2. The material along and on the sides of the Pontchartrain route is, with the exception of a small stretch, more tenacious, and contains, in general, a greater proportion of sand than in the case of the neighboring channels mentioned.
The channel could therefore be more easily maintained.
Engineers estimate that a channel with a 300-foot bottom would be needed. On the south shore of the lake, the side slopes should be on the 1 to 3 ratio, with provision for a 1 to 5 ratio at the end of five years. Dumped on shore, the material would reclaim considerable frontage, and eliminate the re-deposit of this material in the channel.
Through the remainder of the route, the original excavation should be made with side slopes on the 1 to 5 ratio, with provision made for a 1 to 10 ratio in five years.
The dredging of the 75 miles of the Pontchartrain Channel would amount to 97,200,000 cubic yards, it is estimated by engineers. The cost would be around $10,000,000. The annual maintenance, during the first five years, would amount to 8,880,000 cubic yards—an estimate based on a comparison with the other channels into the Gulf, and the character of the material to be excavated. This estimate is considered large—but even at that, it is only 118,400 cubic yards a mile a year, and the cost would be about $750,000, according to Colonel Dent. After five years, it would be less.
Another proposed route, investigated by Colonel Dent, is through Lake Borgne. A canal some miles in length, through the marsh, would connect the lake with the Industrial Canal. This route has considerable maintenance advantages over the Pontchartrain route. The character of the bottom in Borgne is more or less the same as in Pontchartrain.
Sooner or later, one of these channels will be built by the government. That it has not already been begun is due to the fact that the Canal has not yet been completed, and the expected development has not taken place. But there is no doubt that it will.
TYPICAL BRIDGE ON CANAL
