Scale of 4 feet to one inch
F. B. Tower.
Gimber.
Gate Chamber at the Head of the Aqueduct and Grade of the Water-way of the Aqueduct.
[Plate VIII]. is a longitudinal section through the tunnel and gate chamber at the head of the Aqueduct showing its connection with the Fountain Reservoir. This gate chamber is not in any way connected with the dam itself, but stands some distance from it, and the water reaches it by means of the tunnel which leaves the Reservoir above the dam and passes through the solid rock of the hill against which the masonry of the dam is built, a distance of over 200 feet. This tunnel descends into the Reservoir, so that the centre of it at the mouth is about 12 feet below the surface of the water; any floating substance cannot enter it, and during the winter season when the water is frozen over no obstruction can take place to the flow into the Aqueduct, and during the summer season the water will be drawn from a level where it is cooler than at the surface.
The gate chamber has two ranges, or sets of gates; one called regulating gates, and the other guard gates: the regulating gates are made of gun metal, and work in frames of the same material which are fitted to stone jambs and lintels: the guard gates are made of cast iron, and work in cast iron frames also attached to stone jambs and lintels. The gates are all managed by means of wrought iron rods attached to them, having a screw formed on the upper part on which a brass nut works, being set in a cast iron socket-cap.
The bottom of the water way, of the Aqueduct, where it leaves the gate chamber is 11.40 feet below the surface of the Fountain Reservoir, and 154.77 feet above the level of mean tide at the city of New-York. The following table shows the length of the Aqueduct as it is divided into different planes of descent, from the gate chamber at the Croton dam to the gate chamber at the Receiving Reservoir on the Island of New-York. Commencing at the south side of the gate chamber at the Croton dam,
| The 1st plane of Aqueduct extends | 26099.72 ft. or 4.943 miles, and the descent | 2.94 ft. |
| The 2d plane of Aqueduct extends | 148121.25 ft. or 28.053 miles, | 30.69 ft. |
| Length of pipes across Har. River, | 1377.33 ft. or 0.261 miles. | |
| Diff. of level betw’n extremes of pipes | 2.29 ft. | |
| The 3d plane of Aqueduct extends | 10733.14 ft. or 2.033 miles, | 2.25 ft. |
| Length of pipes across Manhat. valley, | 4105.09 ft. or 0.777 miles. | |
| Diff. of level betw’n extremes of pipes | 3.86 ft. | |
| The 4th plane of Aqueduct extends | 10680.89 ft. or 2.023 | 1.60 ft. |
| 201117.42 ft. — 38.090 miles | 43.63 ft. |
Making the whole distance from the gate chamber at the Croton dam to the gate chamber at the Receiving Reservoir 201117.42 feet, or 38.09 miles, and the whole descent 43.63 feet.
The descent on the first plane is about 7⅛ inches per mile.