How Will a Sediment Diversion Affect the Coastal Environment? The Answer Lies in the Operations.

By Natalie Peyronnin, Director of Science Policy, Mississippi River Delta Restoration, Environmental Defense Fund

Sediment diversions have long been proposed as an essential component in every major restoration plan in coastal Louisiana. Sediment diversions are man-made structures built directly into the Mississippi River levee system with gates that can be opened and closed to allow sediment, fresh water and nutrients to nourish and revive the dying wetlands.

In the “Answering 10 Fundamental Questions about the Mississippi River Delta” report, scientists clearly demonstrated that sediment diversions are the most effective tool to build and sustain land into the future. What have we learned since then? Beyond how a sediment diversion is constructed, its impact and effectiveness lie in how you operate it once built.

Sediment Diversion Design - Restore the Mississippi River Delta

Rendering of what a future sediment diversion may look like. Credit: CPRA.

The Mississippi River built our coastal landscape, and it is the only thing that can truly sustain our coast for future generations. But when and how we utilize the sediment, fresh water and nutrients in the river will determine the effects on the coastal environment, including water quality, salinity, vegetation, and fish and wildlife species.

A recent USGS study concluded that large-scale river diversions, a cornerstone of the Coastal Master Plan, can greatly affect water quality, including salinity, turbidity and nutrients, throughout the estuary, resulting in “dramatic impacts on oyster production.” The authors utilized operation strategies for their study that were based on the 2012 Coastal Master Plan analysis. However, since 2012, we have learned a great deal on how operation strategies used in planning and modeling, such as in the referenced study, can be completely unrealistic for real world operations. Therefore, the predicted outcomes are unrealistic and, more often than not, overestimate the detrimental impacts to the coastal environment.   

To address this concern, the Sediment Diversion Operations Working Group was formed to help define more realistic operation strategies. The group, comprised of 12 Louisiana-based researchers with decades of experience working in coastal Louisiana, came together to discuss how to maximize land-building through a sediment diversion while considering a wide variety of factors including water movement, water quality, vegetation, oysters and shellfish, finfish, wildlife species, natural resource economics, and the communities that live, work and play on the coast. An additional 42 experts participated in the 8 month long process.

The group’s goal was to develop recommendations on how to operate a diversion in the “real world” that maintains a primary objective of building and sustaining land while balancing the needs of the ecosystem and coastal communities. Some of the key recommendations from the report include:

Pulsed operation strategy focusing on winter peaks and rising limb of spring peaks. Note: Although the diversion is depicted as open 100% or completely closed, each opening could happen gradually over time.

For more information on the Sediment Diversion Operations Working Group, visit MississippiRiverDelta.org/DiversionOpsReport

Core members of Sediment Diversion Operations Working Group

Core Members

Title

Expertise

Affiliation

Dr. Rex Caffey

Professor and Director, Center for Natural Resource Economics & Policy

Natural Resource Economics

Louisiana State University

Dr. James Cowan Jr.

Professor

Fisheries

Louisiana State University

Dr. Dubravko Justic

Professor

Oceanography

Louisiana State University

Dr. Alex Kolker

Associate Professor

Sedimentology

LUMCON/Tulane University

Dr. Shirley Laska

Professor

Social Sciences

University of New Orleans

Dr. Alex McCorquodale

Professor

Hydrodynamics

University of New Orleans

Dr. Earl Melancon Jr.

Professor Emeritus/Sea Grant Scholar

Oysters/Coastal Shellfish

Nichols State University/ Louisiana State University

Dr. John Andrew Nyman

Professor

Wildlife and Fisheries

Louisiana State University

Dr. Robert Twilley

Executive Director, Louisiana Sea Grant College Program

Estuarine Ecology

Louisiana State University

Dr. Jenneke M. Visser

Associate Professor and Associate Director, Institute for Coastal and Water Research

Vegetation

University of Louisiana at Lafayette

Dr. John White

Professor

Biogeochemistry

Louisiana State University

James Wilkins, J.D.

Professor, Louisiana Sea Grant College Program and Director, Sea Grant Law & Policy Program

Law/Policy

Louisiana State University

This is part 4 of our ongoing series  where our experts will answer 10 fundamental questions with new and updated information, so that reasonable and scientifically-sound decisions can be made about the long-term sustainability of the delta and surrounding ecosystems. View an introduction to this series as well as posts on sediment, and vegetation.