It has been interesting to watch the water coming in and going out of the Atchafalaya Basin.

Of course, if you are one of the few who actually live inside the floodways, it is more than just interesting, it is probably taking most of your attention. But for those of us who love the Basin but benefit from its flood protection, the behavior of the water from the Morganza gates is a new study. After all, we have only seen it one time since the floodway system was built, most of us didn’t see much of it, and the lay of the land and water is much different than it was in 1973.

So i have been tracking the action for the past month and i plotted the water coming in and going out of the Basin. The following chart is a summary of the water movement in the Atchafalaya Basin Floodways, based on the numbers from the Corps of Engineers:
(Click the image to see a larger view. Click HERE to download a full size PDF)

Some things to note are the flow changes in the Red River as more water enters the Old River Control Structure and the filling of the Floodways as shown by the higher numbers for Total Inflow over Total Outflow. This is especially evident as the Morganza gates are opened and we see little increase in the Outflow as the water soaks in and makes its way down the path east of the Atchafalaya River.

Here is a different, simplified chart showing the relationships between stages at Butte LaRose and Morgan City and the water coming in to the Basin and going out at Morgan City.

Water normally takes a day to a day and a half to reach Butte LaRose from the Old River Control Structures and another day and a half to reach Morgan City. You can see that the opening of the Morganza gates and the diversion of about a fifth of the water through that side of the floodway system caused the timing to change considerably. The crests at Butte LaRose and at Morgan City were delayed by several days and the lag behind the water from Old River probably helped to lower the crests by spreading out the rise over time.

Whatever the reason, we are lucky that we didn’t see the predicted crests this time, and hopefully, we learned a little more about how the floodways work. Computer models and predictions are great, but nothing beats experience on the ground (or in the water.)

Charles Caillouet
Friends of the Atchafalaya

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