The Amite Canal

[chrispi]

In my 1776 ATL where the British win the Revolutionary War and Louisiana becomes an independent republic, I have the British dig a canal north of Baton Rouge, connecting the Mississippi to the Amite River, which flows into Lake Pontchartrain and bypasses New Orleans.

This canal fails, and a good deal of the Mississippi breaks through, diverting it eastward. What happens next? Any hydrologists here?