, proposed by Mr. Rafter, I would recommend adherence to the general design shown in these drawings rather than the earlier designs.