Archive for 2011 Mississippi River Flood
By Alisha Renfro, Staff Scientist, Restore the Mississippi River Delta Coalition, National Wildlife Federation
As the Mississippi River high water event continues, the U.S. Army Corps of Engineers will soon open the Bonnet Carré Spillway, and potentially the Morganza Floodway, to help relieve pressure on river levees and prevent catastrophic flooding. During high-water events like this one, the river contains more water and carries more sediment than usual. Without restoration projects like sediment diversions in place to capture sediment, much of this essential component for restoring our coast is lost. In the future, when sediment diversions are in place, we’ll be able to utilize the increase in sediment carried by the river during high water events and capture it for coastal restoration. This blog is the first in a series that examine management of the Mississippi River for flood protection and the opportunities that exist to do so for coastal restoration.
Unusually heavy winter rainfall throughout much of the Mississippi River’s drainage basin has led to early flood conditions on the Mississippi River. Deaths of at least 29 people and loss of property in Illinois, Missouri, Arkansas and Oklahoma are a stark reminder of how dangerous floods can be.
On the lower Mississippi River, the Mississippi River and Tributaries (MR&T) project uses levees and floodways, among other measures, to manage river floods, like the one happening now, to protect people and property.
Prior to the disastrous 1927 flood, attempts to prevent flooding along the lower Mississippi River relied on levees along the river built to withstand the previous flood of record. The MR&T project, authorized through the Flood Control Act of 1928, is a more comprehensive U.S. Army Corps of Engineers’ flood control program. It relies on levees along the river to control flood flows, floodways to lessen pressure on critical points in the river levee system, improvements and stabilization of the river channel for navigation, and improvements to major tributary drainage basins, such as dams and reservoirs. Combined, the features of the MR&T system are designed to handle the largest flood that is reasonably expected to occur, known as “project flood.”[i],[ii]
In Louisiana, river floods rely on protection provided by levees along the Mississippi and Atchafalaya Rivers, the Old River Control Complex, the Bonnet Carré Spillway and the Morganza and West Atchafalaya Floodways.
- The Old River Control Complex is designed to send 30 percent of the combined flow of the Mississippi and Red Rivers down the Atchafalaya River, and the remaining 70 percent of the flow down the main stem of the Mississippi River. During this current river flood, the U.S. Army of Engineers began operating the Old River Overbank Structure on December 30 to reduce the risk of damage to Old River Control Complex sill structures.
- The Morganza Floodway is operated during flood events to shunt excess floodwater from the Mississippi into the Atchafalaya Basin. This structure has only been operated twice, 1973 and 2011, since construction was completed on it in 1954. The U.S. Army Corps of Engineers is monitoring the river gage at Red River Landing to determine if this structure will be needed during the current high water event.
- The Bonnet Carré Spillway is located upriver of New Orleans. When opened, this structure can shunt up to 250,000 cubic feet per second of sediment-laden water from the river into Lake Pontchartrain, to reduce pressure on the river levees by keeping water flow below 1.25 million cubic feet per second. The U.S. Army Corps of Engineers will open this structure during this flood event beginning on Sunday, January 10.
- The West Atchafalaya Floodway is the last feature of the flood control system and has not been used to date.
The MR&T project has been successful in managing river flood risk during several flood events, most recently in 2011. The water levels in the river are expected to continue to rise over the next week and features of the project, such as the Bonnet Carré Spillway, will be used to manage the floodwaters and protect people and property along the lower Mississippi River.
Up next in this blog series, Alisha Renfro will examine sediment levels in the Mississippi River during high flood conditions and what implications this could have for coastal restoration.No Comments
This was originally posted by Environmental Defense Fund on EDF Voices.
By Estelle Robichaux, Restoration Project Analyst, Environmental Defense Fund
Soon after my flyover of the Mississippi River Delta, I joined Dr. John Lopez of the Lake Pontchartrain Basin Foundation (LPBF) on a boat ride down the Bohemia Spillway to Mardi Gras Pass. As we sped down the spillway canal, beautiful swamp lilies and purple morning glories popped out against a backdrop of lush, green plants. Once we reached our destination, we saw an incredible number of birds: Laughing Gulls, Snowy Egrets, Great Blue and Tricolored Herons – just to name a few. This, along with an increase in the number of river otters and beavers observed, is a good indicator that there are healthy fish populations in the area.
Thirty-five miles southeast of New Orleans, Mardi Gras Pass is the Mississippi River’s newest and naturally evolving “distributary,” a channel of water that flows away from the main branch of the river. This new distributary began forming during the spring flood of 2011, when the water level of the Mississippi River was so high that it flowed over the natural levee in this area. When the floodwaters receded, Dr. Lopez and his team of scientists noticed two breaches in the embankment. These breaches continued to widen and deepen and soon, right around Mardi Gras Day 2012, the breach was complete. The Mississippi River was once again connected to the surrounding wetlands, allowing freshwater and land-building sediment back into the area.
Louisiana has lost 25% of its coastal land area since 1930 and continues to lose land at an alarming rate – one football field every hour, on average. Man-made levees along the Mississippi River cut off many small distributaries, like Mardi Gras Pass, from the wetlands in the floodplain of the river and have contributed to this massive wetland loss. Our team here at EDF works with partner organizations, including the Lake Pontchartrain Basin Foundation, as part of the Mississippi River Delta Restoration Coalition, which has a vision of reconnecting the Mississippi River to its delta to help protect people, wildlife and jobs in coastal Louisiana.
To address the complex, yet urgent need for coastal restoration in Louisiana, the state legislature unanimously passed the 2012 Coastal Master Plan. This plan is a long-term, science-based restoration program that includes nearly 250 restoration projects such as barrier island restoration, marsh creation, establishment of oyster barrier reefs and sediment diversions that will help rebuild Louisiana’s disappearing coast.
Restoring our coast, restoring my hope
One of the principal guidelines for restoration under the Coastal Master Plan is to address the root causes of land loss by using the natural power of the Mississippi River to build land at a large scale. Sediment diversions, a central component of the plan, embody this principle because they are designed to mimic the natural stages of the river and carry sediment to the areas of coastal Louisiana that need it most. By operating diversions at times of high water flow (like during a flood), large amounts of sediment can be diverted. It will then settle out in the wetlands and shallow bays, eventually building land mass in vulnerable coastal areas.
In a way, Mardi Gras Pass is a naturally occurring ‘pilot project’ of a sediment diversion. Knowledge gained from studying this area can tell us about the land-building properties, as well as the short-term effects, of sediment diversions. To learn more about this, LPBF scientists are studying how the reintroduction of freshwater and sediment to the spillway area is changing the wetlands and affecting wildlife populations.
Swift currents and downed trees along the edge of the flooded forest can make navigating Mardi Gras Pass somewhat treacherous, but we, in a trusty 14’ skiff, maneuvered through the channel and onto the Mississippi River for a brief but thrilling cruise.
This is what it means for the river to be connected to its floodplain, I thought as we emerged out onto the open water, this is what this ecosystem is supposed to be like.
Although I grew up only a few miles from it, this was the third time in my life I had been out on the Mississippi River and the first time it was in a boat small enough that I could reach down and touch its muddy waters. As our tiny boat circled out in that mighty river, despite the heat and the midday sun, I had goose bumps.No Comments
By Alisha A. Renfro, Ph.D., Staff Scientist, National Wildlife Federation
This year, drought conditions throughout most of the country have left the Mississippi River flowing at a near all-time low. This is a stark comparison to 2011, when heavy rains and a large snowmelt in the spring sent record levels of water and sediment flowing down the river. At the Old River Control Structure north of Baton Rouge, the flow of the river is split, with 70 percent continuing down the Mississippi to the Bird’s Foot delta, and the remaining 30 percent flowing down the Atchafalaya River. During the 2011 flood, the flood protection levees and the opening of the Morganza and Bonnet Carré spillways successfully shunted water safely past the high population centers in the region. However, this event was a missed opportunity to capitalize on the influx of fresh water and sediment and to reconnect the river with sediment-starved wetlands of Louisiana.
In a recent study published in Nature Geoscience, research led by Federico Falcini, Ph.D. examined the link between the historic 2011 river flood and sediment accumulation in nearby wetlands. Their analysis suggested that the natural dynamics of the coastal system coupled with man-made alterations to the river system influenced the amount of sediment deposited in the wetlands. This work shows that under river flood conditions, diverting the flow of the river into shallow basins adjacent to the river could contribute significantly to sediment deposition in the wetlands and therefore contribute to wetland growth.
In the study, the sediment plumes of the Mississippi and Atchafalaya Rivers were tracked using satellite imagery from the 2011 flood event to understand where the sediment went once it exited these rivers. The Mississippi’s sediment plume exited the river in focused jets of sediment-laden water due to the confinement of much of the river’s flow between artificial levees. This plume moved past the coastal current and into the deeper waters of the Gulf of Mexico, limiting the amount of sediment that could be deposited in the near-shore area and adjacent wetlands. In contrast, the Atchafalaya’s sediment plume exited the river and moved along a broad, near-shore area, mixing with waters from the Gulf of Mexico and creating conditions that were likely to favor sediment deposition.
A comparison of sediment accumulation during the 2011 flood in nearby marshes shows a trend that corresponds to the difference in behavior of the two river plumes. Sediment accumulation was highest at marsh sites near the Atchafalaya River, which supports the idea that its sediment plume spreading out over a large area in relatively shallow water, promoting increased sedimentation in the region. Sediment accumulation in wetlands near the mouth of the Mississippi River was substantial, but significantly lower than near the Atchafalaya. While the Mississippi River carried a larger sediment load during the 2011 flood event, much of the sediment was lost to the deeper waters of the gulf.
Louisiana’s 2012 Coastal Master Plan identifies several sediment diversions that are key to restoring the important coastal Louisiana landscape. The success of these diversions will depend on a variety of factors, including location and operation. However, this new research confirms that fine sediments introduced into shallow water can substantially contribute to sediment accumulation in wetlands. In order to restore the rapidly deteriorating wetlands of coastal Louisiana, it is critical to reintroduce the sediment that once built this productive region.2 Comments
By John Lopez, Ph.D., Lake Pontchartrain Basin Foundation
The Bohemia Spillway, located along the east bank of the Mississippi River two miles south of Pointe a la Hache, La., is a rare opportunity to observe the natural processes and potential benefits of the Mississippi River flow into the Louisiana wetlands. Because there is no artificial river levee to obstruct flow during high water, the river has been flowing into the adjacent wetlands for 85 years. In 2011, the Lake Pontchartrain Basin Foundation (LPBF) conducted a hydrologic study of how much water enters the spillway and where it flows during floods. It was over the course of this work that LPBF researchers made an unexpected discovery: a new channel was being cut by the flowing water from the Mississippi River.
As the 2011 flood waned, we began noticing this new channel, and in July, the channel made a dramatic breach into the nearby roadway. On Mardi Gras Day 2012 (Feb. 21), scientists noted that the channel had reached the bank of the Mississippi River and shortly after, a complete breach into the river occurred. With this milestone, the channel is now an extension of the Mississippi River that helps distribute the river flow through the new distributary channel.
At this time, the distributary flow through the newly-dubbed “Mardi Gras Pass” is small, estimated to be less than 1% of the river’s peak discharge (5,000 to 10,000 cubic feet per second). The channel is 30 to 40 feet wide near the river but deep enough to capture river flow continuously even under very low water. This new diversion was not manmade – it was the result of natural river forces seeking a shorter outlet to the sea.
It can be expected that Mardi Gras Pass will expand over time. The rate of enlargement is of great interest because this process has not been observed in modern times, and the concern is that the diversion may become too large. However, enlargement of the pass may be desirable, because just one mile away, the new draft Louisiana Coastal Master Plan recommends a large diversion of about 4% of the river’s peak flow (50,000 cubic feet per second). This new diversion is estimated to cost $220 million, so LPBF is encouraging the state and Army Corps of Engineers to consider Mardi Gras Pass as an alternative, since it may provide the same wetland benefits for a much smaller cost and much sooner than a constructed diversion.
Another exciting aspect of Mardi Gras Pass is the rapid emergence of the riverine ecology. When the channel was just a few weeks old, schools of fish were observed migrating up current toward the river. These pogy fish were feasting on the plant detritus being washed into the pass from the river. The influx of fish to the area attracted river otters, which have been commonly observed feeding in the pass. Additionally, beaver, heron and other critters have begun taking advantage of the bounty created by the river flow in Mardi Gras Pass.
Support for this research is provided by The McKnight Foundation, Environmental Defense Fund, The Walton Family Foundation, Surdna and The National Audubon Society. To learn more about LPBF and the Bohemia Spillway, please visit SaveOurLake.org (go to Coastal > Technical Reports > Bohemia Spillway Documentation).
- Video: Bohemia Rising: Exploring the Mississippi Delta in South Louisiana, (Lake Pontchartrain Basin Foundation).
- Resiliency of the Bohemia Spillway and the Evolution of Mardi Gras Pass, Southeast Louisiana, (Lake Pontchartrain Basin Foundation).
By John A. Lopez Ph.D., Lake Pontchartrain Basin Foundation
The Bohemia Spillway area—a 12-mile reach on the east bank of the Mississippi River approximately 45 miles downriver of New Orleans—is a focus of research by the Lake Pontchartrain Basin Foundation (LPBF). The spillway has a fascinating history. In the 1920s, New Orleans residents had great fear of flooding from the Mississippi River, so the state authorized removal of artificial river levees to create a relief outlet for floodwater. In 1926, the artificial river flood protection levees near the Bohemia Plantation were removed, thus creating the Bohemia Spillway. This flood protection project also fortuitously created a wonderful scientific experiment of reintroducing the river floodwater to the adjacent wetlands.
We find today that the wetlands near the spillway are healthier and more resilient than elsewhere in Louisiana. Other than some modest shoreline erosion, the wetlands seem very stable. Other causes of land loss do not seem to be active. Typically elsewhere, oil and gas canals create direct loss of wetlands and an indirect effect by changing the wetland hydrology. Many areas of coastal Louisiana have lingering land loss by canals created decades earlier. Not so in Bohemia. There is no pattern of “indirect loss”. Rather, many canals are filling in with sediment and marsh. Some have been completely reclaimed back to marsh. The response to the oil and gas canals is one of resilience rather than weakness. This resiliency is probably due to the river’s reconnection 85 years earlier.
LPBF has been investigating the spillway since 2007. During the great spring flood of 2011, a major effort was undertaken to research and understand the interaction of the river’s overbank flooding and effect on the wetlands. It is hoped that some of these documented natural processes can be replicated elsewhere in coastal Louisiana to make the coast more resilient.
LPBF will be releasing a major report on the spillway in 2012, as well as releasing a video introducing the Bohemia Spillway and this research.2 Comments
This piece was originally posted on National Wildlife Federation's Wildlife Promise blog.
By Maura Wood, National Wildlife Federation Coastal Louisiana Senior Outreach Coordinator
Our boat left the canal, rounded a small spit of land, and emerged into the outfall area of the Caernarvon freshwater diversion, known as Big Mar – Big Sea. Situated in the last big bend of the Mississippi River about a half an hour drive south of New Orleans, this failed agricultural enterprise of the past shows up on satellite photos as a big square lake. Recent imagery had suggested that perhaps some mud shoals had developed as a result of the diversion.
But today, I wasn’t looking at mud shoals. I was looking at acres of bushy, green, growing, happy vegetation. This couldn’t be Big Mar. This was “Big Mar-sh”!
Caernarvon is the diversion everybody loves to hate. “It doesn’t work,” they say. “It hasn’t built land. What good is it?”
I always sigh when I hear that. Diversions should be a way of reconnecting the water and sediment of the Mississippi River, constrained within levees, with the nearby marshes which, pre-levee, were built and sustained by annual flooding of the river. Caernarvon is not that kind of sediment diversion, it is a freshwater diversion only, designed to lower salinities in an area where saltwater had intruded. Although the water of the Mississippi River contains lots of mud and sand, this diversion project didn’t focus on land-building, and was built instead to provide fresh water to a basin being inundated with salt.
But sitting in the boat, in an area that could no longer be referred to as a sea but rather a sea of plants, we were stunned at what the river had wrought. “This is more than I ever expected,” said John Lopez, a seasoned wetland scientist and executive director of the Lake Pontchartrain Basin Foundation. “This is phenomenal.”
David Muth, the National Wildlife Federation’s Louisiana state director, reached into the shallow water and grabbed a handful from the bottom. “It is mixed sand and silt. Once these plants become established, this marsh will not be washing away in the next hurricane, the way nearby organic soils did in Katrina. This is solid ground.”
So even though the design and intention of this particular diversion hadn’t encouraged it to, the Mississippi River had done what it does – build land. Caernarvon was opened in 1990 and over the years, it’s transported and deposited sand and mud into Big Mar, a little at a time, year after year.
Small areas of land began emerging after Hurricane Katrina. Big flood years on the river in spring 2008 and 2010 provided extra amounts of sediment, and the extended opening of the diversion during the oil spill a year ago might have contributed additional sediment as well, so that when the water receded, more land emerged. And in south Louisiana, it doesn’t take long for plants to take root, grow, and enhance land-building by trapping and holding even more sediment. The spring and summer of 2011 did the trick, and what looked promising a year ago looked spectacular today.
Our boat captains and Chris Macaluso of the Louisiana Wildlife Federation, NWF’s state affiliate, pointed to seed heads on the marshy plants that will feed flocks of ducks in the near future. A few blue-winged teal and mottled ducks served as tantalizing harbingers of the hundreds to follow.
On some of the higher areas, small trees demonstrated the progression of vegetation and habitats that can be expected as land continues to build and emerge from the water. David Muth probed the muddy bottom with a measuring pole to determine water depths–6 inches, 12 inches, 6 inches–in an area originally several feet deep. It won’t be many more years before we can expect those shallow areas to fill and even more land to emerge. Check out comparison photos in this Lake Pontchartrain Basin Foundation report (PDF).
The National Wildlife Federation is committed to restoring a sustainable coast in Louisiana, and the capacity of the Mississippi River to transport sand and build land is a powerful tool. Our trip to Caernarvon provided a first-hand re-affirmation, once again, of this power. At Caernarvon, we didn’t particularly help the river–and it took a long time–but it is doing what the river does – transporting and depositing sand, and building land.
Imagine what a diversion can do that is built to enhance this capacity? We are now capable of marsh-building diversions, that focus on capturing high concentrations of sediment.
So enough about “Caernarvon doesn’t work.” Caernarvon is showing us that the Mississippi River builds land. It always has, and it always will.1 Comment
By David Muth, National Wildlife Federation
On June 22, members of the Mississippi River Delta Restoration Campaign visited the West Bay Sediment Diversion site to make a preliminary assessment of effects of the great Mississippi River flood of 2011. What they found exceeded expectations. Standing where flood water had risen to waist deep level or even deeper, they now stood in ankle deep water on a hard sand bottom. Based on this observation, there is every expectation that when the Mississippi flood waters completely recede, new land will emerge in the delta and marsh plants will begin to colonize it.
The West Bay Sediment Diversion Project, which began as one of the great early hopes of the Coastal Wetland Planning, Protection, and Restoration Authority (CWPPRA) program, recently has become a problem child, derided as a failure, and blamed on dubious evidence for causing shoaling in an anchorage downriver. The concept was simple: to build a bigger version of the many uncontrolled artificial crevasses that have been used quite successfully – 50,000 cubic feet per second, equal to the volume of several Colorado Rivers – on a very small scale, to sustain the sinking Bird’s Foot Delta over the last few decades.
However, when rapid emergence of land failed to materialize as it had on so many smaller projects, diversion skeptics pounced, claiming it proved that large-scale sediment diversions could not work quickly enough to help save coastal Louisiana. For a host of reasons, those criticisms were unjustified. Unfortunately, the navigation issue, which had driven up the cost of the project because it required that additional dredging be covered by CWPPRA, seemed to be the nail in the coffin. As a result, the CWPPRA Task Force has voted to de-authorize and close the diversion, killing the project.
Fortunately, the reports of death were premature. CWPPRA now will be faced with a dilemma: the diversion is working, rebuilding marsh that disappeared over the last 50 years. In addition, it is saving precious sediment from drifting into the deep gulf and being wasted. How can the Coastal Wetland Restoration Authority kill a project that is building marsh?No Comments
By Elizabeth Skree, Environmental Defense Fund
The National Oceanic and Atmospheric Association (NOAA) is predicting an above-average hurricane season, which starts today, so communities along Louisiana’s coast are bracing for yet another possible disaster. The historic Mississippi River floodwaters have barely begun to recede. Additionally, the Gulf is still recovering from last summer’s devastating BP oil disaster. These tragic events, in addition to the ongoing rapid land loss along Louisiana’s coast during the last eight decades, continue making the state’s coastal communities and cities vulnerable to disaster.
Every hour, more than a football field’s worth of Louisiana’s wetlands disappear. These wetlands act as a natural storm surge barrier, protecting Louisiana’s coast. As land loss caused by sinking land increases, these vital wetlands disappear, leaving people and infrastructure exposed and vulnerable. Numerous industries, communities, and wildlife depend on the Mississippi River Delta for survival, and it is imperative that the region be revitalized and restored for the future of the region and the nation.
One way to bring Louisiana’s coast and the Gulf back to health is for Congress to dedicate at least 80 percent of Clean Water Act penalties from the BP oil spill to Gulf restoration. The states that were devastated by last summer’s disaster deserve compensation, especially in Louisiana, where the ecological damage was greatest. This money can be used to replant damaged wetlands, which will in turn help protect the state from future disasters. Directing BP’s fines to Gulf restoration will make the region safer and better than it was before the oil spill. And with the six-month hurricane season starting today, we have no time to lose.1 Comment
By Seyi Fayanju, Environmental Defense Fund
When you hear about the floodwaters coursing through the Mississippi River Valley, it's hard to visualize just how much water is rushing south towards the Gulf of Mexico. Now, courtesy of the U.S. Department of Agriculture's Mississippi River Floods May 2011 Flickr site, the Atlantic Magazine, the U.S. Army Corps of Engineers New Orleans District's Flood Fight 2011 Flickr site, Louisiana State University's Earth Scan Laboratory and NASA's Earth Observatory (to name a few), you can see the power of this spring deluge.
These pictures reveal the wide band that the river has cut through cities and farmland north of the river delta. Notice how brown the river is. Like some bizarre pipeline from a Willy Wonka fantasy, the river streams southward with a color that ranges from caramel to chocolate depending on your perspective. That's because the water is channeling soil and sedimentary material from nearly 30 states (and two Canadian provinces) by the time it hits the Louisiana state line. From there, the Mississippi River is joined by a few more tributaries before it begins to branch out.
The main channel of the Mississippi usually carries most of the river water as a result of an engineering project called the Old River Control Structure. However, because of the heavy volume of water pushing down towards Louisiana, much of the river water has been diverted into spillways. This relieves pressure on levees along the main branch of the river, but it leads to a dramatic increase in water and sediment flows into Lake Pontchartrain, the Atachafalaya River, and other basins near the modern Mississippi River delta.
However, the most compelling visuals of the river's power are the satellite photos from NASA's MODIS satellite, which reveal the extent of the sediment plumes (photo below).
This spring isn't the first time the Mississippi River has topped its banks. In fact, long before it was leveed off, the river routinely deposited sand and fine material near its mouth as it built what we now call coastal Louisiana. If we could fly back in time, we would have seen the swollen river building different delta lobes over several millennia. The interruption of this process is an important reason why the wetlands of southern Louisiana are now disappearing at a rate of an acre each hour.
Each grain of sediment that pours into deep waters of the Gulf from the main stem of the Mississippi is a lost opportunity to save Louisiana. Under ideal conditions, a significant portion of this sediment (some estimates range as high as 30 to 70%) would build the soils of the river delta and portions of the remaining sediment can replenish the delta. For that reason, we hope that these images from above (as well as the stories of everyday people on the ground who deal with land loss) will motivate Washington to get serious about efforts to re-engineer the Mississippi River and rescue its delta.
If a picture is worth a thousand words, we want this compelling gallery of images to send this clear message to Congress: save southern Louisiana before it's too late.1 Comment