Hi Bob I think that the main confusion between the text and the maps in the North & South article is that even though the Bayou Teche meanders in a West to East direction in the Bisland area, the text labels the area North of the bayou as the "East Bank" and the area South of the bayou as the "West Bank". This seems to be a common practice in Louisiana. In New Orleans you can drive due south on a bridge over the Mississippi river and end up on the "West Bank".
I visted the battlefield myself several years ago and found that the area North of the Teche, where the 31st Mass. fought, was occupied by large open sugar cane fields, bordered by trees along the Teche and trees and the Grand Lake Levee to the North. If you visited the area at this time of the year when the cane fields are not yet planted and growing, you could walk the same fields that your ancestor advanced throught and cuss the same ridged cane rows that made the advance difficult.
Have you read the O.R. battle report of Col. Hopkins, who commanded the 31st Mass. at Bisland. You can find the Official Records of the Rebellion online at Cornell University's MAKING OF AMERICA website