Archive for Diversions
This was originally posted on the Coalition to Restore Coastal Louisiana's Coastal Currents blog.
The much-debated West Bay Diversion will remain open for at least the next 10 years. That’s the word from the CWPPRA Task Force, which reversed its own 2008 decision to close the sediment diversion at its meeting on Thursday, October 12, 2012.
The move keeps open one of the few land-building diversions off of the Mississippi River, allowing sediment in nearby wetlands to continue to accumulate. Researchers will also have the opportunity to continue studying the diversion, which has reportedly built more than 10 acres of land in 2011 alone.
Quoted by The Advocate’s Amy Wold on Thursday, Colonel Ed Fleming of the U.S. Army Corps of Engineers said new research suggests the diversion is providing more benefit to the surrounding wetlands than first thought. “It appears the diversion is working better than expected,” he said. “When the task force made the decision a few years ago to close this, we didn’t have all the information we have today.”
The original decision to close West Bay was based on a complicated funding scenario that concluded the diversion was not providing enough benefit to justify the expense of keeping it open.
In light of new evidence, the CWPPRA Task Force decided to allocate the money it would have spent closing the diversion to take the necessary steps to keep it open for 10 more years.
While the West Bay Diversion has been criticized over the years for flaws in its design and the expense of keeping it open, the decision to keep the diversion running is important. The 2012 Coastal Master Plan, passed by the Louisiana Legislature this summer, relies on the use of properly designed and operated sediment diversions to rebuild sections of our delta. The acres of land created by West Bay lend credence to the position that these diversions will work. The opportunity to study a working sediment diversion is valuable to researchers who have few other options for studying this restoration method in the field. If West Bay continues its recent track record of success, it will also help proponents of diversions convince policymakers, and the public, of the worthiness of sediment diversions within Louisiana’s coastal restoration strategy.No Comments
By David Muth, Louisiana State Director, National Wildlife Federation
Now that Louisiana’s 2012 Coastal Master Plan is law, it is critical that the state’s Coastal Protection and Restoration Authority (CPRA) moves the process forward as quickly as possible. While the plan lays out a series of projects for over its fifty-year timeframe, the actual sequence of projects has not yet been completely planned. The sooner CPRA can finalize this project list and timeline, the sooner vital construction and restoration can begin.
Several things are necessary for creating that list of projects. First is to carry out continued modeling to measure how projects and suites of projects will interact with one another. One example is looking at how a mid-Barataria 50,000 cubic feet per second (cfs) sediment diversion will interact with marsh creation projects in the middle Barataria Basin and with a ring levee and community resiliency measures for the nearby town of Lafitte.
Second is to work out how funding streams can be most effectively sequenced to begin building out the projects identified in the list. This is especially critical with Clean Water Act penalty funding to be distributed under the RESTORE Act and the separate Natural Resource Damage Assessment (NRDA) process. These funding sources, resulting from the BP Deepwater Horizon oil spill, could become available at almost any time over the next few years.
Third is to move quickly to implement nonstructural hurricane risk reduction measures. Nonstructural storm protection measures are those that build community resiliency by means other than “structural” methods such as levees, floodwalls and floodgates. They include raising structures and homes up out of danger, hardening infrastructure and assisting with voluntary relocation. Unfortunately, the suite of existing nonstructural programs is reactive: invoked after, but not before, a disaster. That has to be changed moving forward.
Another challenge concerns the Chenier Plain in southwest Louisiana. The key to long-term restoration in that area is to find ways to modify the hydrology of the area’s navigation system to prevent the continued influx of sea water into formerly freshwater marshes. Simple on paper, tricky in practice.
At an implementation level, two important capabilities need to be developed for the master plan to move forward. One is to demonstrate the feasibility of long-distance pipeline sediment delivery. Much of the Coastal Master Plan depends upon finding a viable way to move vast volumes of sediment many tens of miles through dredge pipes. We have a great deal of experience with relatively smaller scale projects for both marsh creation and barrier island restoration, but the master plan proposes projects that will be carried out on a much larger scale — moving material over much greater distances than ever before. While there seems to be no technical reason this cannot be done, actually doing it will be important for fine tuning the plan.
Similarly, we need to test and demonstrate a sediment diversion somewhere other than at the mouth of the Mississippi River. The very existence of southeast Louisiana proves that such diversions build land. We have extensive experience cutting artificial distributaries near the mouth of the river and letting them build land – from Cubit’s Gap and a dozen other cuts on the Mississippi below Venice to the Wax Lake Outlet on the lower Atchafalaya River. We also know that crevasses through the man-made levee system prior to 1928 moved vast quantities of sediment into the upper estuaries. But we have never deliberately designed and constructed a controlled sediment diversion, and we will learn a great deal more than modeling can tell us by actually doing it.
All told, the to-do list for Coastal Master Plan implementation seems long, but with RESTORE Act and NRDA fines on the way, we will have the funding to jumpstart restoration. Combine this funding with the proper planning and prioritization, and coastal Louisiana will take several steps closer to a more sustainable future.1 Comment
At just five months old, Mardi Gras Pass is the newest distributary of the Mississippi River – a modern addition to an ancient system. Located about 50 miles south of New Orleans on the east bank of the river, the pass was discovered by Lake Pontchartrain Basin Foundation (LPBF) staff on Mardi Gras Day 2012. The natural flow of the Mississippi River had cut a continuous channel through the river’s bank and into the Bohemia Spillway, creating a new distributary and offering a small glimpse at what a natural delta system looks like.
On August 1, Louisiana’s Governor’s Coastal Advisory Commission held their regular meeting in Davant in Plaquemines Parish. At the meeting, Dr. John Lopez, executive director and coastal sustainability program director for LPBF, presented on the status of Mardi Gras Pass to the commission. The presentation showcased how LPBF and its partners were taking every advantage to study and learn about the river’s natural ability to connect to the wetlands. In June, LPBF released a report on the dimensions of the new channel, and its staff continues to regularly monitor the pass’s progress. Both the report and Dr. Lopez’s presentation can be found at SaveOurLake.org.
Mardi Gras Pass’s flow has increased modestly since February, but the discharge is almost entirely dependent on the height of the Mississippi River water level. This summer, while the river has been exceptionally low, the flow rate has been less than 500 cubic feet per second. But when the river rises toward the end of the year, the flow could be ten times greater.
The Governor’s Commission also visited Bohemia Spillway and Mardi Gras Pass themselves. They were taken to a location where the newly-established Mardi Gras Pass has cut through a private road within the spillway, making it impassable. A local oil company has applied for a permit to repair the road, which could close off the flow from the river and block the pass. The state has expressed scientific interest in Mardi Gras Pass and recognizes it as a potential restoration opportunity. Therefore, the state has requested that the company evaluate alternatives to repairing the road which would allow the pass to still function.
The Commission also visited the actual location where Mardi Gras Pass has cut through the Mississippi River’s bank. Some Commission members had never seen the Mississippi River without an artificial river levee, and it was a moving experience to see the river in its natural condition and to see the meandering Mardi Gras Pass’s channel cutting through the river’s willow tree forested bank. Mardi Gras Pass is a real-life example of nature at work. As a natural distributary and natural diversion, Mardi Gras Pass represents a small precursor to what a more natural Mississippi River and delta could look like in a Coastal Master Plan future.
- Presentation to Governor's Commission: Status of Mardi Gras Pass, the Newest Distributary Pass of the Mississippi River within the Bohemia Spillway, Southeast Louisiana (Lake Pontchartrain Basin Foundation)
By Whit Remer, Policy Analyst, Environmental Defense Fund
It’s been an exciting year for Louisiana and the Mississippi River Delta Restoration Campaign.
In July 2011, nine gulf senators banded together and introduced the RESTORE Act – legislation that would ensure penalties paid by BP and others responsible for the gulf oil spill would be used to restore the gulf region’s environment and economy. In September, the Senate Environment and Public Works Committee approved the bill and in October, Representative Steve Scalise (R-LA) and 20 other gulf representatives introduced the House version of the bill. Supporters worked hard and waited patiently as the RESTORE Act continued winding its way through congressional hearings and historic votes until finally, on June 29, 2012, the RESTORE Act was included as part of the final transportation bill and days later signed into law by the President. It was an amazing journey from start to finish, and we want to take a moment to reflect on the past year and begin looking forward to how the RESTORE Act will unfold to become the single largest environmental restoration investment ever made by Congress.
The idea of spending penalty money from the oil spill on environmental and economic restoration in the gulf region is only fair. Diverse groups, including conservation organizations, the Secretary of the Navy, chambers of commerce from across the gulf region and even a special commission created by the President in response to the spill, all agreed it was the right thing to do. Heeding this call, Congress came together to design a bill to return the money where it belongs: to the Gulf Coast. In the Senate, the RESTORE Act received 76 votes – a remarkable display of bipartisanship which highlights the broad support had by the bill. Of course, it could not have happened without our campaign’s supporters, who used social media, letters to the editor and appeals to their congressional representatives to make the bill a top priority.
Looking forward, we are excited that the RESTORE Act has the potential to make the environment and economies of the Gulf Coast healthy again. The RESTORE Act includes a list of various eligible activities that states may use funds for, ranging from coastal restoration and shoreline protection to seafood and tourism promotion. All of these activities will provide new job opportunities for residents along the Gulf Coast and across the nation. As a recent Duke University report shows, the RESTORE Act is a win for the entire country.
The RESTORE Act also sets up a Restoration Council comprised of various federal agencies and states affected by the spill to create an environmental restoration plan for the Mississippi River Delta and Gulf Coast. The plan has the potential to address major, and very expensive, challenges in the Mississippi River Delta. A top funding priority in the plan for Louisiana will be designing and constructing large-scale sediment diversions along the lower Mississippi River. Sediment diversions provide wetlands with essential supplies of fresh water and new silt which help rebuild land and protect the coast.
Over the next few months, the Mississippi River Delta Restoration Campaign will update readers on important RESTORE Act developments. We hope to provide you with useful information as the Restoration Council forms and begins the important process of creating a restoration plan for America’s Gulf Coast.
Stay tuned.1 Comment
The Next 50 Years: Climate change and the Coastal Master Plan: “Hope for the best but plan for the worst”July 19, 2012 | Posted by Delta Dispatches in 2012 Coastal Master Plan, Coastal Master Plan series, Diversions, Hurricanes, Science
By Dr. Doug Meffert, Executive Director, Audubon Louisiana
Louisiana’s 2012 Coastal Master Plan takes a realistic and critical examination of the effects of climate change impacts on the future of coastal Louisiana, both in terms of prioritization of restoration projects as well as risk reduction. In its “less optimistic scenario,” the master plan estimates 0.45 meters of sea level rise over the next fifty years. This is in addition to between zero and 25 millimeters per year of land subsidence, with the fragile deltaic plain having the highest rates. The resultant combination of sea level rise and subsidence predicts that relative sea level rise will be more than one meter during the next century in some areas of the Mississippi River Delta. Additionally, this scenario anticipates a 20 percent increase in storm intensity and a 2.5 percent increase in storm frequency for Category 1 hurricanes and greater. As climate change brings more severe storms and rising seas to Louisiana’s coast, it is important to incorporate these predictions into the formulation of the Coastal Master Plan.
This “less optimistic scenario” predicts a very different and more vulnerable coast than we had in the 20th century. The master plan uses this scenario for its predictions for future flooding from a 100-year event and for prioritization of restoration projects, since what is labeled as “less optimistic” in the report could just as accurately be labeled as “increasingly likely.” This scenario is consistent with the recent assessments by the Intergovernmental Panel for Climate Change (IPCC), the findings from the Durban Climate Change Conference in November 2011, and more recently, peer-reviewed articles (Blum and Roberts, 2012; Day et al., 2012). In fact, one of the master plan’s Science and Engineering Board members, Dr. Virginia Burkett, was a coauthor of the IPCC’s 2007 report, which garnered the 2007 Nobel Peace Prize for the IPCC.
“Hope for the best but plan for the worst” is the adage adopted by the Coastal Master Plan, and I couldn’t agree more. As it is, there is not enough sediment in the Mississippi River to offset the predicted land loss from relative sea level rise and erosion if we do nothing. This means we need to act now for a future coast that supports the fisheries, birds and other ecological services upon which we depend. We need to plan for a future coast that still provides a natural storm surge buffer for our cities, towns and critical infrastructure. That future coast will just be different than what we’ve known in the past. And that future coast depends on implementing large-scale river diversions with no further delay. We finally have a realistic master plan based on the best science possible. Now, we just need to implement it.
This is the fourth post in our "The Next 50 Years" Coastal Master Plan series. Check back as we continue diving into the master plan and what it means for the people and environment of the Mississippi River Delta.
By Alisha A. Renfro, Ph.D., Staff Scientist, National Wildlife Federation
To formulate Louisiana’s 2012 Coastal Master Plan, coastal authorities evaluated nearly 250 restoration projects that had been proposed in previous parish- and state-level restoration plans. This number was then narrowed down by setting a realistically achievable budget, modeling for future environmental conditions and understanding how the implementation of individual projects could help sustain or build land over the next 50 years. Projects included in the Louisiana Coastal Area (LCA) Comprehensive Study were among those considered for inclusion in the master plan, and many of these projects – or similar versions of them – were included in the 2012 Coastal Master Plan. By incorporating these projects in the long-term vision of restoration for coastal Louisiana, these projects will be better integrated with others in the master plan. Additionally, inclusion of these LCA projects shows the state’s commitment to their construction and implementation.
The LCA Program was authorized through the 2007 Water Resources Development Act and includes 15 near-term critical restoration projects. As part of the LCA Program, the state of Louisiana and the U.S. Army Corps of Engineers work together to plan and implement these 15 projects. To date, construction has not begun on any of these projects, and as they near the construction phase, the lack of federal funding in the immediate future threatens to delays them indefinitely. That is, until Congress passed the RESTORE Act in June. Signed into law just last week, the RESTORE Act will ensure that 80 percent of the Clean Water Act fines BP and other responsible parties will pay as a result of the 2010 gulf oil spill are dedicated to environmental restoration in the gulf states. In Louisiana, this money will be used to help fund the restoration projects outlined in the master plan.
Of the 15 LCA projects, nine were included in the 2012 Coastal Master Plan. But in many cases, the project selected and described in the master plan is a modified version of the original LCA project. This is a result of the analysis conducted in the planning process that indicated that modifications to the project would increase the land it built or maintained. However, it should be noted that the projects described in the master plan are still conceptual, as their exact size and location will be determined through further planning and design. Below is a list of the LCA projects and a brief description of the corresponding project included in the master plan.
The extensive analysis that went into formulating the master plan indicates that the capacity of several of the LCA sediment diversions may need to be scaled up in order to maximize the amount of land they can build and sustain. By including so many LCA projects in the plan, coastal authorities reaffirmed the importance of these critical projects to restoring the coastal Louisiana landscape. Moving away from smaller restoration projects toward larger ecosystem-scale projects will help restore the natural hydrology and mimic the processes that built the Mississippi River Delta, thus creating a more sustainable coastline for the people who call the region home.No Comments
This is the second post in our "The Next 50 Years" Coastal Master Plan series. Check back as we continue diving into the master plan and what it means for the people and environment of the Mississippi River Delta.
By Alisha A. Renfro, Ph.D., Staff Scientist, National Wildlife Federation
Since 1932, coastal Louisiana has lost almost 1,900 square miles of land and if bold action is not taken, another 1,700 square miles could be lost by 2060. Louisiana’s 2012 Coastal Master Plan, passed last month by the state legislature, is a 50-year strategy that aims to realistically, but aggressively, use numerous restoration tools to ensure a sustainable and more resilient coast. The plan’s analysis indicates that sediment diversions, structures that allow Mississippi and Atchafalaya River water to be moved strategically into the surrounding wetlands, are critical projects for halting land loss and building a more sustainable coastline for the future of the Mississippi River Delta.
Ten projects identified as sediment diversions were judged as important restoration tools in the plan. Sediment diversions mimic some of the natural processes that once built the Mississippi River deltaic region. By operating these types of control structures when river discharge is high, the large amount of sediment, that is being moved along with the water, is captured and funneled into the nearby wetlands. The introduction of sediment would not only help restore areas that are today shallow open water, but it would also help prevent future wetland loss due to rising sea levels.
Sediment diversions can build new marsh by transporting sediment-laden water from the river into the nearby basin. The heavier sand sediment is deposited quickly and over time, and a marsh platform is built. Once vegetation begins to colonize the area, sediment deposition increases as silts and clays are trapped by plants, and a new marsh will emerge. Sediment diversions can also help sustain the newly-built and existing marsh as sea levels rise, by providing a source of sediment that can be deposited on the marsh surface. Ultimately, this can increase the elevation of the marsh surface, which helps prevent prolonged flooding of the marsh, even as sea levels rise. Sediment diversion critics have voiced concerns about the introduction of fresh water into these basins and have questioned whether diversions are essential to restoring Louisiana’s coast.
To evaluate the necessity of the sediment diversion projects in the master plan, the authors conducted an experiment to analyze the amount of land that could be built only using other types of restoration tools. The results of this experiment indicated that by removing the sediment diversion projects from the plan, total land built would be reduced by 340 to 630 square miles over the 50 years. This indicates that sediment diversion projects are crucial projects in the plan and necessary for rebuilding the Mississippi River Delta.
A similar experiment was conducted to address questions about using a few larger sediment diversions versus multiple smaller diversions. The multiple small diversions not only affected the benefits that people get from the land, such as oysters, as much or more than larger diversions, but the smaller diversions also built significantly less land over the next 50 years.
The restoration projects selected in the 2012 Coastal Master Plan may potentially build or sustain up to 800 square miles of land over the next 50 years – land that otherwise would be lost. While sediment diversions are not the only types of restoration project identified as critical to the future of the Louisiana coastline, scientific assessment suggests they are absolutely necessary. Other types of projects, such as barrier island restoration and marsh creation, can build land quickly, but without tapping into the sustainable power, sediment and fresh water of the river, these projects cannot be maintained over the long term.
The land loss crisis in Louisiana requires aggressive action. Louisiana’s 2012 Coastal Master Plan shows us that the path forward for building a more sustainable and resilient coastline is by reconnecting the Mississippi River to the landscape it once built.No Comments
By Whit Remer, Policy Analyst, Environmental Defense Fund
In late April, the Deepwater Horizon Natural Resource Damage Assessment (NRDA) Trustees finalized the first phase of projects to address Gulf Coast environmental damage caused by the 2010 oil disaster. The trustees are a group of federal and state representatives charged with overseeing environmental restoration following the oil spill. The project document, known as the Deepwater Horizon Oil Spill Phase I Early Restoration Plan and Environmental Assessment (ERP/EA), comes on the heels of the draft version released in February for public comment.
The document includes a variety of projects across the gulf, including oyster restoration, wetland creation and improvements to public amenities. Rightfully, the trustees have considered a diverse suite of restoration options, and we encourage them to continue exploring the use of sediment diversions to achieve restoration goals in the Mississippi River Delta.
One of the most promising techniques for restoring, rebuilding and stabilizing wetlands in coastal Louisiana is the use of sediment diversions along the Mississippi River. Diversions replenish wetlands adjacent to the river with the fresh water, nutrients and sediments necessary to maintain healthy ecosystem functions. The State of Louisiana recently recognized the importance of such diversions in the 2012 Coastal Master Plan, which the State Legislature unanimously passed earlier this month. The master plan outlines a 50-year, $50 billion strategy to restore Louisiana’s coast and protect communities. Diversions are a critical component to achieving the long-term and comprehensive restoration envisioned by the plan.
The final Phase I ERP/EA includes the Lake Hermitage Marsh Creation project, a small-scale sediment pipeline project in Plaquemines Parish. The project will transport fresh water and sediment from the Mississippi River through a pipeline to wetlands adjacent to the river, and is expected to create over 100 new acres of marshland at a cost of $14 million. Pipeline projects have been effective in Louisiana in the past, but they do not provide the long-term sediment flow necessary to sustain the land-building functions needed to restore the coast.
The Lake Hermitage project serves as a good starting point for restoration in the Mississippi River Delta, but to achieve long-term restoration, wetlands need a constant source of sediment and nutrients that pipeline projects do not provide. Moving forward, we recommend NRDA Trustees consider actions that will promote the lasting sustainability of Louisiana’s coast. Without such actions, we may lose a unique opportunity to undertake comprehensive restoration.No Comments
By Meg Sutton, Environmental Defense Fund
Global climate change has induced an increase in global mean sea level with a 3.1 mm/year average rate of increase since 1991. Climate projections indicate a widespread increase of more intense precipitation events, with an associated increased risk of flooding. Similarly, climate scientists also predict an increase in hurricane wind speed and total volume.
The low lying, coastal Mississippi River Delta region is particularly vulnerable to the climate change threats of sea level rise, increased flood risk and more intense hurricanes. The area is additionally plagued by human-induced environmental degradation that has occurred over the past 200-300 years. The region has lost 1,900 square miles of land since the 1930s and is losing the wetland areas that are crucial to the region’s ecosystem function, economy and character.
The numerous threats to the region set up a potential dilemma of competing interests. Should resources and attention be focused on immediate restoration or longer term climate change adaptation? Fortunately, no such choice has to be made. Climate change adaptation and coastal restoration do not constitute a zero sum game. Restoration of coastal Louisiana reduces the vulnerability to the major risks posed by climate change and therefore can be seen as a climate change adaptation strategy.
The global rise in mean sea level — termed eustatic sea level rise — is further complicated in the Mississippi River Delta region by subsidence (sinking land). The sum of the two is referred to as relative sea level rise. The Gulf of Mexico has one of the highest rates of subsidence in the nation due to sediment compaction and the extraction of groundwater, oil and natural gas. These encroaching sea levels increase mean water levels in boundary regions, accelerate coastal erosion and alter the salinity levels of sensitive coastal habitat systems. These factors have contributed to the high rate of land loss in the region.
Restoration of the deltaic system can help stabilize shorelines and reduce the associated risks with rising sea levels. Deltas are formed by the constant inflow of sediment from rivers. However, the Mississippi River Delta has been cut off from this natural process through the construction of extensive levee systems for navigation and flood protection. Through planned sediment diversions, the natural deltaic process can be restored and help increase the resiliency of coastal areas. This will combat the effects of both eustatic sea level rise and subsidence.
The projected increase in the intensity of precipitation events due to global climate change will exacerbate flood risk in the Mississippi River Delta region. Research has shown that coastal wetlands can greatly reduce flooding and storm damage. A one-acre area of wetland can store up to one million gallons of water, providing a significant buffer between flood waters and populated areas. In addition, wetland vegetation acts as a natural flood barrier by reducing the speed of flood waters. Healthy wetlands therefore have the potential to reduce both the volume and speed of floodwaters that reach surrounding areas. Restoration efforts seek to improve the condition of surviving wetlands in the Mississippi River Delta region as well as strategically reestablish historical wetland areas with sediment diversions. The restoration efforts to augment total healthy wetland area in the region will simultaneously reduce flooding risk associated with climate change.
As highlighted by Hurricanes Katrina and Rita in 2005, the coastal Mississippi River Delta region is highly vulnerable to hurricanes and their associated storm surge. Climate change is predicted to increase hurricane wind speed and total precipitation, further amplifying this threat. Coastal wetlands have been shown to reduce both wave energy and wave height when storm surge passes through them. These wetland regions introduce a frictional drag that reduces the intensity of waves, and restoration will therefore help protect surrounding regions from storm surge now and into the future.
The restoration of ecosystem function in the Mississippi River Delta would provide significant benefits for both the short and long-term future of this crucial economic and ecologic zone. The overlapping interests of restoration and long-term climate change adaptation serve to strengthen the case for large-scale immediate restoration of the region.
 IPCC, 2007: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
 Needelman, B.A., S. Crooks, C.A. Shumway, J.G. Titus, R.Takacs, and J.E. Hawkes. 2012 Restore-Adapt-Mitigate: Responding to Climate Change Through Coastal Habitat Restoration. B.A. Needelman, J. Benoit, S. Bosak, and C. Lyons (eds.). Restore America’s Estuaries, Washington D.C., pp. 1-63. Published by: Restore America’s Estuaries 2012
 Wetlands Protecting Life and Property from Flooding. United States Environmental Protection Agency, May 2006.
 Shepard CC, Crain CM, Beck MW (2011). The Protective Role of Coastal Marshes: A Systematic Review and Meta-analysis. PLoS ONE 6(11): e27374. doi:10.1371/journal.pone.0027374
Getting back to nature: New study looks at the past, present and future of the Mississippi River DeltaJune 4, 2012 | Posted by Delta Dispatches in Diversions, Reports, Restoration Projects, Science
By Alisha A. Renfro, Ph.D, Coastal Scientist, National Wildlife Federation
The Mississippi River has played an important role in the history, physical and economic growth of the United States. However, the Mississippi River and the delta region it built didn’t always look the way they do today. In an article by Michael Blum, Ph.D. and Harry Roberts, Ph.D. titled “The Mississippi Delta Region: Past, Present, and Future” published in The Annual Review of Earth and Planetary Sciences (vol. 40), researchers assemble the extensive scientific information that has been reported about the development of the Mississippi River Delta region, the state of the area today and what this means for the future of coastal Louisiana. This study will help scientists plan a sustainable future for the delta.
The modern landscape of the Mississippi River Delta region began to form around 7,000-8,000 years ago. As the river meandered back and forth across the delta plain, it deposited sediments that had been collected from throughout the river’s 31-state drainage basin. Five delta headlands were built as the river changed its course every 1,000-1,500 years across what is now coastal Louisiana. Once the river changes locations and is no longer actively building and maintaining a particular delta lobe, natural processes begin reworking the area, causing marsh to retreat landward and the sandy seaward extent of the lobe becomes a barrier-island arc. It was these processes that formed the Louisiana bayous and barrier islands that we know of today.
The modern day Bird’s Foot delta, also known as the Plaquemines/Balize delta, began forming just over 1,000 years ago. About 500 years ago, the Atchafalaya River, which branches off of the Mississippi River south of the Old River Control Structure, formed the Atchafalaya and Wax Lake deltas, which emerged in the 1970s. Today, active delta building is limited in the Mississippi River Delta to only the mouth of the Atchafalaya River and Wax Lake Outlet as well as a few controlled and uncontrolled diversions an along the Mississippi River. Without more land building opportunities, the delta will collapse.
Modifications along the river system, such as levees and dams, along with sea level rise and higher rates of land sinking have drastically changed conditions along the Mississippi River system that once built and maintained the delta region. Today, rather than migrating back and forth across the deltaic plain, the river is locked in place by an extensive levee system. Even if the river could still migrate, dams and reservoirs in the upper drainage basin states have reduced the amount of sediment carried by the river by half since the 1950s. In addition, sea level rise coupled with land sinking due to compaction of muddy river sediment and fluid withdrawal associated with the gas and oil industry has accelerated land loss in the abandoned delta headlands.
The changes in the river, sea level and sediment supply mean that the future delta landscape will not resemble that of the past. Restoring the delta-building processes of the river will require us to rethink how we manage the resources of the Mississippi River and re-imagine what the future coastline could look like. River diversions that reconnect the sediment and water resources in the Mississippi River to the marsh landscape that surrounds it is a crucial step toward restoring the delta-building and land-sustaining processes of the region.2 Comments