The delta has been changing since long before dams and levees. Thomas Hutchins (1730-1789) writes in 1784 at page 25:
Below New Orleans the land begins to be very low on both sides of the river across the country, and gradually declines as it approaches nearer to the sea. This point of land which in the treaty of peace in 1762, is mistaken for an island, is to all appearance of no long date; for in digging ever so little below the surface, you find water and great quantities of trees. The many beaches and breakers, as well as inlets, which arose out of the channel within the last half century, at the several mouths of the river, are convincing proofs that this peninsula was wholly formed in the same manner. And it is certain that when La Salle sailed down the Mississippi to the sea, the opening of that river was very different from what it is at present.
Historical Narrative And Topographical Description of Louisiana And West-Florida – 1784
An HISTORICAL NARRATIVE and TOPOGRAPHICAL DESCRIPTION of LOUISIANA, and WEST-FLORIDA, comprehending the RIVER MISSISSIPPI with its Principal Branches and Settlements, and the RIVERS PEARL, PASCAGOULA, MOBILE, PERDIDO, ESCAMBIA, CHACTAHATCHA, &c. , the CLIMATE, SOIL, and PRODUCE whether ANIMAL, VEGETABLE, or MINERAL, with directions for Sailing into all the Bays, Lakes, Harbours and Rivers on the North Side of the Gulf of Mexico, and for Navigating between the islands situated along that Coast, and ascending the Mississippi River, By THOMAS HUTCHINS, GEOGRAPHER TO THE UNITED STATES, PHILADELPHIA: printed for the author, and, sold by Robert Aitken, near the coffee-house, in Market-street. M.DCC.LXXXIV.