Fig. 11.—Canal and Power-house on St. Joseph River, Buchanan, Mich.
A similar location was selected for the station at Great Falls, on the Presumpscot River (see cuts), whence electrical energy is delivered in Portland, Me. Four steel penstocks, a few feet long and each eight feet in diameter, bring the water in this case from the forebay section of the dam to the wheel cases in the power-house.
Fig. 12.—Power-house on Hudson River at Mechanicsville.
Where the power-station is located at the foot of the dam, as just described, that part which serves as a forebay wall usually carries a head gate for each penstock. The overfall section of a dam may give way in cases like the two just noted without necessarily destroying the power-station, but in times of freshet or very high water the station may be flooded and its operation stopped. The risk of any such flooding will vary greatly on different rivers, and in particular cases may be very slight. Location of the generating station close to the foot of the dam at one end obviously avoids all expense for a canal and cuts the cost of penstocks down to a very low figure.
Such locations for stations are not limited to falls of any particular height, and the short penstocks usually enter the dam nearer its base than its top and pass to the station at only a slight inclination from the horizontal. At Great Falls, above mentioned, the head of water is thirty-seven feet.
A short canal is constructed in some cases from one end of a dam to a little distance down-stream, terminating at a favorable site for the electric station. Construction of this sort was adopted at the Birchem Bend Falls of the Chicopee River, whence energy is supplied to Springfield, Mass. These falls furnish a head of fourteen feet, and the water-wheels are located on the floor of the open canal at its end. The power-station is on the shore side of this canal, and the shafts of the water-wheels extend through bushings in the canal wall, which forms the lower part of one side of the station, to connect with the electric generators inside.
This rather unusual location of water-wheels has at least the obvious advantage that they require no room inside of the station. Furthermore, as the canal is between the station and the river, any break in the canal is not apt to flood the station.
