Thomas Jefferson Papers

From Thomas Jefferson to Henry Dearborn, 12 May 1808

Monticello May 12. 08.

Dear Sir

My journey & two days detention on the road by high waters gave me time to reflect on our Canal at New Orleans, on which I will therefore hazard some thoughts.

I think it has been said that the Misipi at low water is many feet lower, opposite N.O. than lake Pontchartrain. but the fact is impossible, being in contradiction to the laws of nature. two beds of dead water connected with the same ocean, in vicinity to one another, must each be in the level of that ocean, and consequently of one another. altho Pontchartrain recieves the Amite & some other small streams, they probably do little more than supply it’s evaporation. no doubt however that the lake must recieve the small ebb & flow of the sea. The Missipi on the contrary, even at it’s lowest tide, always flows downwards to & beyond it’s mouth. it must then, at N.O. be one, two, or three feet higher than the sea, & consequently than L. Ponchartrain.

If a simple canal were cut from that of Carondelet to the Misipi, without lock or gate, there would be two risks, 1. that in high water of the Misipi the current would be too strong for a gunboat to ascend or descend. this might perhaps be remedied by the draught of horses. 2. the force of such a current (unless the whole canal were lined with brick or masonry) might convert the canal into a Bayou of unknown size, & involve N.O. in it.

On the whole I suspect our plan is pretty obvious. Suppose we want 6. f. water, make a canal of that depth below the lowest ebb of Pontchartrain from the lake to where the lock is to be placed. then bring a canal from the river to the lock, the depth of which shall be 6. feet below the lowest water of the Misipi ever known. at the lock there will be a descent, suppose of 1. 2. 3. feet or any other number. the lock remedies that.

If the lock were near the lake, it would lessen the work by giving nearly the whole length to the shallowest canal, and it would probably be in a more tranquil & safe situation. But it might be inconvenient, perhaps unsafe to the sides of the Misipi canal to permit such a depth of water as would be in it thro’ it’s whole length at the time of the high water of that river. of the best position therefore of the lock the Superintendant must judge on the spot, as he must indeed of the correctness of all the preceding conjectures, formed without a knolege of the localities. they are hazarded merely to give us some fixed notions of the nature of the enterprize, and are submitted to your consideration. I salute you with affectionate respect.

Th: Jefferson

PHi: Daniel Parker Papers.

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