Of the above distance, the first ninety-one miles, or from San Carlos to half a mile below the Serapiqui River, Colonel Childs proposed to make the river navigable by excavating its bed, and by constructing dams, to be passed by means of locks and short canals; the remaining twenty-eight miles of the canal to be constructed inland, or independently of the river. Of the whole fall, sixty-two and a half feet occurs on that portion which it is proposed to improve by dams, and on which there were to be eight locks, and the remaining forty-six and a quarter feet occurs on the inland portion of the canal, on which were to be six locks—fourteen locks in all.
Colonel Childs proposed to place the first dam at the head of the Castillo Rapids, a distance of upward of thirty-seven miles from the lake, and to pass the rapids by means of a lateral canal. By means of this dam he proposed to raise the water, at that point, twenty-one and a half feet, and the entire level of Lake Nicaragua five feet above its lowest stages, or in other words, to keep it at high-water mark. The fall at this dam would be sixteen feet. He proposed also six other dams, four of eight feet fall, one of fourteen and a half feet, and one of thirteen and a half feet. Between all of these there would be more or less excavation in the bed of the stream, sometimes in earth, and often in rock.
Colonel Childs proposed further to improve the harbor of San Juan by moles, etc., and to construct an artificial harbor in connection with it of the capacity of thirteen acres.
In respect of the amount of water in the San Juan, we have some interesting statistics. This amount, of course, varies greatly with the different seasons. The quantity of water that passed from the lake at its lowest stage, on the 4th of June, 1851, was 11,930 cubic feet per second. The greatest rise of the lake is about five feet. When it stood at 3.43 feet above its lowest level, the flow of water was 18,059 cubic feet per second, being an increase of about fifty per cent. Supposing the same ratio of increase, at high lake the amount of water in the river would be doubled.
The river receives large accessions from its tributaries. Below these, and above the point of divergence of the Colorado, flowing direct into the sea from the San Juan, which falls into the harbor of the same name, the flow of water was 54,380 cubic feet per second, of which 42,056 passed through the Colorado branch into the ocean, and 12,324 through the San Juan into the port.
Dimensions of the Proposed Canal.—Where the excavation is in earth, Colonel Childs proposed (and all his estimates are founded on these dimensions) that the canal shall have a depth of 17 feet; that it shall be 50 feet wide at the bottom, 86 feet wide at 9 feet above the bottom, and 118 feet wide at the surface of the water. Where the excavation is in rock, the canal is to be 50 feet wide at bottom, 77 feet at 9 feet above bottom, and 78⅓ feet at the surface of the water.
Length of Proposed Canal.—The total length of the line proposed by Colonel Childs, from San Juan del Norte on the Atlantic, to Brito on the Pacific, is 194⅓ miles, as follows:
| Miles. | |
| Canal from port of San Juan to its point of intersection with the river, near the mouth of the Serapiqui | 28.505 |
| Slack-water navigation on the San Juan River, from the above point to San Cárlos, at the outlet of the lake | 90.800 |
| From San Cárlos, across Lake Nicaragua, to the mouth of the Rio Lajas | 56.500 |
| From mouth of Rio Lajas to Brito | 18.588 |
| Total, as above | 194.393 |
Estimated Cost.—The cost of the work is estimated by Colonel Childs in detail. The recapitulation, by divisions, is as follows:
| Eastern Division (i. e., from port of San Juan to lake) | $12,502,346 |
| Middle Division (through lake) | 1,025,676 |
| Western Division (from lake to Pacific) | 13,896,603 |
| $27,424,625 | |
| Add, for contingencies, 15 per cent | 4,113,693 |
| Total estimated cost of canal | $31,538,318 |