Our Coastal Crisis
Restoration Solutions
Give Now Donate
Wasted Sediment
How the Delta Formed
Anatomy of a Delta
BP Oil Disaster
Restoration FAQs
Priority Restoration Projects
Sediment Diversions
Protect The Funding
What's at Stake
#OurCoast
Explaining the Dead Zone
The Mississippi River's Influence on the Gulf
The Mississippi River is Our Greatest Force for Building Land
10 Fundamental Q & As About the Delta
Fresh Water, Nutrients and Restoring the Mississippi River Delta
Committed to the Long-term Health of Our Coast and All Wildlife
Sediment Diversion Operations
Delta Dispatches Podcast
facebookinstagramtwitterrss
Delta Dispatches
Delta Dispatches: A National Estuarine Research Reserve for Louisiana's Coast
CWPPRA Provides Lessons for Applying Adaptive Management Across Louisiana's Coast
Enjoy the Holidays and Benefit the Environment With These Handy Household Tips
Delta Dispatches Radio Show
Funding & Policy
Hurricanes & Oil Spills
OurCoast
Restoration Project Highlights
We'll deliver a daily digest of our blog posts to your inbox or RSS Feed
Reconnecting the Delta: How Increased Mud Supply Can Improve Sediment Diversions
08.22.2016 | In Science, Sediment Diversions, Uncategorized
Jordan Davis, Mississippi River Delta Restoration Science Intern, Environmental Defense Fund
Rising sea level and anthropogenic sediment loss is a combination affecting sustainability of deltaic ecosystems. Around the world, major deltas have been experiencing a 44% decline in sediment supply since the 1950s due to construction of dams and reservoirs, including the Mississippi River Delta. A recent journal article, published in Estuarine, Coastal and Shelf Science, examined the role of fine-grained sediments in deltaic restoration. The authors found that the supply of suspended mud (silt and clay) to the coast has dropped from a mean of 390 Mt y-1 (megatonnes per year) to just 100 Mt y-1 since 1970. These fine-grained sediments play a crucial role in estuarine ecosystems by sustaining existing marshes.
Almost 100 dams, built as part of the Pick-Sloan water development project, trap mud that once flowed from the Missouri River Basin, resulting in high erosion of very fine sediment, known as loess, in both the eastern and western bank tributaries. Five large reservoirs eliminated sediment from 53% of the watershed. This loss of sediment, with the loss of deltaic wetlands, has hit Louisiana especially hard, and this continued decline in fine-grained sediment flux from the Mississippi River is more important than ever.
(1) (A) Suspended sediment sampling stations in the Mississippi River watershed, modified from Meade and Moody (2010). (B) USGS sediment sampling stations (red triangles) and large dams along the Missouri River Basin, modified from Alexander et al. (2013). (C) Mississippi River Delta Plain and proposed sites of large diversions (Coastal Protection and Restoration Authority, 2012). Image from Kemp et al. 2016.
The wetlands of the Mississippi River Delta are rapidly shrinking. Since 1923, almost 1,250,000 acres have been lost to open water. Initiatives to stop this loss are underway; the Coastal Master Plan calls for at minimum two large (75,000 cubic feet per second) controlled sediment diversions, engineered to encourage land building by reconnecting the lower Mississippi River to its delta.
(2) Annual total suspended sediment and suspended sand loads in the Mississippi River at Tarbert Landing showing relationship between 1950-1969 and 1970-2013, modified from Meade and Moody (2010). Image modified from Kemp et al. 2016
The Mississippi River is naturally effective at building land. Over the last 7,000 nearly 25,000 square miles of new land were built in the delta. Sediment diversions mimic the natural processes that originally built coastal Louisiana by reconnecting the river to its wetlands. Sand transport via sediment diversions allows wetland building in shallow, sheltered coastal bays. However, the finer grained mud that is necessary to sustaining existing marshes will still need to play a role in restoration.
According to the authors of the study, 66% of the missing mud lies in reservoirs on the lowest Missouri River tributaries. Increased mud supply to the delta is possible. The authors found that bypassing 100 Mt y-1 of mud around the dams would increase Mississippi River delta sediment supply within 1-2 decades, and such measures are compatible with the objectives of the Missouri River Restoration and Platte River Recovery Program. Additionally, the authors believe that more mud would enhance river diversions, making them more effective.
Undoubtedly, extensive regional coordination and funding is needed to move fine-grained sediments past as many as 50 Lower Missouri River tributary dams. However, the deterioration of the Mississippi River Delta is so rapid that to just sustain a fraction of the landmass, engineered river diversions and an increase in mud supply are necessary.
Jordan Davis is a summer intern at the Environmental Defense Fund working with the Mississippi River Delta Restoration team. Jordan is a junior at the College of Charleston majoring in geology and minoring in environmental science. Jordan is interested in coastal geology and is excited to apply what she has learned at the Environmental Defense Fund to problems in Charleston; this fall, she will be working on local beach restoration initiatives in the area.
Coastal Louisiana needs your help now more than ever. Sign up to learn more about how you can get involved and help protect America's wetlands for the future. We'll be in touch when opportunities to take action arise, when there are relevant events or volunteer opportunities in your area or when we have important news to share.
Follow us on Instagram at @restoredelta
© 2017–2021 Restore the Mississippi River Delta Privacy Policy Sitemap Site handcrafted by Deep Fried.