The Louisiana State Park Ranger with whom I spoke at Fort Pike explained that Forts Pike and Macomb were among the very first of the fortifications built under the Third System of American Seacoast Defense, so it was in these two forts that the US Army Corps of Engineers "made their mistakes." Since I've never seen a similar drainage system in place in any of the other forts that I've visited, I'm assuming this was one of those mistakes.