The Tangipahoa River after Isaac

For the past two years I have been studying and working in the Tangipahoa River watershed, primarily to target conservation areas that would protect buffer zones along the river to keep people out of reach of disastrous flooding. It’s hard to explain my work when people ask, but in a post-Isaac emergency like the potentially catastrophic flooding of the Tangipahoa River,  I think it is clear to everyone just how important it is to keep undeveloped green space along major rivers.

For the past 24 hours I’ve been hearing a lot of very vague warnings and evacuation orders. At first we were told “everyone along the Tangipahoa River has 90 minutes to evacuate,” that the river was going to rise 4-7 feet above its current level (which was already 3 feet over flood level, because of the incredible amount of rainfall. It is currently well-above flood stage at 22.5 ft.) Then it turned into “everyone within 2 miles of the river,” then 1 mile, then a half mile, and now Governor Jindal reassuring us that if the water on Lake Tangipahoa is released slowly into a nearby “wooded area,” then it will pose a much reduced risk of rapid water level rise than if the dam breaks. At times like this,  having a clear understanding of watershed dynamics is incredibly helpful. As it is, this flood event is going to rank as the 3rd highest water level on record. It could be more than that in the (increasingly unlikely) event of a dam breach.

First of all, those 2-mile, 1-mile and .5 mile distances given were arbitrary, and probably more related to “floodway” expectations (very quickly moving water) than potential flooding. Elevations along the river vary greatly. There may be residents on hills 10 feet or higher above catastrophic flood levels, who may be only a quarter of a mile or less from the overflowing riverbanks. Yet, people 5 miles or more out from the riverbanks may be at elevations so low that they may have to contend with backflowing streams and no drainage of additional rainfall for days. The further south you go, the wider and shallower the floodplain becomes– meaning greater risk for people further away from the river– until it eventually hits the 5-8 foot storm surges from Lake Ponchartrain.

The bridges across the river are nearly submerged already. The point of writing this is not to counteract the emergency orders, but to point out how incredibly dangerous it can be to live inside of a poorly understood watershed. Sure, we have FIRM maps and USGS river gauge data, but for residents and officials inside of Tangipahoa Parish, there is very little access to helpful information to determine who is really at high and low risk within our watershed when a major dam is at risk of being breached. We’ve had no comprehensive watershed studies to guide disaster planning, and as a result we have only vague and alarming, but not really helpful, emergency warnings.

Tangipahoa Parish has developed but has never fully adopted or implemented its Comprehensive Master Plan, which designates a mere 100-feet of green buffer zone along the river. That means that developers and landowners can continue to build extremely close to the banks of this relatively large local river. In 10-20 years, the number of people affected and the potential loss of lives to residents and their rescuers can increase dramatically in this rapidly-populating area. Information is not distributed explaining how fast moving water can quickly knock out a bridge or a roadway, and my husband was still able to get across the highway bridge this morning (though I certainly wouldn’t have recommended it!) in spite of water levels ABOVE THE LEVEL OF THE ROAD. The water is being held back by the concrete guards. Why hasn’t the parish closed off the bridges and roads within the advisory area? Certainly, people should be using common sense, but when information is lacking, why aren’t our public officials giving more guidance?

The truth is, we just don’t have enough understanding of our watershed.

We have the expertise and we have the capacity to begin this kind of study in Tangipahoa Parish, but it just hasn’t been done. The resistance seems mostly political. There is more incentive to continue encouraging growth than to take time to evaluate the safety of our current activities within the watershed. One big, final question I have is: Why is there an enormous dam at the head of a river that has had so little comprehensive analysis?

Okay, enough of that. Looking at elevations and historical information from the 1983 flood, I’ve put together a map of my property and the likelihood of flooding nearby if the dam breaks and the water does rise 4-7 feet or so. The boundaries are approximate, but behind our house there will be a 75+ acre lake where the old swamp used to be in the 1970’s, north of Bell’s Branch, before it was cleared and drained for pasture. The riverbanks tend to have high bluffs that can hold the water back for those living along the river, but the force of the water accelerates erosion and can eventually eat away at those bluffs pretty quickly. It’s possible with a big flood like this that the course of the river may actually change in some areas.

Right now I am “hunkering down” on the opposite side of the river, waiting it out. The river bridges are finally being shut down as I type because of high water, so it’s likely that I won’t make it back across for another 3 days to a week anyway– and even more if the bridges are knocked out entirely.

We did make it back to the property yesterday and so far everything has held up incredibly well in the storm. One of my fig trees is split three ways and lying on the ground, but I’m expecting it to recover. I’ll post some photos soon, and I’ll keep updating as there are new developments.

5 thoughts on “The Tangipahoa River after Isaac”

  1. Wow, Sara, thanks for the update and I hope you and your family fair well. We dodged Isaac over here in Panama City Beach, but you raise an issue that needs serious attention. For a brief time, there were mandatory evacuations in our neighboring county for low lying areas. Our family, located in other parts of the country, simply don’t grasp the geography here and I imagine it’s the same for many locals, who through no fault of their own, haven’t been adequately informed. They simply don’t understand or know if they are in a so-called low lying area. Your comprehension is far greater than mine, though I made an attempt to explain to my family why we weren’t at danger of flooding (this time) even though we are within 1,000 feet of the gulf. Seems a common theme of our modern culture, not knowing one’s place or carrying the stories of those who came before us. Great map btw and pretty sobering. You’re doing important work, especially given these challenging times.

    1. Yes, I would have definitely thought that you’d be at more risk only 1000 feet away, but I’m glad to hear that you were safe from the storm!
      Right before Isaac hit I was having nightmares of being in a house on the beach and the waves were rising higher and higher and eating away at the sand until there was little more than a few feet of sand between the house and the ocean. I had very similar dreams after Katrina, even though I wasn’t even along the Gulf Coast then.

      You know, not only do many people not realize the kind of danger they can be in during extreme flood events, but our local government has a very hard time getting out and informing people even when emergency evacuations are called. I imagine there were many people along the river that had no idea about the evacuation order, especially considering how many have lost power.

  2. I dont know you or your exact situation, but I stumbled across this entry when searching for some information for work. I felt compelled to calm some of your fears because of my experience in this area of science.

    Really not much to worry about at the lower end of the Tangipahoa River. The Lake Tangipahoa Dam is not a major dam by any means, although it isn’t insignificant. It’s failure could potentially cause damage or hurt persons who live directly below it, perhaps as far downstream as Osyka. During times of high water, the flood wave would be attenuated more than during low water. That means the flood wave wouldn’t make it as far downstream from the dam. Because the river was already flooding during the rains of Isaac, chances of seeing a significant rise due to a Lake Tangipahoa failure would have been very low downstream of Kentwood.

    The larger issue for your property would probably be just general river flooding from the river. Unfortunately, as you mentioned, many people are allowed to build too close to our area rivers in areas that may have flooded before. Also unfortunate – some of these people may not have lived in the area for a particularly long period of time and would not know much of impacts from past flooding. Such persons would also not be able to tie impacts in their local area to nearby river stage observations or National Weather Service forecasts.

    1. Thanks for the good information.

      “The Lake Tangipahoa Dam is not a major dam by any means, although it isn’t insignificant. It’s failure could potentially cause damage or hurt persons who live directly below it, perhaps as far downstream as Osyka.”

      This is the kind of information that would have been very helpful to know before or during the emergency warning, but as I said, there were some very alarming evacuation orders coming out in the beginning that gave the impression that this was a very serious situation for ALL of us along the river. Since many people didn’t have electricity at the time and had no way to research the dam if they weren’t already familiar with it, we were relying on these emergency evacuation orders that didn’t offer any kind of insight into the actual risk. Perhaps it’s better to be safe than sorry, and yes the river was already flooded so people should have been moving out anyway, but it just made me realize how seriously lacking the government and its citizens appear to be.

      Now, a lot of what I wrote was more in relation to general river flooding. I didn’t really expected the 4-7 foot rise to sustain all the way down here, but that is what we were told initially so I wanted to imagine it. The flooding in the image is actually what happened as a result of the 24.5 foot crest that we experienced. I found out some weeks later that the major reason for the 1983 flood hitting this area so hard was because of snags on the bridges that dammed up the river just south of here.

      I’m not fearful myself, but I still think it is dangerous that the local and state government doesn’t seem to know enough about the river to issue more precise and more accurate warnings in an emergency. If I didn’t have a cell phone and later internet access, things which many people didn’t have at the time, I would have had no way to find out anything about where the dam was or its size or whether it would affect me. The first warnings didn’t even say where it was. Literally, it was just this kind of message “a major dam is about to break on the Tangipahoa River, an emergency evacuation is issued for everyone within 2 miles of the river.” In the midst of a hurricane, that’s a pretty extreme warning compared to the reality of the situation, which we only found out later.

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