The “divide” cut from the basin of the San Francisco to the upper lock, 14,200 feet in length, and with an average depth of 149 feet, is admitted to be a serious work; but with the neighbouring streams offering water at a high head for removing the surface earth by hydraulic mining, with a large plant of power drills worked by compressed air from the same source, and the use of modern explosives to loosen the rock, with a large proportion of the excavated rock to be used in the construction of the locks and the dam, and in pitching the slopes of the canal, a still larger quantity utilised in the construction of the harbour at Greytown, and convenient dumping-grounds for the remainder, the engineers claim that the work can be accomplished.
The following description of the proposed locks is taken from the report of Mr. Menocal, one of the engineers:—
“The locks proposed have a uniform length of 650 feet between the gates, and at least a width of 65 feet between the gate abutments. Locks Nos. 1, 2, 4, 5, and 6 have lifts of 26, 27, 26·4, 29·7, and 29·7 feet respectively. No. 3 has a lift of 53 feet, and No. 7, being a combination tide and lift lock, its lift will vary between 24·2 and 33·18 feet, depending on the state of the tide. It is believed that Nos. 1 and 7 will rest on firm, heavy soil, but timber and concrete foundations have been provided for in the estimates. Nos. 2 and 4 are estimated to rest on solid rock, and as for Nos. 5 and 6, the borings taken in 1873 show that stiff clay, compact sand and gravel will be met with. No. 3 is proposed to be cut out of the solid rock in the eastern slope of the ‘divide,’ by which the maximum strength will be secured with the least expense, concrete will be used only to the extent required to fill cavities, to give the proper dimensions to the various parts, and to give a surface to the blasted rock. The other locks it is proposed to build of concrete, and all of them, No. 3 included, will have a heavy timber lining in the chambers and bays, extending from the top of the walls to 15 feet below the low-water level.
“Cribs on firm bottom, or fender piles, when piles can be driven, have been provided at the approaches to the locks for the protection and better guidance of ships into the locks. Provision has also been made for making ships fast to the lock walls, so that the lines will, by means of floats, rise or fall with the ship, thus preserving the same tension on the lines while the vessel is kept in the axis of the lock. Each lock will be filled or emptied by conduits extending from the upper to the lower reach of the canal, and branch culverts connecting the main conduit with the lock chamber. The only operation required for either filling or emptying the lock will be, irrespective of the movements of the lock gate, the opening and closing of the upper and lower main culvert-gates. The time required to fill or empty lock No. 3, of 53 feet lift, will be fifteen minutes, and for the other locks an average of eleven minutes. The question of the best style of gates for these locks has been a subject of much consideration. It is desirable to combine strength, economy in construction, rapid and simple movements, facilities for repairs or for renewing the gates, and the least danger of accident by vessels entering or leaving the locks. The necessary machinery for moving the locks and culvert-gates, for hauling ships in and out of the locks, for electric lights, and other purposes, will be worked by hydraulic power furnished by the locks themselves.”
The chamber width of the locks will be 80 feet, so that these structures will contain almost any merchant vessel afloat.
In the plans proposed for the canal, not only have enlarged prisms been provided for, but large basins are proposed at the extremities of the locks. These basins, the enlargement of the canal at each end, with the lake, the river and the San Francisco basin, will permit vessels to pass each other without delay at almost every point on the route. Mr. Menocal states that—
In 22·37 miles, or 57 per cent. of the canal in excavation, the prism is large enough for vessels in transit to pass each other, and of a sectional area in excess of the maximum area in the Suez Canal; the remaining distance in which large vessels cannot conveniently pass each other is so divided that the longest is only 3·67 miles in length; with two exceptions, those short reaches of narrow canal are situated between the locks, and can be traversed by any vessel in less time than is estimated for the passage of a lock; consequently, unless a double system of locks be constructed, nothing will be gained by an enlargement of the prisms. The exceptions referred to are the rock-cuts through the eastern and western ‘divides,’ 2·58 and 3·67 miles, respectively, in length. The possible detention in the transit, due to those narrow cuts, which should not in any case exceed 45 minutes, would not justify the necessary increase of expense involved in an enlargement of the cross-section proposed. Both the bottom width and the depth of the proposed canal are larger than those of the Suez Canal.
In the lake and in the largest portion of the San Juan River vessels can travel almost as fast as at sea. In some sections of the river, and possibly in the basin of the San Francisco, although the channel is at all points deep and of considerable width, the speed may be somewhat checked by reason of the curves.
Estimated time of through-transit by steamer.
| Hrs. | Mins. | |
| 38·98 miles of canal, at 5 miles an hour | 7 | 48 |
| 8·51 miles in the San Francisco basin, at 7 miles an hour | 1 | 14 |
| 64·54 miles in the San Juan River, at 8 miles an hour | 8 | 4 |
| 56·50 miles in the lake, at 10 miles an hour | 5 | 39 |
| Time allowed for passing 7 locks, at 45 minutes each | 5 | 15 |
| Allow for detention in narrow cuts, &c. | 2 | 0 |
| Total time | 30 | 0 |